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dieseling problem

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Daniel Kaminsky

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Dieseling on my BJ8 since we put in new electronic ignition. Same 91 octane non-ethanol gas, rebuilt tuned carbs before ignition install, supposedly properly adjusted timing.... What else could it be??
 
A few thoughts: Did the car diesel after rebuilding and tuning the carbs, but before the new ignition system was installed? Did you check the timing with a timing light? Could there be any vacuum/air leaks after rebuilding and installing the carbs? Are the float levels set correctly, and are the float valves in good condition? GL, Jim
 
Idle speed? The most common cause of dieseling--assuming timing, etc. is correct--in my experience is idle speed set over 750RPM.
 
No, did not diesel after carb rebuild. My man has supposedly checked the timing--with a light, I don't know. The rest i will run by him as I am not doing to work. Many thanks for you help.
 
I don't know why switching to an electronic ignition alone would cause running on but I would inspect and perhaps change the plugs to one grade colder. Also I think your car would benefit from better fuel.
 
First thing I'd do if it's not too difficult is to change the ignition back to what it was and if the dieseling stops you've isolated your problem. If it's ignition relate, I wonder if a hotter spark that's keeping the combustion chamber hotter and allowing the remaining fuel to ignite after shut off. Also possible there's some carbon buildup in the combustion chambers that stays glowing after shut down, causing the diesel. In order of what I'd do is check for raised idle speed, revert to regular ignition and try colder plugs.
 
Michael and Rick make interesting suggestions. I now remember a problem back in the '70s. A friend had a similar issue with his Spitfire. He had changed the plugs and other ignition parts, but had not checked that the plugs were the correct heat range- or at least the same type that he had been using. The car dieseled badly, and he chased the problem for a couple of weekends, unfortunately messing up almost everything that he could adjust. An "old guy" (probably about 31) that we knew figured out the new plugs were two steps hotter. Replacing them with the original parts solved the problem.

Were your plugs changed?

As to the electronic ignition, I assume (and that can be bad!) that by replacing the points with the pick-up hardware for the electronic ignition, the timing could have advanced (like adjusting the points affects the timing). That could cause the car to run on. Jim
 
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Any little thingie that lights up in the combustion chamber can cause running on--carbon deposits, sharp edges, crap on spark plugs from crummy gas, etc. Also improper ignition timing can be a cause, resulting in things lighting up at the wrong time in the ignition sequence, causing running on and other issues.

I see that you are "not doing your own work" and this is a great place to begin learning. Invest in a timing light and check it out yourself--even if you don't rectify the problem you'll have acquired new knowledge and feel that much more confident about owning your Healey. Get the kind with an digital advance--it is easier to use and can also verify your tach's reading.
 
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Then there is always this: let out the clutch and stall the engine after turning the ignition off.
 
Then there is always this: let out the clutch and stall the engine after turning the ignition off.
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That's the way I always do it. Mine runs on some times but not always and in almost all cases I want it in gear when I park, so I roll up to a stop, put it in 1st, turn key off, lift clutch.
It becomes habit and is no inconvenience at all (and no one knows you have a dieseling problem:smile:).
Dave
 
HealeyRick said:
If you buy your own timing light, make sure it is compatible with your electronic ignition. Some lights won't work with certain ignition electronics.
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Many newer lights seem to be poorly shielded, so the ignition noise from older cars may interfere with their measurement - in some cases a lot. The inductive pick-up can also be trouble. Personally, I would be wary of timing lights from Harbor Freight and other discount stores. You don't need to spend a fortune for a Snap On brand timing light, but a bit of research might save a lot of frustration.
 
May not be related to healeys but worth checking thermostat and general cooling & ventilation we often get run on in marine engines with the issue of poor air flow usually run engine at idle for a period before shut down cures the problem.
 
It is very comforting to see how frequently so many of us need to stall the engine after shutting it off. It’s not a problem...it’s a feature.
 
4tecdog said:
May not be related to healeys but worth checking thermostat and general cooling & ventilation we often get run on in marine engines with the issue of poor air flow usually run engine at idle for a period before shut down cures the problem.
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Thank you 4tecdog! Will try this out.
 
moremonkey said:
It is very comforting to see how frequently so many of us need to stall the engine after shutting it off. It’s not a problem...it’s a feature.
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I remember air-cooled VWs had an anti-dieseling solenoid on the carb which would shut off the flow of fuel from the float chamber when the ignition was turned off. Would that we had such a device on our HD-series carbs on the bottom between the float bowl and main jet.
 
steveg said:
I remember air-cooled VWs had an anti-dieseling solenoid on the carb which would shut off the flow of fuel from the float chamber when the ignition was turned off. Would that we had such a device on our HD-series carbs on the bottom between the float bowl and main jet.
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With Lucas electrics? Remember the 'automatic' enrichment circuits?
 
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