Backfiring, why?

[NAZ]

FF33rod, it's extremely difficult to troubleshoot even simple issues over the internet but a clear description of the symptoms will help. When you say "backfire" what does that mean to you? If I understand, seconds after starting you hear "pops" -- where is that coming from? Exhaust? Intake? Yes it makes a difference. If you hear and visually see evidence of backfiring out the throttle body (intake) the root cause is very different than if you hear a popping noise out the exhaust.

You're getting lots of ideas here but they are scattered all over the place. Try to be very specific in describing the symptoms. Or better yet, take it to a shop you trust -- you need help, and this is the most direct way to get it. You put the monkey on the back of the mechanic and he will follow a systematic troubleshooting approach to identifying the problem. Since this is a 302 based engine I'd recommend a Ford dealership. I've been troubleshooting engine problems for half a century and made my living at it as a Ford technician and I can't determine if you are really experiencing a backfire condition or a "popping" noise out the exhaust. Two totally different issues.

If it is backfiring (combustion in the intake tract) the two primary causes are timing too advanced or leaking intake valve. The fire starts in the combustion chamber and even on a very radical cam the intake closes 30-degrees before the spark is initiated at full advance. A backfire is caused by the combustion ether taking place before the intake valve closes (way advanced) or the valve is leaking igniting fuel in the intake. There is no other source of ignition in the intake tract.

If you haven't verified that your timing pointer is reading zero at actual TDC (requires a TDC finder) then you are simply guessing at your base timing and could actually be very different than what you believe it to be. Since this was a short block build with aftermarket heads you supplied that means you had to spec the correct length push rods and should have verified that the engine builder correctly timed the cam. And the hydraulic lifters have to be adjusted correctly. A grossly mis-adjusted lifter can hold open a valve. And since this is a roller, the cam requires a button to limit end play -- if end play is not correct your timing will wander as the cam end play will affect the distributor motion. Couple that with incorrect base timing and you may be way too advanced on the ignition lead. Erratic timing can be picked up with a timing light as your lead will move around during steady idle.

[FF33rod]

FF33rod, it's extremely difficult to troubleshoot even simple issues over the internet but a clear description of the symptoms will help. When you say "backfire" what does that mean to you? If I understand, seconds after starting you hear "pops" -- where is that coming from? Exhaust? Intake? Yes it makes a difference. If you hear and visually see evidence of backfiring out the throttle body (intake) the root cause is very different than if you hear a popping noise out the exhaust.

You're getting lots of ideas here but they are scattered all over the place. Try to be very specific in describing the symptoms. Or better yet, take it to a shop you trust -- you need help, and this is the most direct way to get it. You put the monkey on the back of the mechanic and he will follow a systematic troubleshooting approach to identifying the problem. Since this is a 302 based engine I'd recommend a Ford dealership. I've been troubleshooting engine problems for half a century and made my living at it as a Ford technician and I can't determine if you are really experiencing a backfire condition or a "popping" noise out the exhaust. Two totally different issues.

If it is backfiring (combustion in the intake tract) the two primary causes are timing too advanced or leaking intake valve. The fire starts in the combustion chamber and even on a very radical cam the intake closes 30-degrees before the spark is initiated at full advance. A backfire is caused by the combustion ether taking place before the intake valve closes (way advanced) or the valve is leaking igniting fuel in the intake. There is no other source of ignition in the intake tract.

If you haven't verified that your timing pointer is reading zero at actual TDC (requires a TDC finder) then you are simply guessing at your base timing and could actually be very different than what you believe it to be. Since this was a short block build with aftermarket heads you supplied that means you had to spec the correct length push rods and should have verified that the engine builder correctly timed the cam. And the hydraulic lifters have to be adjusted correctly. A grossly mis-adjusted lifter can hold open a valve. And since this is a roller, the cam requires a button to limit end play -- if end play is not correct your timing will wander as the cam end play will affect the distributor motion. Couple that with incorrect base timing and you may be way too advanced on the ignition lead. Erratic timing can be picked up with a timing light as your lead will move around during steady idle.

NAZ, totally understood. I was already thinking along the lines of one of your key points - how does anyone really know what I'm referring to? I was thinking that a video or sound recording would help.

As for going to a Ford dealership, I'm pretty sure that I would be either stared at rather dumbfounded or be laughed at. That's not a knock on Ford but a statement on most dealership "mechanics" these days. With your experience and the era that you got your training, you're a true mechanic. Most these days need a place to plug in a computer and then they follow the instructions on the computer whether it makes sense or not. I could tell you some stories about BMW but you probably have similar ones of your own. Best idea I think would be to get an independent mechanic shop to look at it. However, I'm hoping it won't come to that.

As for all the parts playing together, except for the Holley Sniper and the "dress up" bits, I made it pretty simple by using a top end kit on top of a short block, both from TRE. So all pieces were known to perform well together and would fit. Yes, I properly adjusted hydraulic lifters, etc. So hopefully, I won't be discovering any issues in these areas.

Thanks again, I will be looking at the 180 possibility tonight and you'll be darn sure I'll report back.

Cheers, Steve

[HVACMAN]

I'm glad it turned out to be a simple fix. Maybe the port for the power brake booster?? It reminds me of a saying my Dad had and it has proven to be true. "It takes 15% of your time to fix 85% of your problems and the other 85% of your time to fix that last 15%