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+--- Thread: Single misfire (/showthread.php?tid=8090)
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RE: Single misfire - Tod - 05-06-2023
I had a similar issue several years ago with my Ruby. I traced it to a faulty lift pump. It may be worth checking.
Tod
RE: Single misfire - Peter Naulls - 05-06-2023
Faulty in what way Tod? I did wonder if it was running short of fuel but haven't been able to catch it with anything less than a full carb.
RE: Single misfire - Tod - 06-06-2023
Peter, I found that the diaphragm had swollen, (in my opinion by the ethanol used in petrol). This greatly reduced the effective working stroke of the diaphragm, hence the fuel delivery quantity . The car ran as normal when under a light load, however long hills especially, were a problem. It took a while to actually figure out what was happening.
Tod
RE: Single misfire - Reckless Rat - 06-06-2023
The red coloured diaphragms sold by the Seven Workshop are E10 compliant.
RE: Single misfire - "Slack Alice" Simon - 06-06-2023
You don't mention it, I assume you have tried another set of plugs?
Is the distributor drive gear ok - some have a habit of wearing away to nothing. I can get mine to backfire by retarding the ignition, so timing can have a similar effect to an air leak.
Cracked cylinder head?
RE: Single misfire - Peter Naulls - 06-06-2023
Many thanks for all your suggestions, on and offline.
The pump does have a Seven Workshop diaphragm but I guess it could have developed a leak or valve problem. I'll check that next I think.
No I haven't changed the plugs. When it really fails it's not a distinct misfire, more a fluffing and hesitancy... and the stalling. However, I probably should change them just to rule them out.
Distributor drive gear is good, having destroyed a couple of chocolate replacements I now have a good original one back in there. Timing is fine too.
Cylinder head? I didn't think of that. Where do they crack typically? There's no water loss and the head gasket looked to be intact when I changed it.
RE: Single misfire - "Slack Alice" Simon - 06-06-2023
I don't think they do crack, typically. But your post nudged some obscure memory that someone, on here or in a club mag, had a cracked cylinder head.
Can't believe it would provoke "fluffy" behavious, just straw clutching.
RE: Single misfire - Adrian Payne - 06-06-2023
Hello Paul
Still sounds like a valve issue. Could it be a cracked cam follower where the cone nut has been done up too tight and now jams in the guide. These have been known to hold a valve open.
Adrian.
RE: Single misfire - Peter Naulls - 06-06-2023
Hi Adrian, Simon etc,
The followers were all checked whilst the valves were out so I think it is unlikely now. I am beginning to think the original "single misfire at speed" was a separate issue (possibly the gummed up valve stem causing it to stick) and that the current problem is due to weak mixture.
I need the car for work tomorrow but I'll check the pump valves and diaphragm at the weekend. If it's not that then it has been suggested that a worn butterfly spindle may be the cause. My spare carb is a bit of an unknown quantity but it may be a useful comparison.
I'll keep you all posted, your collective wisdom is much appreciated.