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Lumpy SC at low revs

racingred

PCGB Member
Member
Hi. My friends SC is very 'lumpy' at low revs but appears to clear at around 2500rpm...I understand it did have new plugs and dizzy cap but this has made no difference. He was going to get a new set of leads next but I was wondering if it is the fuelling side...any thoughts/advice welcome....
 
I had to change all the plug leads on mine - they are screened and they break down inside; whether this causes lumpy running, I'm not sure. I also replaced the auxiliary air valve - apparently (according to a Service Note I have) the early one can open uncontrollably at low partial throttle opening and cause the engine to "buck".
Also, it could be a fuelling problem - ethanol absorbs moisture which can condense in the tank, so you might get a fuel pick-up problem. I use a fuel additive to compensate for the low octane.
Hope this helps.
 
Ignition and vacuum leaks are the common cause. Make sure none of the pipes have fallen off or cracked. If its backfiring it could be the warm up regulator.
 

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