I am stumped on the mystery of my engine. Whenever I get the total timing at 36*, the engine is sluggish at times and backfires through the carb and diesels after I shut it off. When I advance it a little more, the backfiring goes away but still diesels. When I retard it, dieseling goes away but backfires more often. I feel like its either/or if I want to be able to drive it.

I have swapped a crate L31 with a Lunati 20080660 cam, a Holley Street Warrior with the default fuel mixture (1.5 screw turns from lightly seated), and a Electric 7psi Edelbrock fuel pump to get fuel to the carb. I am also using Autolite Iridium XP sparkplugs.

I appreciate the help and feel free to ask questions.

 

Whenever this scenario arises, it is usually a good idea to verify the timing marks with the actual mechanical TDC of the engine. A new crank, new balancer, new timing cover and tab, and other variables can result in the timing marks being WAY off actual piston TDC.

 

There's a lot that's capable to be to blame but just a random thought, is the fuel fresh?

 

Fresh 87 Octane.

 

What happens when you bump the octane up? What's compression?

 

I haven’t tried a different octane yet. I have a similar setup of a L31, but minus the cam, run 87 perfectly. It’s a 9.4:1 compression.

 

Did you have this engine running before the cam? Did you degree the cam to check and see if it is what it claims to be? Just tossing out ideas since the list of possibilities isn't exactly short. I wouldn't rely on the timing marks to confirm what degree its at, that's for sure. Verification of that will help, but the number itself isn't important if the engine is happy.

 

I never had it running before the cam. I bought the engine off Marketplace that had the cam pre installed. The guy I bought it from decided to go the LS route for his vehicle.

 

then I wouldn't trust the mechanicals in the least. Me personally, I'd take the whole thing apart.

 

I agree. Unless you hear it running before you buy it, I wouldn't trust anything inside.