Sounds like a classic case of Zenith Warp to me, try filling in the jet as
"Richard Brookman" <firstname.lastname@example.org> wrote in message
S2a, 2¼ petrol, 70K miles.
I fitted a new "Zenith" pattern carb (from Craddocks) about 2000 miles ago.
Since then she has run perfectly, with plenty of power, a smooth idle hot or
cold, and economy improved from 14mpg to about 20. So far, so good.
Yesterday, the idle speed dropped to almost zero (I had it set to where the
charge light would just flicker) and today she refuses to idle at all.
Increasing the idle speed a fraction kills the engine dead. Moving the idle
mixture screw in and out makes no difference (until you take it right out,
when the engine stops, obviously). Normal speeds, the engine runs fine as
before. Nothing loose, fallen off or obviously broken, vacuum advance pipe
is in place, and I've done nothing to it except drive around. I'm guessing
either an air leak on the inlet side or a blocked idle jet, but I thought
I'd see if anyone had any bright ideas.
One other symptom, which has developed at the same time: the exhaust has
always popped a bit on a steep downhill on my way back from work, but now
it's popping regularly and loudly even slowing down for junctions. This
suggests an air leak on the exhaust side. New exhaust fitted about 2000
miles ago, but again no problems until yesterday.
Anyone put two and two together and make SQRT(25)? I'll strip and clean the
carb at the weekend otherwise, but since it was 100% OK before yesterday I
reckon it must be something silly.
Pas d'elle yeux Rhone que nous