Model 99 optional twin carbs

I have checked the Norton 1962 parts list at some length, and all the twin carb options are very specifically only for the 650SS and the 1962 88SS.

The earlier Nomad had a twin carb option with tubular stubs (see pic) and there were (and still are) twin carb adapters available for non-draught heads in the form of single alloy billets.

It has been said that all SS Dominators came with twin carbs, and I am virtually certain that is not correct in respect of the 99SS and 191 88SS. In fact I cannot find any documentary evidence suggesting that it was ever a catalogue option for the 99SS at all. If you have anything I would be very interested to see it. There is a 99SS with a single carb on eBay right now with good close ups.

Best Regards

Steve

Well Mr. Marshall, it is maybe time for you to go back to school for reading. On page 57 of Norton publication PS 214, the parts book for 1961 and 1962 singles and twins, it lists a quantity of 2(two) for carburetter part# 376/220 for the 99ss motorcycles. Also on page 55 it lists the same manifold 23739, for both the 1961 88ss and 1961/62 99SS.

Anyone that has researched the subject at all will know that all SS Dominators came with twin carburettors. They would be 376 Monoblocs stamped 376/220.

But the thread start asked about the optional twin carburetters that could be ordered for the standard model 99, the parts for are listed on page 65 of the same publication, part# 18542 for the twin inlet manifold, a quantity of two 376/67 carbs, and other numbers for the needed studs, nuts, cables and fuel lines....

Andrew

The specification is:

376/220 Norton 596cc 1959-60;99 Twin, Mod 99 Sports 1 1/16" Pilot 25 Cutaway 3 Main jet 250 Needle jet 0.106 Needle position 3

The spec is the same for single or twin carb configurations.

HTH

Cheers

Alan

The carb that Alan listed, the 376/220, is for the 1961-62' 650ss model. The other carb, 376/67 is what was listed on the NON-SS model 99 that came from the works with the twin carb option or as parts over the counter for a dealer or owner to install.

Because the 99SS had higher compression than some of the standard Model 99s, and a more sporting camshaft fitted, it might need a carb outfitted with different jets etc..

My data is taken out of an actual parts book for the 1961 and 1962 Model 99 bikes. If your Model 99 is an earlier model than this, then the specification may be different and you should seek out the factory parts book and manual for it!

Also, after half a century in which someone could have altered the internals of your engine to who-knows-what specification, you might want to investigate what parts are actually in it so you can compare it's actual specification to what others and the factory did, which might help you get in the ballpark for jetting etc...

Sorry, my fault for being lazy. I thought Andy might not have the jet etc specs. It doesn't matter what the carb body is numbered (obviously as long as it is the right size). The option twin carb set up has the same spec as I have given. I agree with Ben that this is only a starting point. Fine tuning will need to be considered once she is run in.

Cheers

Alan

Hi Andy

I a have attached page 55 from the parts book, page 57 to follow which might be helpful.

As you can see, Norton did not list any standard way to attach two carburettors to a 99SS head, which has polished 1 1/16" inlet ports with the studs vertically above each other. I expect that the 99 head came with smaller ports than the SS, but it looks like it can be opened up as they share the same casting. The inlet port sleeves listed will only fit downdraught heads. All three 99SS's I have ever seen had only single carburettors and manifolds, and I find it hard to believe that retrofitting single carbs could have ever been that popular!

RGM (I think) offer a twin carb adaptors for our type of heads.

The parts list does not include Amal jet sizes, but they look like Amal part numbers, and it might be possible to cross refer them to a specific throttle slide cutaway using Amal data. Unfortunately it says "Main jet (specify size)" on page 58, so that has to be tuned for the individual bike.

Steve

Andy this is page 57.

I have several of the twin splayed carb manifolds. They come in different sizes! I confirm that RGM do one that is correct for the 99. One is fitted to mine.

Alan

Hi Alan

The $64000 question - is it possible to tell if any of them were originally Norton parts or aftermarket?

It is conceivable that Norton offered twin carbs as an upgrade or option somewhat retrospectively - ie after the 1962 parts list was published.

Annoyingly the list has no publication date, but it would be reasonable to think that it had to go out to dealers at the beginning of the 1962 season, maybe it went to press in late 1961.

To my mind the RGM part has the look of a low volume, aftermarket, machined-from-a-single billet look about it, not like the mass produced Nomad or 650SS (or indeed Commando) Norton solutions. Any chance of a picture of your collection?

Cheers

Steve

Steve

I have had one since the mid 60s but it was second hand and it is for an 88 and won't fit your head. I have always thought it was Norton. I will find time later to take some photos.

Cheers

Alan

Steve Marshall, if you look at page 55 from your own parts book, part# 23739, it says is a manifold for the 88ss and 99ss.

This part did indeed look like a machined block of alloy, and manifolds like it were made and used by Norton to put twin carbs on motorcycles since the 1953 Daytona racers, long before there were any companies like RGM selling replica and aftermarket parts for Nortons. They are a simple part that is easy to replicate. Also of course they were made in different sizes over the years to fit the two different spacings between the studs of early and late Dominator heads.

Your parts list also has a quantity of Four studs to hold the manifold to the head, four studs being needed because it bolts onto the four holes above and below the two intake ports on the back of the cylinder head.

Mr. Marshall, you came onto the NOC message board a short time ago asking questions about your Model 99 Norton, which you knew nothing about. Now a few weeks later you are an expert? You have proven you can not read and interpret parts book informationDid you even find out what model 99 you own yet?

Also just because somebody puts a 50 year old bike up for sale on Ebay and claims it is a 99ss, it does not mean that THEY know what they are talking about any more than you do. Seeing the bike on an Ebay auction does not mean you saw it, or that it even is what the auction claims. Unless somebody has their bike backed up by factory records as a 99SS, and unless it has the "99SS" stamping back by the crankcase breather, then it is not a 99SS.

The Ebay bike you linked to in another thread does not have twin carbs like all 99SS bikes had, it has a magneto which is not correct for a 99ss which should have a coil ignition. It has the wrong speedometer, a 150 mph speedo is spec'd for 1962 SS Nortons. The two 88ss and single 650ss of 1962 in my possession all have this 150mph speedo. So the Ebay bike has been through a bad restoration mill, not even being 99ss colors.

You need to look at Norton Dominators for a decade or two and do some extensive reading on them once you master that skill, then maybe you can come back and offer something of use here. As it is you are misleading people and butchering the history of Norton motorcycles.

Ben, I think your comments are rather harsh but I agree about the manifolds. I had a look through mine. The earliest that I can date one is 1965. That is from a 1954 88 that had been used for club racing in the early 60s. It was my first Norton motorcycle and I acquired it in 1965. The vertical spacing of the holes for the studs on the head is 1.5 in. I have another that is identical but I acquired it later. I have always believed that these are Norton parts. I thought I had one but with 1.625 in spacing for the later head. Can't find it! That also I thought was Norton. The one on my running 99 is an RGM close copy and obviously also with 1.625 in spacing. I tried to upload some photos with good enough resolution to be useful. I failed. To give the purists apoplexy, I should point out that my 99 is a de-luxe, converted to cafe racer, and with one carb from a 650SS, and the other from a BSA sidevalve.

I shall shut up now for a while. I am off south to find some warmer weather.

Cheers

Alan

Yea, my comments were harsh. But this is the NOC website. It should be the one place Norton enthusiasts can go to get accurate information and data they need for their bikes, but unfortunately that is not the case here or on any internet message forum for these bikes......

It is amazing to me how many people think that because something is said on an Ebay auction that means it is true, and because someone has said something on an internet forum it is true. Anyone can go onto any of these venues and put anything they want on there, all they have to do is to be able to read and write, and then not even very well.

I had one guy on one internet forum say that something silly was true because someone on this forum confirmed it, but when I checked that source on this forum they said the information was something they got from the first person! So it was a dog chasing it's tail and total BS.

I almost never tell anyone anything about Norton motorcycles or history unless I can 100% back it up with factory literature or hard parts. If I say something that I heard second hand I will make it clear that it is second hand information or an opinion. If someone proves me wrong then I correct what I have written or said, but I will not back down to opinion or hearsay or someone that has nothing but "it makes sense".

If anyone is serious about the Norton they own then they 100% have to get at least a parts book for it from the year the bike was manufactured. If you get a 1968 AMC parts book and look up parts for a 1962 Norton, then you are not going to get what Bracebridge Street would have sold as a part for the bike, you are going to get what AMC wanted to retrofit it with at that later date, which could be much different than what the bike was manufactured with.

Looking for information to restore or maintain a Norton with on the internet is a complete gamble.

Previously wrote:

Yea, my comments were harsh. But this is the NOC website. It should be the one place Norton enthusiasts can go to get accurate information and data they need for their bikes, but unfortunately that is not the case here or on any internet message forum for these bikes......

It is amazing to me how many people think that because something is said on an Ebay auction that means it is true, and because someone has said something on an internet forum it is true. Anyone can go onto any of these venues and put anything they want on there, all they have to do is to be able to read and write, and then not even very well.

I had one guy on one internet forum say that something silly was true because someone on this forum confirmed it, but when I checked that source on this forum they said the information was something they got from the first person! So it was a dog chasing it's tail and total BS.

I almost never tell anyone anything about Norton motorcycles or history unless I can 100% back it up with factory literature or hard parts. If I say something that I heard second hand I will make it clear that it is second hand information or an opinion. If someone proves me wrong then I correct what I have written or said, but I will not back down to opinion or hearsay or someone that has nothing but "it makes sense".

If anyone is serious about the Norton they own then they 100% have to get at least a parts book for it from the year the bike was manufactured. If you get a 1968 AMC parts book and look up parts for a 1962 Norton, then you are not going to get what Bracebridge Street would have sold as a part for the bike, you are going to get what AMC wanted to retrofit it with at that later date, which could be much different than what the bike was manufactured with.

Looking for information to restore or maintain a Norton with on the internet is a complete gamble.

Hello Ben I agree with you on all your comments . I have a Daytona racing 1954 Dominator model 88 Fitted with a semi close ratio gear box .also I have the 23 tooth Manx gearbox sprocket that came off it and the twin carb Inlet fixings and I have the swept back pipes and rear set for it too , But Now I have rebuilt it back too a standard machine . Maybe I did The wrong thing here . And I have seen this so Called 99ss on Ebay with a Single Carburettor fitted And In The wrong colour black And Sliver . All 99SS where two tone grey . I had one years ago It was a Very Good Machine Too And I still wish my dad had not sold it when I was at sea On the Big oil tankers. of some 250.000 tons now there bigger than this going up too 680.000 tons . I thought the 250.000 tonnes where big enough they twisted and rocked like big jelly's. and in heavy seas they can been very scary too , As the MV Derbyshire Sank with the lost of all hands in the Indian ocean . well back too bikes . I have also the parts Manual For the 1954 Dominator and the Norton Manxman 1960/61 only Parts Number relating too the Norton Manxman only in 1962 these where deleted by AMC trying there best to manufacture Machines as cheaply as they could to compete with other manufactures like Triumph and BSA And Harley Davidson In the USA over there there was a big demand for off road bikes . And thats where AMC went with the Atlas Engined Hybrids. Yours AJD

Hi Ben

Thanks for helping to clear that point up. I am pretty keen to be absolutely certain - as I will feel compelled to acquire the necessary parts to put it back to twin carbs, if a single carb was absolutely not an option when it was sold. Your four stud point is persuasive, as is the fact that p/n 18542, described with gratifying detail as "Inlet manifold (for dual carburetter fixing)" on page 65 cost £1 17s 2d - exactly the same price, to the penny, as p/n 23739.

It would be nice to have a close up pic of the actual installation, and to know whether, as standard, they had handed carbs/ one carb with a cutaway float bowl (or either alternative). BTW is the RGM part effectively the same as the Norton part?

It is probably a statistical freak, but after several hours trying I cannot find a single picture on the internet of anything being described as a 99SS which has a non-downdraught head and yet has twin carbs. Yet I found a few with single carbs - like my own and the one for sale on eBay right now. I have a few books on Nortons and Dominators but they are no specific help either. Of course the 99SS could be a case like the Triumph GP, of which it was said that only 500 were made, from which about 1500 survive, or something like that.

Memories of the sixties were that everybody was converting from single to twin carbs, high lift cams, high comp pistons - it seems that a least few were going in the opposite direction.

Best Regards

Steve

Here are some photgraphs of twin-carb Model 99 Nortons, both taken from Roy Bacon's book on restoration:

http://www.facebook.com/photo.php?fbid=388879567825981&set=a.388879421159329.82306.187441501303123&type=1&theater

http://www.facebook.com/photo.php?fbid=388879537825984&set=a.388879421159329.82306.187441501303123&type=1&theater

Mr. Marshall, did you ever get the factory record for your bike or get a look at the crankcase back by the breather to see if it is stamped "99SS"?

The twin carbs on Norton SS bikes were not of the "chopped" float bowl variety until the downdraught 650 style head was used. The pre-downdraught manifolds used to adapt twin carbs splayed the carburetters outwards in the fashion of a Triumph, so that Amal monoblocs with full float bowls could be used on both sides.

As to your Triumph GP comment. Yes in this day of vintage motorcycles becoming objects of investment and prestige sadly many individuals out there will do whatever it takes to boost their ego or make a few dollars in the hobby.

In the case of the Norton model 99, where a 99ss or a bike shown in the factory records to have originally be fitted with high performance options will offer some bragging rights and financial rewards for the owner, it is easy to find Model 99 Norton owners at shows, auctions and in classified ads claiming their restored bike is a 99ss etc.. So buyer beware, and the same to those looking for information.

I would not buy any alleged Norton 99ss unless it had matching frame and engine numbers, the correct "99ss" stamping on the crankcases by the breather and I had checked it's serial number in the factory records through the NOC and antique motorcycle club. I would also hope that the gearbox and front fork number matched the records.

I would also want to have looked at a number of other Norton SS crankcases so I would be familiar with the font and style of the stamps used at the factory in Bracebridge Street so I could spot re-stamping and altering of numbers.

Errors can be found in any book written, including those on Norton motorcycles. But at least books were written with some effort into their research. All there is on the internet are sales ads, auctions and message boards like this, upon which anyone can say anything at all without any oversight. Even when someone on the internet quotes a supposedly good source of information, the person doing the quoting is very likely to misquote, make errors from memory or even purposely alter or spin things to suit personal interests.

Ben

I have been promised that I am getting my cases back on Saturday, I will get in touch with the Records officer ASAP after that. BTW I have noticed that the stud holes on my 2:1 inlet manifold are suspiciously elliptical - looks like a bit of filing work - suggesting it was not an original fitment.

I doubt the price premium this side of the pond for a 99SS (even now) would warrant too much dishonesty on purely financial grounds, but it could be an ego thing. When I bought it in 1978 they weren't worth that much whatever they were - in fact I remember reading a magazine article about how Manxes and Vincents were getting so cheap that they were becoming affordable street options. The vendor chucked in the original engine for free as I recall.

Thanks for the picture links, shouldn't be too hard to pick up another standard 1 1/16th 376 carb.

This looked like a useful link, if it is accurate!

http://www.britishspares.com/46.

IT bulletin boards often have scores for replies to be scored and note the number of contributions made by the poster FWIW.

The attached pic is from eBay last week - but not the machine discussed previously.

Steve

Hi Andrew.

The 'Norton 1959 Range Price List' (dated November 1958) is reproduced in the letters section of RH264, p.20. It clearly shows twin carbs as an optional extra for both 88 and 99. My own 1958 (year of manufacture) Model 99 (incidentally identified as a '99 Special' on the buff log book) has run twin carbs from new, whether it was supplied like that from the factory or modified at the dealer I couldn't tell you, although I have a factory records certificate from the NOC clearly listing it as a twin carb, which makes me think it probably left the factory like that.

I have owned my bike for five years, the PO had it 45 years and is/was confident the carbs on it were original fitment. They are 376/67s, not handed and identical in every respect. I have actually replaced them this winter, with new units from TMS using the 'book' specs of 250 main, 106 needle, 25 pilot with No.3 cutaway. When I was researching these, I was told not to worry whether they were 67 or 220, the '376' is the important bit. It was suggested that the suffixes were an amal notation to denote fitment to a certain model and that all I needed to do was state which internals I needed. By the way, TMS had these on the shelf whereas Burlen (main agents?!) gave me a four week lead time. The chap I spoke to seemed very knowledgeable too.

The inlet manifold on my bike is as described earlier, ie billet alloy and splayed, and I would guess easily replicated.

Hope this helps

Martin

Hi.

Just to back up Martin Rowe's post - I own a 58 600cc Dommi that was supplied with the optional Sports Equipment. It has been in, first my Dad's and then, my possession since 1964 so it hasn't been buggered about with too much! From the frontpiece of the 1959 Norton Manual - word for word:-

Models 88 and 99 with H.C. Pistons and Sports Equipment

These machines are basically to standard specification except for the following:-

Compression ratio 88 - 9:1 99 - 8.2:1

Twin Monobloc Carburetters Amal 376 to standard settings.

Large Inlet Valve.

Polished Inlet Port and combustion chamber.

The carburetters are not 'handed'. The manifold is similar to that supplied by RGM. There shouldbe heat insulating spacers fitted between the head and manifold.The holes fixing the original twin manifold- as Steve Marshall noted - are (vertically) elliptical. I can only think that this was to allow the original special1/8 WW (spanner size)thick-headed fixingbolts to be inserted asit would be well nigh impossible to get them in if the holes weren't elliptical. Incidentally, my carbs have been bored out at some point during the 6 years prior to us gettingthe bike- has anyone else out there seen similar on these particular bikes?

If you can get hold of a copy, Roy Bacon's Norton Twin Restoration has a good photo of the set up on page 66

Regards.

Ian.

Ian.

First - yep I agree that Ben HAS been a little harsh as I don't think people were claiming that what it said on eBay must be the absolute truth. He's right about errors as there are even some in Roy Bacon's Dominator book! All SS Dommies had twin carbs ex works - in the old days that was the whole point of its appeal to Rockers! Without twin carbs you couldn't call any bike an "SS"! Many years down the line they may have well been "de-tuned" to just one as it's generally easier to maintain. Pre 1960 we had "Specials", which were almost SS spec. They wouldn' have had "SS" stamped on the crankcase. (Not very difficult to punch that on the driving side crankcase anyway!)

My 1959 99 originally had twin carbs as optional extras (confirmed by John Hudson when he was working for AMC in Woolwich) When I bought it in 1965 (only 6 years later) it had been reduced to single carb for sidecar use. The original longer head studs were still used with a single manifold and nuts used as packers to take up the extra stud length! The person who owned it before me was a 'butcher' in that he didn't maintain it and was good at "botching". The bizarre thing is that he was the first owner! I can only hazard a guess as to why he bought it with nearly all the optional extras for 1959 and then ran it into the ground. I bought it from Pride & Clarke as a wreck for £59-10s.

The other option of "polished head" I'm pretty sure included the ports which were probably enlarged at the same time. They also had the later large inlet valves.

There were no handed or 'chopped' Monobloc carbs available until at least the mid-1960s I believe, but I stand to be corrected on that. There were certainly none up until at least 1962. I have original handbooks and Parts Lists for most Dommies from about 1954onwards in original paper form or electronic. I started to collect them justfor interest!The carb setups for single and twin are well documented in most manuals. As has been said, you can use the same internals for single or twin carbs.

Cheers, Lionel

The Norton 650 Manxman had the downdraught head and chopped monobloc carbs as standard.

First despatched from the works in November 1960 for sale as a 1961 model in the United States. An acquaintance of mine bought serial #49 new in early April 1961 at Imperial Cycle Sales in Buffalo New York.

The U.K home market did not see the downdraught head and chopped monobloc carbs until the 88ss and 650ss got them for the 1962 model year.

Thanks for that Ben - it confirms what I said about there being no chopped or handed carbs until at least 1962 in the UK. Cheers, Lionel

Hi Ben

The 1962 parts book and Vic Willoughby's April 1961 road test suggest that the 99SS used the same compression ratio as the 99, while Vic Willoughby notes that the 99SS's were blueprinted to ensure that the compression ratio was accurate.

Steve

Previously wrote:

The carb that Alan listed, the 376/220, is for the 1961-62' 650ss model. The other carb, 376/67 is what was listed on the NON-SS model 99 that came from the works with the twin carb option or as parts over the counter for a dealer or owner to install.

Because the 99SS had higher compression than some of the standard Model 99s, and a more sporting camshaft fitted, it might need a carb outfitted with different jets etc..

My data is taken out of an actual parts book for the 1961 and 1962 Model 99 bikes. If your Model 99 is an earlier model than this, then the specification may be different and you should seek out the factory parts book and manual for it!

Also, after half a century in which someone could have altered the internals of your engine to who-knows-what specification, you might want to investigate what parts are actually in it so you can compare it's actual specification to what others and the factory did, which might help you get in the ballpark for jetting etc...

Andrew, who started the thread and is the one we are trying to come up with information for, is working on a 1959 Model 99 engine, which that year had a std. compression ratio of 7.4:1, and is "some of the standard Model 99s" I was talking in reference to......that is why his and other 99 Nortons with lower compression might indeed need different jetting...... and why I did not say "ALL model 99 Nortons".

By the way Steve, how about those factory records and numbers off your Model 99 crankcases which you surely should have gotten back by now???

Hi Ben

My 99SS was shipped as 'Sports Special Spec, Chrome Guards, Rev Counter, chaincase, despatched on 6th June 1961 in black and cream. Engine number 98046.

Carb spec is not listed.

Dave Catton confirms that 99SS's could be ordered in any colour, the compulsory silver/black combination being a 650SS thing.

Vic Willoughby's April 61 road test of the 99SS says (edited highlights):

"Since the chief item in the earlier sports specification is twin carburettors....choke diameter is 1 1/16"...inlet ports are opened out to suit.....standard pistons are used....also they have the six-fifty's two rate duplex valve springs....both Sports Specials have the Manxman camshaft...flat base followers...the light alloy pushrods are hollow and barrel-shaped with a diameter of 3/8in in the middle."

Other background I think my cases have the 650cc bulges, and the head and barrels are both stamped 'SS'. Unfortunately the crank regrinder built my crank up again and I will have dismantle it to check the size of the sludge trap and ensure it is torqued down correctly. The head and barrels are stamped 'SS' and the cam is stamped 'X1'.

It does seem that in 1961 the 99SS and 99 had the same compression at 8.25 and maybe the same valve sizes, the inlet tracts being opened up slightly on the SS. Were the 1959 pistons dished or were the 1961 pistons domed? BTW mine are flat, but obviously not the originals at +030". By coincidence I once worked for a while at Hepworth and Grandage in Bradford, but they were part of AE by that time.

Steve

John Gregory, who built the Hogslayer drag bike for T.C. Christenson that is so famous now, said when he put Nomad pistons in a 650 it gave him 10.75:1, so the extra stroke was worth .75 points in compression over the 600cc Nomad with it's shorter stroke, which if subtracted from the 8.9:1 of the flat-top equipped 650, would give a 99 right around what the factory said it should have, 8.25:1 with a flat-top. I have a lot of sets of new Hepolite/wellworthy Model 99 pistons laying around here, and every one of them has a dome on top, some look to be standard replacements and three sets are Powermax racing pistons, so it looks like they must be at least Nomad pistons. One set of the Powermax had an even higher dome than the rest of them. Here in the United States, I have never seen new flat-top 99 pistons laying around, just some old used ones taken out of early engines. Fits right in with the American thirst for power......it does not look like anyone wanted flat tops in their engines. I have taken apart more than one old 650 engine that had been fit with modified, domed 99 pistons somebody had installed per the John Gregory suggestion...

Thanks for confirming that Ben, I am very happy to stay at a ridable 8.25:1.

I think I have pretty much everything I need to complete the bike now, tacho and all.

I mostly ride a S*z*k* SV650S and when I think about it just about the only time I go above 6000RPM is to terrify nieces occasionally. So with the wisdom of age I reflect on what is the point of having less torque low downin exchange for potentially more maximum power in a rev range you hardly ever use? Inevitable conclusion - I am losing my personal thirst for power.

Steve

Previously wrote:

I have checked the Norton 1962 parts list at some length, and all the twin carb options are very specifically only for the 650SS and the 1962 88SS.

The earlier Nomad had a twin carb option with tubular stubs (see pic) and there were (and still are) twin carb adapters available for non-draught heads in the form of single alloy billets.

It has been said that all SS Dominators came with twin carbs, and I am virtually certain that is not correct in respect of the 99SS and 191 88SS. In fact I cannot find any documentary evidence suggesting that it was ever a catalogue option for the 99SS at all. If you have anything I would be very interested to see it. There is a 99SS with a single carb on eBay right now with good close ups.

Best Regards

Steve

For those interested, here is a link to a company that sells the Nomad Intake stubs:

http://www.eurojamb.com/norton-600-nomad-intake-manifold-set-88-99-dominator-p-1963.html

Brand new production, exact copies of the twin manifolds used on the limited-production Norton Nomad. They are also suitable for early vertical-stud intake ports of Dominator heads, for twin TT carb use.

Skip

Previously wrote:

Previously wrote:

I have checked the Norton 1962 parts list at some length, and all the twin carb options are very specifically only for the 650SS and the 1962 88SS.

The earlier Nomad had a twin carb option with tubular stubs (see pic) and there were (and still are) twin carb adapters available for non-draught heads in the form of single alloy billets.

It has been said that all SS Dominators came with twin carbs, and I am virtually certain that is not correct in respect of the 99SS and 191 88SS. In fact I cannot find any documentary evidence suggesting that it was ever a catalogue option for the 99SS at all. If you have anything I would be very interested to see it. There is a 99SS with a single carb on eBay right now with good close ups.

Best Regards

Steve

For those interested, here is a link to a company that sells the Nomad Intake stubs:

http://www.eurojamb.com/norton-600-nomad-intake-manifold-set-88-99-dominator-p-1963.html

Brand new production, exact copies of the twin manifolds used on the limited-production Norton Nomad. They are also suitable for early vertical-stud intake ports of Dominator heads, for twin TT carb use.

Skip

Hello There Not The Original ones these were made in brass I have a pair Yours Anna J

Atthe first rebuild of my 1959 99 'Special' in 1965, I bought what were listed as 9:1 pistons (Hepolite). They have domed tops but as you all know a 1959 model would have had 8.2:1 as high compression pistons - as per the Maintenance manuals of the period. As I've said elsewhere, don't get too hung up on precise compression ratios down to decimal points because, if you have a re-bored barrel, the ratios will be different. A simplistic explanation is; bigger bore = bigger swept volume = higher C/R as the combustion volume will be substantially the same. Obviously engine capacity increases too. A +.040" rebore is about 1mm increase in bore diameter. (Arguably it is EXACTLY 1mm increase as pistons/bores are sized in mm in UK & Europe and nearly always have been!)

As far as the original question about carbs goes, the best way is to consult the carburettor "Oracle" - Amal who produce a lovely FREE reference catalogue and CD with the carbs and settings for hundreds of bikes! Also online I believe. The carb Number is usually listed as 376/220 for 99s with twin carbs, but the important part is the '376'. Amal give the jettings and components for all thevariations of engines, with the exception of choke cutaways. Twin carbs are normally two of the same carbs as usedwith a single carb setup, as has been said and is clearly documented in the Manuals. Interestingly (and news to me but not to experts) is that the 600cc Nomad uses twin 276 carbs.

I have quite a collection of Norton Twin Manuals and Parts List books from 1949 to around 1967. I would be happy to look up specifics for anyone, but not scan or photocopy everything! I do have a fair amount on CDs too which I've bought through eBay.

Cheers, Lionel

Atthe first rebuild of my 1959 99 'Special' in 1965, I bought what were listed as 9:1 pistons (Hepolite). They have domed tops but as you all know a 1959 model would have had 8.2:1 as high compression pistons - as per the Maintenance manuals of the period. As I've said elsewhere, don't get too hung up on precise compression ratios down to decimal points because, if you have a re-bored barrel, the ratios will be different. A simplistic explanation is; bigger bore = bigger swept volume = higher C/R as the combustion volume will be substantially the same. Obviously engine capacity increases too. A +.040" rebore is about 1mm increase in bore diameter. (Arguably it is EXACTLY 1mm increase as pistons/bores are sized in mm in UK & Europe and nearly always have been!)

As far as the original question about carbs goes, the best way is to consult the carburettor "Oracle" - Amal who produce a lovely FREE reference catalogue and CD with the carbs and settings for hundreds of bikes! Also online I believe. The carb Number is usually listed as 376/220 for 99s with twin carbs, but the important part is the '376'. Amal give the jettings and components for all thevariations of engines, with the exception of choke cutaways. Twin carbs are normally two of the same carbs as usedwith a single carb setup, as has been said and is clearly documented in the Manuals. Interestingly (and news to me but not to experts) is that the 600cc Nomad uses twin 276 carbs.

I have quite a collection of Norton Twin Manuals and Parts List books from 1949 to around 1967. I would be happy to look up specifics for anyone, but not scan or photocopy everything! I do have a fair amount on CDs too which I've bought through eBay.

Cheers, Lionel

Hi Anna,

these are exact copies of the NOMAD stubs which were not brass, but are suitable for dominators:

Brand new production, exact copies of the twin manifolds used on the limited-production Norton Nomad. They are also suitable for early vertical-stud intake ports of Dominator heads, for twin TT carb use.

Hope that clears thing up,

Cheers!!

Skip

I managed to obtain a pair of 376's that originated on a 99SS, now my problem is getting hold of a 99SS manifold. Mick Hemmings will machine one out of a billet for well into 3 figures (£s) and RGM offer one which they say is only suitable for studs in a line (while their picture indicates the opposite - as attached.

Would any kind person put up a close-up photograph of a genuine Norton pre-downdraught 88SS or 99SS manifold for me so I know what I am looking for?

Thanks

Steve

One on the left definitely Norton. I bought one from RGM for my 99 and it was perfect (didn't have RGM on it).

Nice manifolds Alan. What is the spacing between the mounting holes on these? The dirtier one looks to have more precise and smaller mounting holes drilled....

Thanks Alan, extremely helpful - I got to talk with RGM yesterday and they got one down off the shelf and conceded that they are indeed made for heads with studs vertically above the other. Your pics show that they are practically identical to the originals + a balance pipe in your case, so problem solved - using that most versatile of all Norton service tools, the wallet.

Only slight problem is that they measured the tract diameters at about 0.98" so I will need to take 1/32" off all round. Might accidentally remove the RGM logo too....

Ben, both of these are 1.5 in spacing and so are for the earlier head. The one on the right has been badly treated at some time in its past and the holes have been enlarged.

Right. So Andrew Jarrett's 1959 engine would probably need the 1.5" manifold, if in fact it has the correct head, and Mr. Marshall's slimline 99 should need the 1.625" spacing, and that late manifold might easier accept carbs with a bore larger than 1". I would not buy one from RGM for a 99ss if all they have is the 1.5" manifolds. Run the bike with the single carb setup until the right part can be found used somewhere.

The one I bought from RGM had 1.625" spacing.

As has been said, from about 1958 99s were available with twin carbs whilst still using a standard, non-downdraught head. My 1959 99 was a "Special" with factory extras including twin carbs, larger inlet valves (like 1960 onwards) silver and black paintwork, chrome mudguards, full rear chain enclosureand H/C pistons (which were9:1 at this time). All these options are well documented in the parts books. For 1959 (PS206) they are printed in red at the end of the book. Amongst the listed options that mine didn't have included an air cleaner, crash barsand folding kickstart. I now have crash bars and folding kickstart but not an air cleaner because I don't know what type will fit through the hole in the plate behind the carb. (I'm sticking with the single carb - sorry!). The oil tank has studs, which I assume are for an air cleaner body, so I'd guess a tube attaches to the carb and passes through the hole to the cleaner.

By the time I bought it my bike had been detuned to single carb, so I have no idea what the twin inlet manifold looked like for the non-downdraught head with vertical studs. All my technical info about it was gleaned from John Hudson by writing ("snail mail" !) to him at the factory, which by this time was at Woolwich.

Cheers, Lionel