engine dieseling after shutdown

[babyblu63]

hey all. I have the 292 engine. It will start to diesel when i turn the key off. is this because of a timing issue? I just got this truck 2 weeks ago and its already converted to the pointless ignition system. any ideas or tips would be helpful thanks

nick

[MXmaniac]

I had the same problem and started this thread a long time ago:

http://67-72chevytrucks.com/vboard/s...d.php?t=290095

There are some good suggestions in there. I put a different carburetor on and a GM HEI set-up out of a later model. I did both of these at the same time so I'm not sure which one made the difference. Good luck!

[Northern lights]

Could be as simple as the idle speed set too high.....or too much timeing.

[BMSJaX]

Could be a few different things;
1. Possible timing- try retarding
2. Engine heat- I had this problem used a cooler thermostat
3. Idle too high- also have had this problem
4. Idle mixture- probably too lean(causing heat)
5. Spark plugs wrong heat range
6. Carbon deposits on the cyl. head

Hope this helps steer you to a fix

[Eagar1]

It deisels because your throttle plates are not closed when you let off the throttle and it is drawing fuel.
Your throttle plates are open because you have other problems that force you to run your idle screw in too far to keep it running.
Do this...

Start with the carb, turn your idle mix scews all the way in until they bottom out gently. then turn them out 1 and 1/2 turns.
Back your idle speed screw off until it no longer contacts the linkage.
check to see if the plates are fully closed, if not see what is holding them open, could be the choke linkage.
Once that is done, put your engine on top dead center, dont go by the mark on your balancer, use a tool or make one (old plug with like a brass bolt threaded thru it) that goes into the #1 plug hole so the piston bottoms out on it and check your valve openings to make sure it is just before intake stroke, use a piece of cardboard or tape on the balancer covering the slash marks, rotate the engine each direction and place a mark where the ign needle points, remove the tool, then place a mark on tape in the center of the two marks, that is your true 0 timing. Compare that to what your balancer says.
You should be able to research how much total advance your engine should have, depending on cam, and carb combo, but I would say somewhere between 20 to 30 degrees total advance. disconnect the vacuum advance, and plug the port on the carb. Use your timing light and start the engine and run it to about 2500 to 3000 rpm and it should be at total advance. If its not between 20 to 30 degrees, advance the distributor so that it is. You will tell where it seems to run best. Clamp that down, then hook the vacuum advance back up, see if the engine will idle. If not check that your vacuum advance is working. At this point you will want to hook up a vacumm gauge. Make sure you have full manifold vacuum and not ported vacuum off the carb. If the engine wont idle, try backing the Idle mix screws out 1/4 to 1/2 turn at a time until it does, and check for your best vacuum reading, should be 15 to 20lbs. If you get to more than 3 or 4 full turns and it won't idle, screw them back in and go back to the 1 and 1/2 point. Here is where it gets dicey, because it should idle. You may try turning the idle speed screw up a little bit, but the more you turn it the more likely it will deisel. You may have blocked idle circuit, or leaking fuel internally or both.
Some carbs have a built in check valve or ball, or solenoid that blocks the fuel when no vacuum or no ignition is present, you may have to check that as well.
Other possibilties are carbon build up in the cylinders, plug heat range to hot, or running way to rich jetting so there is lots of fuel in the intake when you shut it down.