Engine dieseling

[Uriel]

I got my truck running nice now. Carb, hei ignition, true dials with no cats. Recently it started dieseling occasionally. Guy at the parts store says that in the winter we start getting ****** regular gas. That got me thinking, I've been filling with 87 octane, but tuned it with 93 in the tank. It was running perfectly, idle mixture and all that with 93. would using the ****** 87 possibly be causing it to run not quite right?

 

[Jims86]

Not really.
reset your timing with the engine warmed up, dist unpluged, and vac line blocked, in gear...maybe set it at 6*.
then go for an in gear idle of 550 rpm, using the throttle stop screw, then re tune the idle mixture screws...they usually end up being 2 1/4 turn out from bottomed out. run them out enough for the idle speed to drop a little, then back them off 1/8 to 1/4 turn. Check for Vac leaks just for the heck of it. How high you set your timing, and compression ratio will pretty much determin what grade of fuel you use.

 

[Uriel]

Checking for vacuum leaks should be easy. I have one vacuum line going from the carb to the dizzy, and 1 going to the brake booster. I'm pretty sure that's a vacuum line. i'll have to try that this weekend.

 

[Jims86]

Checking for vacuum leaks should be easy. I have one vacuum line going from the carb to the dizzy, and 1 going to the brake booster. I'm pretty sure that's a vacuum line. i'll have to try that this weekend.

also, you can plug your breather holes, and either attach a vacuum gauge to the dip stick tube, or run some propane from a torch down into the crank case to check the under side of the intake gaskets. You should see no vacuum.