I'm just talking "in theory" there... It's up to the person doing the diagnosis to ensure that his belief that the timing is at 15... really is at 15, and to use some common sense when it comes to checking things out.

I have seen the inside of engines that were so grunged that they would diesel anytime the engine had run longer than about 10 min. They also had very poor compression, and the timing was where it should be, as well as the carb not being rich. At that point, you begin to realize that some things really do require invasive repair.

I've never seen mildly advanced ignition timing result in dieseling, for instance. I've never seen advanced timing result in excessive heat in the cylinder. Only the opposite. Since we're dealing with an engine and other technologies derived in the 50's, we need to look back at mechanics OF the 50's and 60's and 70's, and see what others did to deal with it. Lots of cars had solenoids that closed the throttle when you turned the key off to stop dieseling. Lots of products were developed or applied to clean out combustion chambers to stop it... Among them were Marvel Mystery Oil and Berryman B12.

Then there was my dad's favorite... give it a tune up, put B12 in the tank (high concentration), run chemtool down the intake till it killed it, let it sit overnight, and then drive the crap out of it. Generally, it fogged out crap out the tailpipe so bad the first few hard runs that it looked like it was on fire, but it would clean up and by the time he got back, he could drive it in the driveway, lift the hood, crank the idle down a round or two to get to normal, and turn the key off and it would... stop normally. I've seen him take that approach for 3 days. Doing it twice a day... But he usually had good success. (my dad was an old school mechanic during the 60's and 70's) Of course Dad knew his customers and if it was a car belonging to someone who had never used more than the first 1/4 of the throttle, this was standard procedure. In some cases, Dad just had them put the B12 in the tank, drive it a day or two, and then bring it to him. In which case, when they were gone, he'd rod the daylights out of it and then return it to them with a charge for "overall evaluation" charge of a few bucks. And he'd make sure every vital bit was in good shape, too. They often knew what he did, but just were unwilling to do it themselves.

Now, stray voltage can make it run after you turn the key off and I've seen it before, but it always continued to just run, not sit and go knock, clank, bang, chug, as it randomly ignites in the cylinder just about as the motor dies, and the smell coming out the exhaust is all but lethal, and the engine lurches wildly about shaking the vehicle and sounding like it's coming apart.

Like I said, real diagnostics involves knowing what causes things, how they manifest themselves, and applying some rational cures.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

The old-time cure I used in my shop was to trickle water down the carb while running the engine at about 3000 rpm. I would use about a cup or two. The steam produced would break up the carbon deposits.

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Chuck Rivers, Webmaster

I did that with an old 318... in fact, i used the hose and did it for about 20 min. It made some small difference, but the engine was mostly beyond help

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.