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Engine Dieseling a Bit at Shut Down

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Bobbee44

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The 1960 BT-7 with the auxiliary carb (read "automatic choke") is starting exceptionally well after a bit of tinkering, and a $5.00 retainer spring. The car diesels about 60% of the time at shutdown, not matter how long I let it idle after driving, rev it up to "clear things out," or just shut down after a drive. I have cleaned and properly gapped the plugs, used an additive in the gas to boost octane (I use 93 octane pump gas) and added a bit of "fake" lead. The car runs well and cool at all speeds and revs.

Nothing worse than driving up to someone and turning off the key to have the engine grunt, shake and weeze like it's about to give it up for good.

Any ideas?

Thanks,

Bob
 
Until you find out what's causing it , kill the engine by letting out the clutch and holding the brakes on right when you turn off the key. It won't hurt the engine or clutch. Its not good to let 'em diesel it will shake a bunch of stuff loose. Mine did the same thing before I rebuilt the engine. They get a lot of carbon buildup that keeps 'em running.
 
Nothing worse than driving up to someone and turning off the key to have the engine grunt, shake and weeze like it's about to give it up for good.

Yep,BOB;
And too much of that will make it give up for good..

Chek the plugs and make sure that you are not runing too rich and reduce the idle speed if possible. A high runing temperature can also contribute to this problem.
 
What's the idle speed? Anything much above 700rpm will contribute to dieseling.

If it won't idle nicely at 650 then a good carb tuneup will help. Worn throttle spindles are a pretty common cause of high idle. Andy.
 
I'm thinking along the lines of the engine running a little too lean, creating hotter combustion chamber temperatures.
 
If this is a high mileage engine and there are big carbon deposits on the pistons, the carbon will continue to glow after you have turned off the key......thereby, continuing the combustion process.
So, if this were my car, I would try a little trick I learned in the middle of the last century. Rev up the engine a bit and dribble some water into the carbs. The water will blast the carbon off of the pistons. Have a friend handy to watch the tailpipe while you do this. If there is a carbon buildup, your friend will see some stuff come flying out the tail pipe and can confirm to you that the trick worked. If you do it only by yourself, you may not see what, if anything, comes flying out of your tail pipe.
 
I would not spray water into my Healey engine, maybe drive it on a misty damp day with the bonnet cracked open, Ha...
 
Thanks to all who responded. I had not touched the HD-6 SU carbs. After a quick tutorial, I found the carbs were not blanced, one was running rich while one was running exceptionally lean. I have a smoothly ideling BT-7 that has not dieseled since...fingers crossed.

Cheers,

Bob
 
Well done Bob, always check the simple things first..
I remember that my car was a B"""""d to start in the mornings, after 8 years I got the timing checked and it was way out.
Starts first time now - or did before I stripped out the engine for a rebuild.

:cheers:

Bob
 
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