"popping" and jerky on over-run

He must only have been referring to the CO, as if this is low the HC will be high. But that's not tested on an older car.

Has it got some sort of valve that opens under high vacuum? Was a common thing to decrease HC output on the over-run by letting in air. Might be a valve in the butterfly or somewhere on the inlet manifold. I'd guess it's not operating correctly - a clean might be all it needs.

Doesnt popping on over run mean slightly lean mixture on over run ?

There are a series of "progression" jets or drilling that are supposed to smooth the transition from idle to main jets - I think these can be partly blocked and account for the lumpy pickup on light throttle openings. To fix this can be awkward - if you're lucky a strip and clean may do it - worst case requires drilling out the plugs that blank of the small drillings etc etc etc.

Steve PS. Is it a capri ? PPS. Yes I did used to have one :-) Cheapest motoring I've ever had......

Often a sign of an exhaust manifold crack or leak.

Dave Baker - Puma Race Engines

I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though.

The message from snipped-for-privacy@aol.comma (Dave Baker) contains these words:

Certainly something that's making it run lean on overrun. Either what Dave says or a blocked jet - or you've tried too hard to be a miser!

Give it a valve clearance check, as the valves may have pocketed, leading to tight clearances (or no clearance) Then check for air leaks, cracked pipes if it is injected, or leaks at the injectors or especially manifold gaskets, best way is with engine running spray carb cleaner at any possible leak sources, any change in running shows a leak. Worth checking all exhaust parts for blowing as any blows can cause popping on the overrun too. Obviously check timing and plugs.

Hmm might be totally different in my case but I have a Mk2 XR2 which pops on over-run. I know its not the exhaust manifold as its been replaced in the time ive had the car and it made no difference to the popping. I quite like it actually! The lumpy ride is vaguely apparent on my ride but I just feed it in with clutch and its fine. I dont even notice I do it anymore, just part of the way you get used to driving certain cars I guess

M

Hi Hawkey

Maybe a problem with distributor weights, I'm sure the dizzi's on these are supposed to give loads of ignition correction on over run for emission reasons, maybe they are stuck or the dizzi is worn or one of the numerous vacuum doohikies are blocked.

Hi,

Had a similar problem recently on my 1983 SIII Land Rover with 2.25 Petrol.

I found there was a combination of things that were causing the problems :

1) Vacuum pipes to distributor were leaking and at one point not even connected correctly. 2) Exhaust had come loose on the manifold. 3) Poor quality ignition leads.

Now runs fine.

Good luck.

Regards

Andy