Amal Twin Carb's

... have a chopped monobloc, ie the version with the float chamber slimmed down till virtualkly non-existent? Burlen have them: http://amalcarb.co.uk/chopped-1-1-16in-monobloc-carburettor.html

The 99 Model big-valve heads that had the twin carb manifold were usually fitted on the S and SS models were fitted with two standard 376 AMAL Monobloc carbs that had a float chamber on the left-hand side and the adjustment screws on the right.  The 88 Model big-valve heads also used this twin carb manifold primarily on the S, SS and options on others.  When the Semi-downdraught cylinder head was adopted on the 88SS then like its bigger brother 650 the right-hand carb had its float chamber chopped and a link was made between the main jets via a banjo on an extended jet holder at the bottom of the carbs.   For racing, where one float chamber was not considered of sufficient quantity, a carb with a right-hand float chamber was developed but these tended to be in the 389 (689) size ranges.  If you have a 99S or 99SS head then  keep both carbs and occasionally give it a squirt - you'll see why two are better than one......Cheers, H 

I had one of those splayed manifolds on my  hotted up 61  88, with two standard 376 carbs ,an SS cam and HC pistons  , It was a pig to get at the carbs  but  kept up with the mates pukka 99SS and 650ss.  A very underated machine the 88SS.  Wish I had it now.

If you like John -- But I should only go that way with a semi-downdraught cylinder head.  Make sure that both carbs match the inlet ports .    Cheers, H     

My 88SS has the downdraft head. But many years ago on one of the first VMCC Relay Rallies I encountered a chap with one of the earliest few 88SS which had the predowndraft head. (at Aldermaston I think...was it someone here?)

Anyway we met up on the road. He sat bolt upright and his bike definitely had better legs than mine! Plumstead Norton changed camshafts at about the same time as cylinder heads  and I wonder if by making two changes at the same time they obscured the fact that the new cam made more difference than the new head?

Many people did swear by the SS camshaft stamped with X1 ( a hardness rating ).  The X2 cam that was fitted at Plumstead  did wear out quickly even though the hardness was deeper ??  Cheers, Howard

... a finned float extension in my pile of Amal bits if it's any use to you?

Standard Monobloc carbs were used as twin carbs on the 99 up to 1959 as I have one.  I have a post elsewhere with more detail, but handed Monos weren't made then.  They had a splayed twin inlet manifold to accommodate the float chambers.  The Norton Parts List for 1959 has twin carbs in the "Optional Equipment section in red type at the back.  You needed two Part No. 22113.

My 1961 99SS came with twin monoblocs and had the splayed manifold as well.

New ones can be obtained from Burlen. I had a pair for a twin monobloc Atlas a while ago. I did have to add my own float bowl extension from the old pair.

To me, they are in the same group of bits as finned rocker covers - Items in the 'go faster goodies' section that don't actually do anything useful.

I've never had nor wanted an extension on my 650, and it still runs happily up at the top end, no sign of fuel starvation. They were never fitted as standard to any bike, even to Atlases which had way bigger main jets than the smaller bikes in the range.

Just saying..

Regards,

George

The Box filter that lives between the oil tank and battery is (or was) availiable from Norville . I have one on my 99.  Its not a very impressive thing needing a bit of re-shaping to fit. A ring on the carb accepts a rubber connector (a bit too loose) that connects to the box. The filter can be constructed from half an Austin Mini filter with some mastic to seal. The box needs painting. Its a very tight fit to the outer flange of the oil tank . 

I certainly remember fitting a pair of matched 389/689 to a 650SS in the 1960s.  I don't think that there was ever a matching 676 variety with right-hand float. They did make a difference flat-out on the back straight at Aintree.   Cheers, Howard 

The box filter bolts to the back of the oil tank using the threads already there. It would be impossible to fit with the battery box in position.   Having used both Monoblocks and concentrics I view the mono's as superior in all respects.

Did you mean a monobollock with the floatbowl on the right? There were a left/right pair on ebay recently. Didn't Triumph use them at one time? As for a chopped 376 as per 650SS, have a look at:

http://amalcarb.co.uk/monobloc-series/376-series/base-line-specifications/chopped-1-1-16in-monobloc-carburettor.html

Not good news for Atlas owners though - the chopped 389 isn't listed anymore.

Worst thing re: twin carbs (pre-concentric ones) is accessing the air adjuster screw on the left carb.

As for my comment earlier regarding the float bowl extension, I see Amal have 2 types available - one plain and one finned for even more speed!

Regards,

George

The 389LH/689RH were for the most part 1966 only. Approximately 150+/- models of 389 and only about 15 LH/RH sets, of which a few were for atlas and the hybrids.  BSA A65.....etc.

around 1967 started concentrics

Dave

63 Atlas

66 Atlas 389/689

68 Dunstall Atlas

Simply put monoblocks flow more air for a given size wrt concentrics, and they didn't wear out so fast.

George

make a 3 slide into a 3 1/2 by filing 1/32" from the cutaway.

My understanding is that each whole number is equal to 1/16". Easy to check with your new slides - is the cutaway height 3/16"?

I would suggest caution however - the suggested carb specs/settings given for 50 - 60 year old bikes were for the fuel used 50 - 60 years ago, not the stuff we are using nowadays, so you may well find that you will need to adjust/change settings to make it run right, more so as from your other posts you are possibly building a 'mongrel'.

Regards,

George

You can file the bottom of a slide to make a 3 from a 31/2 but it needs to be done well. The needle position will also change. Monos last better (with a chromed slide) they are easier to access the jets at the roadside and the single carb float. Look better,  Are more original on most Dommies.

I used to race on a single carb 88 and did ok. I'm not convinced that twin carbs are a real benefit - except possibly at full throttle above 7,000 rpm.

The Altas engine in my Domi 99 came with handed 389 carbs. I promptly opted for a single carb manifold as I am too idle to faff around with adjusting 2 carbs and throttle cables. It still goes rather well which is fine by me. And I have a spare carb ready to fit should I need it.   

Huricanes in North Africa had field-made air filters fitted using sanitary pads. There was chaos when supplies of pads were stopped as someone back at home saw that there were no WAAFs in North Africa so stopped sending pads. Hurricanes were eventually fitted with proper Vokes filters...