twin carb...

[callyspoy]

hi friends. hahaha! i did it! silly boy, couldn't help myself! well, i wish i had stopped myself...my twins are waaaaaaay out! thought it would be a little experiment, but i was drastically wrong, it has turned into a mini nightmare!
tickover...shocking, i mean it must be up to about 2500rpm!
driving...not too bad, accelerator cable is stiff though due to being double sprung loaded!
so...i am confused...i had probs with my single carb before, it was pants under load, this time, its okay when under load, but is shocking when idling...please, once again, bail me out! i know a rolling road visit will be in order at some point soon, but does anyone have a short term quick fix to get me by until i do that??!!
thanks for listening to my ramblings, and again, please help!
*Callum*

[bmcecosse]

Post up in 'mechanical' - but sounds like they need a good setting up - and maybe they need overhauling. Twin carbs are really not worthwhile on an otherwise bog standard engine

[eastona]

I agree with BMC.

a good start is to take the dashpots off. check they've got the same needles in. use a vernier calliper to check the jets are level the same amount beneath the bridge. (I think 1.8mm is a good start IIRC)

pop the dashpots on, check they've got oil in.

start up and warm engine

slacken the interconnection and balance the carbs, use a meter or failing that the length of hose method

tighten the interconnection

innevitbly reset idle afterwards

set the mixture using a gas analyser, or failing that, the best idle or seat of the pants method.

reset idle.

One problem I had is If they work well at WOT but are rich at idle, but in order to idle properly they are horribly lean at WOT then the jets could be worn. Or the butterfly spindle could be worn.

With twins, you've got more than twice the trouble, not only two carbs to set up, but they've got to be set up the same.

Not worth the hassle really. IMHO

Andrew

[picky]

fit the single carb back on and fiddle with that until it works ok. check all the points mentioned above, and make sure you have a fuel filter fitted somewhere. the is a very good haynes manual on SU carbs, have a look on ebay maybe?

Picky