Talkwrench Posted April 7, 2014 Share Posted April 7, 2014 I'll try posting here as SU carbs are common throughout the triumph range. I have a 2500 6 cyl in my little herald and it has a set of 1 3/4" SUs fitted. For some reason the front carb will only run if the fuel adjustment nut is all the way up , even then it's slightly rich? I'm using a vacuum gauge, unisyn and gunson colortune to check. The slides flick up and down ok, could I have two different needles?.. Quote Link to comment Share on other sites More sharing options...
npanne Posted April 7, 2014 Share Posted April 7, 2014 One thing I found when researching these carbs is that, if fitting to a small chassis car (well, at least if fitting to a Spit / GT6), you need the float chambers to be different - one sits higher then the other to compensate for the "nose up" angle of the engine.I'll try to find the thread on here - someone explained it very well. Quote Link to comment Share on other sites More sharing options...
Clive Posted April 7, 2014 Share Posted April 7, 2014 could be the float level in the float chamber. If too high may cause this issue?IIRC there are different float chambers available too. And really digging in my memory, a specialist posted something about using different float chambers for the front and rear carbs in a Vitesse(what your car effectively is) and GT6. I think one was a spitfire float chamber.....I am sure somebody with a better memory and more knowledge will confirm or elaborate :) Quote Link to comment Share on other sites More sharing options...
Clive Posted April 7, 2014 Share Posted April 7, 2014 Ha! great minds and all that 8) Quote Link to comment Share on other sites More sharing options...
npanne Posted April 7, 2014 Share Posted April 7, 2014 http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl?m-1360670248/s-0/highlight-HS6/#num0 Quote Link to comment Share on other sites More sharing options...
piman Posted April 7, 2014 Share Posted April 7, 2014 Hello Talkwrench, apart from the float level (easily checked by removing the dashpot and piston and looking into the jet, you should see fuel about 1/8" down the jet) make sure your choke is not stuck on that carburettor, i.e. the base of the jet should be hard up against the adjusting nut, if not you can set the nut where you like and it will make no difference to the mixture.Alec Quote Link to comment Share on other sites More sharing options...
Talkwrench Posted April 8, 2014 Author Share Posted April 8, 2014 Ok I'll check this and work from there. IF its is to do with the float levels would it still be ok to run like this or am I always going to get one running richer through the entire range? Quote Link to comment Share on other sites More sharing options...
piman Posted April 8, 2014 Share Posted April 8, 2014 Hello Talkwrench, float level is critical and if badly wrong will make tuning impossible.Alec Quote Link to comment Share on other sites More sharing options...
Talkwrench Posted April 9, 2014 Author Share Posted April 9, 2014 Ive attached pictures of front and rear carbs. After reading about the need for different float bowls to compensate for the tilt of the motor it becomes clear, and more-so as Alec said about seeing the fuel height in the jets they simply wont balance, as you can see in the pics one jet up for the front carb and down in the rear carb, more to where it should be.. My question is ..Is it all possible to alter the heights of the floats to compensate [obviously not as good as new float bowls]? I would imagine dropping the front a fair bit, is it likely to run short of fuel?? If not this fix where will I find the bowls? Quote Link to comment Share on other sites More sharing options...
piman Posted April 9, 2014 Share Posted April 9, 2014 Hello Talkwrench, it's fairly easy to adjust the float level down by adding a washer(s) under the needle valve, this has the effect of lowering the level.Alec Quote Link to comment Share on other sites More sharing options...
Talkwrench Posted April 9, 2014 Author Share Posted April 9, 2014 I'll pull the top off on the weekend and see what's there, guess it won't be the early style so adding washers will be the go! Quote Link to comment Share on other sites More sharing options...
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