The Stovebolt Site Forums The Shop Area Engine Shop Dieseling 261....

After a long run at 2000rpm
(32-35 mph) my engine keeps trying to run after the ignition is turned off. This is a military truck with 6.5 rear axle...top speed around 45 mph.

261 engine is rebuilt stock...less than 500 miles on the clock. Using NOS R44 sparkplugs fired with Pertronix.
Temp. stays at 170 degree with a 165 thermostat.

Is it indicative that it needs tweaking on the ignition timing? Advance or retard??

Thanks for your help.

Bob C.

Is it trying to run normally or is it loping along like it's trying to die but just won't? Both could be called "keeps running after the ignition is turned off" but would be completely different issues. FWIW this is discussed fairly regularly. Clink the "Search" link just above the text box and search for dieseling. You'll find lots to read.

Hy RAC1812, most of the time dieseling can be traced to a throttle that is open too much. Combustion cannot take place without oxygen and a properly closed throttle will not allow enough oxygen to support combustion. Hot spots in the combustion chamber may be ignition points, but without oxygen combustion cannot take place. The o.e.m.s installed solenoids on the throttle linkages in the seventies so that the throttles would close completely when the ignition was turned off. The vehicles curb idle was set using the solenoid which dropped back when the ignition was turned off. So I think you will have to adjust your throttle linkage to close more, get the engine idle r.p.m.down where it belongs, hope that helps.

Ditto on the idle speed. That's a pretty common problem on engines with a radical cam profile that won't let the engine idle at a normal speed. If you can tinker with the mixture and throttle stop screws to get a smooth idle at around 700 RPM or less (500 is better) your dieseling problem will probably disappear.
Jerry

Thanks guys.

I did adjust the idling speed a bit faster a few weeks ago and now thinking back it did not diesel before......

Also the possibility that the manual throttle cable is adjusted to tight and causes throttle plate from not closing properly.

will try those solutions first and let you know what happens.

I am running a rebuilt YF carb recommended by the forum's Carb King.

Keep in mind, referring to your original post, that ignition timing means nothing when true dieseling is occurring. With the key off the plugs aren't firing. You likely have one or more hot spots of some kind that are acting like glow plugs.

Do you happen to have an alternator installed instead of the OEM generator? It's possible to get a feedback from the alternator to the ignition circuit that can keep the ignition powered up with the switch off. Not likely, but it's worth checking for stray voltage at the coil during the run-on situation.
Jerry

Dieseling will make some clattering sounds as the engine struggles to continue running. A big difference in the way it sounds if the ignition system is still working due to alternator feedback. If you turn the ignition switch off and the engine clatters and runs terribly, then it most likely is dieseling. If you turn the ignition switch off and there is no drastic difference in the way the engine is running, then check for something feeding power to the coil even though the switch is off.

Ignition timing can contribute to this. If it is a bit too slow, sometimes the idle speed is adjusted to correct for slow idle, opening the throttle too far.

Bumping the timing up where it should be will tend to speed the idle up a little, and then you can idle it down to the correct speed.

So do some basic checks on the ignition timing, point gap and make sure is truly is "dieseling" rather that just running on due to ignition being fed power.

Problem seems to be solved.

Yes I have coverted to a 12SI with a diode for feed back/ It was really dieseling.....rattling..shaking then dies out.

Turned down idling to 600rpm from a fast 750...... re-adjusted the manual throttle cable to have just a smiggen of loose when fully closed.

Only had one fast run to the Hot Dog stand for lunch but it turned off cleanly.

Thanks for your insight...... as the engine is in a very tight COE cab it is easier to work from the top to reach the carb than to fish for the dizzy through a small access panel.

Having other minor issues since it has only been on the road since late June although I have been driving the rolling chassis on my property for a few years.

Last question....... for clutch issues am I better on the driveline forum or here????

Bob C

Driveline.