Gas engine "dieseling" and back/after fire
 

Just because my BBC is doing such only when warmed up to temp ~190 degrees, what are the causes of such events and possible fixes. I do intend to rebuild the engine, but I'm just wondering.

Re: Gas engine "dieseling" and back/after fire
 

Carbon build up is usually a big reason.

Re: Gas engine "dieseling" and back/after fire
 

x2 put on new head gasket recently and cleaned out what looked like small raisins of carbon on two cylinders. no problem with dieseling since

Re: Gas engine "dieseling" and back/after fire
 

Carbon, again, is often guilty. I've also had this problem before when my coil and/or coil wire (if you don't have coil in cap) is going south.

Re: Gas engine "dieseling" and back/after fire
 

idle to high, vacuum leak, timing off.

Re: Gas engine "dieseling" and back/after fire
 

To low octane gas or idle set to high. that's why carbon cleaning can help upped the compression to point you need hi test or premium these days . I would try higher grade gas or different station.

Re: Gas engine "dieseling" and back/after fire
 

Well after doing some work on it today I found the dizzy cap needed replaced and the advance was on ported vacuum so I switched to manifold vacuum and the high idle was set way to high. I guess I just need to learn how to tune a carb properly. Runs better and has more power. So this spring / summer I will just do head gaskets and put a dual plane intake on and run it till it needs rebuilt or I decide it's time

Re: Gas engine "dieseling" and back/after fire
 

Isn't dizzy advance supposed to be ported? Thats how my vac diagram shows it.

A worn out carb can do the backfire/after fire too. Mine did it forever till I replaced it.

Re: Gas engine "dieseling" and back/after fire
 

Yes dizzies are supposed to be ported but I do need to replace mine and putting it on manifold advances it sooner. My carb is a fresh rebuild edelbrock that I haven't really messed with alot, I bought it and installed it and then I got my blazer and really haven't drove the BB. The truck dieseled badly with the quadrajet on it. I do plan on rebuilding the q-jet when I do the head gaskets and put a new intake on, I found a dual plane spread/square bore for $250 so I can run either or, I just need to find an electric choke for the q-jet and I will be good to go.

Re: Gas engine "dieseling" and back/after fire
 

About the vacuum advance, have a read of this:
http://www.bangshift.com/forum/forum...vacuum-advance

Re: Gas engine "dieseling" and back/after fire
 

I stand, well sit, corrected. Thanks for the information Greg. You learn something new everyday.

Re: Gas engine "dieseling" and back/after fire
 

That was a fascinating read.