John Spaur asked: I'll try not to run on about this one but my Healey does a bit... run on after switching off. Recently put it on the road and remember that dieseling can be caused by timming. I run 92 octane gas, recently set the valves [hot], timming, and carbs to what should be factory specs. What might cause some, but not excessive, dieseling? What might I try to solve the situation or is some dieseling normal? Thanks in advance for your help and to all those that have helped in the past!
From: Olin Kane
Your dieseling may be the result of excessive carbon deposits on top of the pistons (that continue to glow a little while after shut down). This would result if your mixture was too rich. This can easily be verified by checking your plugs after letting the engine get hot and running it at speed for 15-30 minutes. Check all plugs to insure that they are not soot coated but rather tan or grey.
From: Larry Heffner
Another Healey owner in our club recently had the same problem with his '61 and it turned out the dieseling was caused by the car running too rich. Someone had tried to set the idle using the the "Throttle stop lever screw" instead of the "slow-run valve" as the Brits call them in the manual I have.
If you are standing on the driver's side of the car, facing the carburetors, the "slow-run valve" (idle screw) is the large one to the right rear of each carb. The Idle Screw should be screwed closed and then backed off about 3 turns. If my memory is correct, the "Throttle stop lever screw" (which controls the air/fuel mixture) should be adjusted so a piece of newspaper slides easily under it. Also, I just found out that all adjustments should be made with the air cleaners and vacuum lines installed. Other folks on the net may have a better description than this. Sure is easier to adjust than to describe in words. Good Luck.
From: Alan Seigrist
Hate to tell you, but AH's were built for the time when you could get high test gasoline (i.e. 96-100 octane). You can't anymore, so it's best to use an octane boost. The only other way to fix it is rebuild the engine with low-compression pistons ($$$!!).
Probably the single best octane boost available is Bardahl's Instead 'O Lead Gold. It comes in a black bottle and is sold at Grand Auto on the west coast (but should be available nationwide). In addition to the octane boost, it has a lead substitute, also useful since most gas in the US has very little lead anymore (there's also Bardhal's red bottle which works, but it doesn't have the lead substitute).
It's cheap, and you only need to use a half a bottle to treat a tankful (it will stop the dieseling guaranteed). It runs about $2.50 a bottle, so half a bottle only adds about a $1.00 to tank of gas (you still have to use 92 octane though).
Be careful of other octane boosts, because many of them are scams (think about it, octane boost makes no difference in most modern cars because all of them are designed to run on 88 octane, so why sell something that works... it doesn't matter to most of the driving public). One of the octane boosts that DOESN'T work is Octane 108. 104 works, but it is really expensive.
On last thing, if you don't have the boost in the tank, just turn off the engine with your foot on the clutch (in first gear), and then drop the clutch. That'll stop the deiseling as well!!! Hope that helps,
From: Allen Edwards
Always shut the engine off with the car in gear and the clutch dispressed. When it diesels, let the clutch out. That will stop it. Someone once told me, when hearing my Heealey diesel, "There will always be an England" as if to say that you just can't kill something British even by hitting the kill switch. Another thing you might try is a good run on the freeway at 125mph to burn off all the carbon deposits. I understand that it is these deposits that get so hot that they continue to ignite the mixture after the spark plugs are no longer doing the job.
From: John Sims
I've been working on cars on and off for 43 years (my first was when I was 14 rebuilding a 49 Ford before I could legally drive - but - California in the 50's was as close to Valhalla as anyone should ever dream to get) Anyway, we always corrected that problem by getting on a long stretch of road and blowing out the engine at high speed. Buildups were caused by a lot of city driving and a good long run on a freeway could cure many ills.
From: Gary Anderson, Editor, British Car Magazine
As with many other things Healey, there is a "righter" way to stop the car on the clutch -- as taught to me for concours shows when my high-compression 100M engine wouldn't stop as soon as the judges thought it ought.
Push in the clutch and the brake. Put the car in second or third gear. Let the clutch out s l o w l y just until the revs start to drop, then shut it off. Guaranteed it will shut down quietly and smoothly with no judders or lurches.