SU carb

If the bike runs really well as it was when you first fitted the carb, maybe a colder plug might be an idea?

Hi I have the same setup on my 1972 Roadster. It also runs a bit lean, which is good for riding in town, and at lower rpms. All I had to do get the mixture spot on was to fit an airfilter, which normally requires araised jet seat.On the SU carb you actually lower or raise the needle seat to allow more or less fuel running through!On an HIF carburettor the mixture adjustment, i.e. seat lowering or lifting,is by a cross head screw situated in a recess in the base of the body. You may also want to the check or change the oil (SAE20)in the dashpot,thedamping device in the throttle.A colder plug may work, but it could also cause fooling at lower rpms. I will try and check the needle markings next time I look at my SU carb.

Disregard above, I misread your initial post, I now see that did mention lowering the "needle jet".

Hi

to get su carbs to run richer after idle positions try changing spring weight

from your 4.5oz red spring to a 8oz yellow or run better fuel if not already

super unleaded etc as this mod was around when we had lovely leaded fuel

4 and 5 star.

Mick.

Hi Phil,

I have two Commando'srunning SU's, both appear to run a little lean when looking at plug colour etc, however, one has done over 30,000 miles with this set up with absolutely no problems, I set the ignition timing as advanced as possible without the engine pinking. (ie if you get a pingunder hard acceleration slightly retard the ignition untill it's happy) This method has served me well for many years now & an SU would still be my first choice of carb for a Commando, you can get more or less Interstate mileage with a Roadster tank !

Hope this helps,

Regards, Tim

I have an SU fitted to my 1972 Commando 750 along with a Pazon Ignition System. The cylinder head has been converted to use un-leaded fuel.

This combination works really well and gives very easy starting, a quick warm up and unbelievable miles p/g. Around 65 mpg when cruising at 70mph.

My exhausts pipes have gone totally blue/grey due to the weak mixture but the Champion N7Y plugs are looking fine.

I find that running on cheap, standard un-leaded petrol gives lumpy running at idle speeds. The motor also pinks a little when accelerating hard. Adding a little Octane boost to each tankful helps overcome this. On Paydays I top up with premium un-leaded. I used to add some Upper Cylinder lube or Lead sub every now and then but found that this coats the plugs with a residue that caused a misfire.

The only drawback of the SU is the need to top up the Damper' pot with oil every 1000 miles.

Hi Tim

I I've just read on another Norton site you have some set information on the Pheonix carb kit

please can you help me out

Ta Mick

Hi Phil,

I have two Commando'srunning SU's, both appear to run a little lean when looking at plug colour etc, however, one has done over 30,000 miles with this set up with absolutely no problems, I set the ignition timing as advanced as possible without the engine pinking. (ie if you get a pingunder hard acceleration slightly retard the ignition untill it's happy) This method has served me well for many years now & an SU would still be my first choice of carb for a Commando, you can get more or less Interstate mileage with a Roadster tank !

Hope this helps,

Regards, Tim

Hi Tim

I I've just read on another Norton site you have some set information on the Pheonix carb kit

please can you help me out

Ta Mick

Hi Mick,

I'll try, what do you need to know? I have the original fitting & set up note supplied with the phoenix kit which I can email you, you can PM me from the other site with your address, not sure if that's possible on here just yet. The SU is simplicity it's self, provided you have somewhere near the correct needle & spring, (BFD needle & 4/2 oz red spring) the rest is just adjusting to your engine & use. Float level is critical, if it's too low it will run very weak, too high & at best it will bog at idle, at worst it will piddle fuel from the overflow & always use either 20/50 or straight 50 oil in the dash pot, anything thinner will just not work with the heat generated under a Commando tank & will dissapear very quickly, requiring regular refilling, not easy on a Commando, I get around 1500 miles before needing to top up with 20/50, can be as low as 200 with SAE20! A syringe & length of washer tube makes topping up the dash pot less of a chore.

Hope this helps, let me know if you need anything further'

Regards, Tim

PS, Sorry it's taken a while for me to reply, I had to find my specs to see what I was typing

Previously mick_green wrote:

Hi Tim

I I've just read on another Norton site you have some set information on the Pheonix carb kit

please can you help me out

Ta Mick

Hi Mick,

I'll try, what do you need to know? I have the original fitting & set up note supplied with the phoenix kit which I can email you, you can PM me from the other site with your address, not sure if that's possible on here just yet. The SU is simplicity it's self, provided you have somewhere near the correct needle & spring, (BFD needle & 4/2 oz red spring) the rest is just adjusting to your engine & use. Float level is critical, if it's too low it will run very weak, too high & at best it will bog at idle, at worst it will piddle fuel from the overflow & always use either 20/50 or straight 50 oil in the dash pot, anything thinner will just not work with the heat generated under a Commando tank & will dissapear very quickly, requiring regular refilling, not easy on a Commando, I get around 1500 miles before needing to top up with 20/50, can be as low as 200 with SAE20! A syringe & length of washer tube makes topping up the dash pot less of a chore.

Hope this helps, let me know if you need anything further'

Regards, Tim

PS, Sorry it's taken a while for me to reply, I had to find my specs to see what I was typing

Hi Tim

Thanks for reply, my set up is the phoenix one and runs well but find it a sod to start not sure if my choke cam or fast idle is set

correctly ie clearance between cam and adjuster ? would love a copy of the set up note my email is michaelgreen888@btinternet.com

many thanks Mick

Mick, fwiw when I had an SU fitted I also had occasional problems starting, I found it easier if the carbwas run dry before putting the bike away.

Regards

Mike

Hi Mike,

Will email youcopies of the Phoenix instruction sheets but Iâve found that, assuming floatlevels are correct, difficult starting is usually down to poor fuel flowthrough the petrol taps. When I first fitted mine, the only way I could get thebike to start from cold was to squirt some petrol into the air intake ordribble a little into the plug holes, replace the plug quickly & it wouldthen fire up first kick & run perfectly. Warm or hot starting wasnât quiteas bad, but not brill either. I did some research & found others werehaving the same problem & that fuel level in the tank had a bearing on howdifficult starting was, i.e. a full Interstate tank would start better than ahalf full one & a nearly empty Roadster tank wouldnât start at all. Ifigured it must be down to the head of fuel at the carb so checked through mysystem & found that the taps were quite restrictive, the hole through thecentre part was very small & didnât fully line up fully with the holethrough the body. I modified the taps to have a good 3/16 bore all the waythrough, easily done with a sharp drill bit, & have had pretty much firstkick starting ever since. Subsequently, Iâve modified/changed the taps onothers SU converted bikes & cured difficult starting for them. You wouldthink that once the float chamber was full that would do but it seems there isinsufficient pressure to make the cold start system work properly if thereâs arestriction in the fuel supply, generally SUâs are supplied fuel from a pump inmotor applications so I guess delivery pressures are going to be quite a bithigher than with a gravity feed system as on the Commando & this apparentlyeffects the efficiency of the system.

Hope this helps,

Regards, Tim

there's alsoa Haynes manual coveringSU Types H, HD, HS & HIF(ISBN 1 85010 506 5).

Topping up the dashpot is important, iirc it will run leaner if empty, it does give great aural satisfaction on the overrun, (witha pair of RGM's straight thru Black Cap,sNellie used to set all the car alarms off in mine street, they were glad when I moved

Mike

Hi Guys,

Have been reading your thread ref SU HIF6 carburettors with great interest, as I have one,supplied to me back in 1986by Phoenix Motorcycles, (it even came with a note, signed personally byBernard HOOPER!)

The SU is currently fitted to my '77 Mark 111 Interstate, as was the case when I first purchased the kit.

I agree with all your comments entirely - in particular, the problems with (mainly) cold starting. Yes, it would appear that the fuel level in the tank dictates whether /whether not the bike will start.

So, I too did (quite extensive) searching and trawled the 'net. What I searched for, was if anyone made a manual fuel primer for the SU - Result!!! In the USA a company called Rivera Primo (Harley Specialists) do an SU carb. conversion for older Harleys. They had exactly the same problems kickstarting the Harleys as we have with the Nortons. So they came up with a manual primer/tickler pump, which fits into the float chamber overflow hole on the side of the SU. It is necessary to machine thehole in the carb to accept the spigot tube of the tickler pump. I.I.R.C the spigot is 1/4" in diameter, so the hole in the carb will need to be 0.001"smaller than the tickler pump spigot. My carb was modded by my local Brit. bike engineer, Steve McFARLANE in Cardiff. The tickler should be a 'press fit' in the side of the carb; Steve fitted it for me with 'Loctite' to secure it.

I sourced my tickler/primer pump from Burlen Fuel Systems of Salisbury, UK; their reference part number is (was) RE-TP-1. The pump is compact, nicely made from brass and fits neatly onto the SU withoutspoiling (in my view) the look of the carb; it sort of blends in and looks right.

All you do to start is, turn your fuel tap on, give the pump 6 to 7 presses and it starts really easily when cold, it's never failed. (It's exactly the same idea as my Briggs & Stratton lawnmower engine primer start function!!!) The tickler pump retains the function of an overflow pipe for the float chamber, should it flood due to debris trapped in the float needle.

Have a look at the following sites for further information :-

www.riveraprimoinc.comCheck out 'Eliminator' 1 and 11Carburettors (Parts Lists)

www. patentgenius.com/patent4228110.html (Refers to US Patent design for tickler/primer pump.)

I also found a video clip on 'Youtube' featuring something on the lines of 'Kickstarting an old Harley' - the bike had an SU carb with the same primer/tickler pump fitted.

Finally, I got the idea about fitting a primer/tickler system from an article I'd read in a very old edition of 'The Classic Motorcycle' magazine, December 1999 - Pages 48 to 53 refer.

Hope this helps; I reckon this is the definitive answer to the SU starting problem!!! Ken Weeks

Hi Guys,

Have been reading your thread ref SU HIF6 carburettors with great interest, as I have one,supplied to me back in 1986by Phoenix Motorcycles, (it even came with a note, signed personally byBernard HOOPER!)

The SU is currently fitted to my '77 Mark 111 Interstate, as was the case when I first purchased the kit.

I agree with all your comments entirely - in particular, the problems with (mainly) cold starting. Yes, it would appear that the fuel level in the tank dictates whether /whether not the bike will start.

So, I too did (quite extensive) searching and trawled the 'net. What I searched for, was if anyone made a manual fuel primer for the SU - Result!!! In the USA a company called Rivera Primo (Harley Specialists) do an SU carb. conversion for older Harleys. They had exactly the same problems kickstarting the Harleys as we have with the Nortons. So they came up with a manual primer/tickler pump, which fits into the float chamber overflow hole on the side of the SU. It is necessary to machine thehole in the carb to accept the spigot tube of the tickler pump. I.I.R.C the spigot is 1/4" in diameter, so the hole in the carb will need to be 0.001"smaller than the tickler pump spigot. My carb was modded by my local Brit. bike engineer, Steve McFARLANE in Cardiff. The tickler should be a 'press fit' in the side of the carb; Steve fitted it for me with 'Loctite' to secure it.

I sourced my tickler/primer pump from Burlen Fuel Systems of Salisbury, UK; their reference part number is (was) RE-TP-1. The pump is compact, nicely made from brass and fits neatly onto the SU withoutspoiling (in my view) the look of the carb; it sort of blends in and looks right.

All you do to start is, turn your fuel tap on, give the pump 6 to 7 presses and it starts really easily when cold, it's never failed. (It's exactly the same idea as my Briggs & Stratton lawnmower engine primer start function!!!) The tickler pump retains the function of an overflow pipe for the float chamber, should it flood due to debris trapped in the float needle.

Have a look at the following sites for further information :-

www.riveraprimoinc.comCheck out 'Eliminator' 1 and 11Carburettors (Parts Lists)

www. patentgenius.com/patent4228110.html (Refers to US Patent design for tickler/primer pump.)

I also found a video clip on 'Youtube' featuring something on the lines of 'Kickstarting an old Harley' - the bike had an SU carb with the same primer/tickler pump fitted.

Finally, I got the idea about fitting a primer/tickler system from an article I'd read in a very old edition of 'The Classic Motorcycle' magazine, December 1999 - Pages 48 to 53 refer.

Hope this helps; I reckon this is the definitive answer to the SU starting problem!!! Ken Weeks

I have had a SU fitted to my Harley for the past 30 odd years, It work great. The pump you say you had fitted is stock on the Rivera item, but it can be substituted by fitting a small plastic pipe instead. If you blow a small mouthfull of air into the pipe it pressurises the float chamber just as does the pump. If this works, then you can try fitting the pump after.

Burlen has a very helpfull chappie on the end of the helpline phone. They really do know what they are talking about, unlike us idiots!