Gotta think beyond the plug firing. The big thing on dieseling is hot engine and enough fuel to fire off the heat.
One way you get enough fuel is set the idle speed up (open the throttle plate) to keep the engine idling where you want it. Also perhaps mixture screw may be too open allowing a richer mixture.
If the timing is too slow, you have to open the throttle plates a little more to get the engine idle speed you want. If the plates are open enough, when the engine warms up, it may allow enough fuel to flow through to be able to fire the cylinder even though the ignition is off.
Also, when the timing is too slow, things tend to heat up quicker and more of the cylinder is exposed to the explosion caused on the compression stroke. The more cylinder that is hot, the easier it is for the engine to diesel when the switch is turned off.
Getting the timing where it should be allows the throttle plates to be closed a little more and less fuel / air enteriing the engine. Also, less cylinder is exposed to the heat during the explosion in the cylinder.
Some manufacturers added a solenopid to open the throttle plates a little when the switch was turned on and then when turnd off allowed the throttle plates to close more shutting off the air fuel mixture.
Does this help a little?
In this case he may simply have the idle speed too high and just bringing thst down may help.
Last edited by Roy Rodgers; 06/21/2011 11:08 PM.
