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2.25 Petrol Running Problems


jordan_meakin
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Having problems with my Series III with a 2.25 petrol.

At low revs and through hard acceleration, the engine is "spitting" or mis-firing. It has been off the road for quite some time as I have been doing various bits of work (including carb. rebuild). I have also replaced the ignition system to rule it out.

I have done a compression test and it's reading around 9 bar across all cylinders. However, I have noticed that if I remove the leads from cylinders one and two whilst running, it does not cut out. However, from 3 and 4, it does. Hence the compression test - head gasket? There are no symptoms of head-gasket failure. Oil is clean, water is clean, no clouds of steam etc.

Does anyone have any ideas? I am hoping I haven't done anything wrong on the carb... It runs quite well when on the road and revving harder just this annoying mis-fire that I would usually associate to dirty points, bad leads etc but, as I say - already ruled that out.

Any help greatly appreciated!

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It does sound like it's either running too lean or sucking air. It could be as simple as a vacuum connection not, um, connected on your manifold. Failing that, if the carb has been off and dry for some time, there could be a little corrosion in a jet.

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Could be a faulty coil getting hot, had this on my s111 years ago driving from Manchester to Cornwall towing a caravan lookerly my bro was with us in his s11a so we got to the services and found a local motorist shop and bought a new coil fitted it and everything was ok again, hope you get it sorted :)

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Hi all,

Thanks for the replies.

The problems occurred after it was laid up but has been off the road for a year hence suspecting ignition. As I've replaced all that again, I feel it rules it out...

I have replaced all gaskets and lapped the carb faces to seal air leaks (that's why I did it) and replaced all jets etc. in the process. It was basically a process of dismantling and replacing like for like, cleaning along the way. I must say, carbs make me nervous because I don't really understand them! Do you think running badly on only some of the cylinders would be a symptom of carb problems? Bloody Zeniths!!!

Appreciate any help as always.

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Hmm, re-reading your first post, you've actually pin-pointed the problem to cylinders one and two. Highly unlikely you've put the leads on wrong but....

Also check the distributor cap for a crack (it could be invisible but you may see a trace of carbon).

Another possibility is that some valves have got sticky. This was very common a few decades ago, if a vehicle sat for a bit. Whip the rocker cover off and check tappet settings but also tap each valve down with a soft hammer and see if it immediately bounces back. A sticky one is obvious because it makes a dull sound, not at all like the good valves. It would only take a slightly poor seat to give those symptoms.

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Do you think running badly on only some of the cylinders would be a symptom of carb problems? Bloody Zeniths!!!

I can't answer that definitively I'm afraid but I do know that after refurbing my S3 carb with new jets etc. I has a mis-fire which was caused by dirt that carb spray dissolved / removed.

To isolate the problem to the cylinders could you exchange the leads from dist to plugs one by one from a "good" cylinder to a "bad" and secondly try swapping plugs in the same way?

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  • 2 weeks later...

Good news and a good diagnosis Deep.

Also thank you for coming back with a conclusion - these really make the threads useful. So often when searching for something on an internet thread it just stops...

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I think it's that blind assumption that a new part is okay, a trap that I have fallen in before! I did a lot of work all at once and it never crossed my mind that the servo would be the culprit despite noticing a very loud sucking! What a fool I suppose...

Thanks all!

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Good news and a good diagnosis Deep.

Also thank you for coming back with a conclusion - these really make the threads useful. So often when searching for something on an internet thread it just stops...

Ta - and excellent point about coming back with the conclusion. It's the real way we learn here!

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