4879tool Posted June 3 Share Posted June 3 Hello everyone my names John and I'm excited to be a new member here. I'm having backfiring issues with my 83' F250 and was hoping you guys could help point me in the right direction to fix it because I'm at my wits end. To give you some background information, I recently replaced the carburetor, intake manifold, and eliminated all of the emissions junk that was on it. The new carburetor is an Edelbrock performer 750 and the new intake is a Weiand Stealth . I forgot to mention it's the 460 7.5l engine. It will idle just fine but when I go to drive it, it backfires when I accelerate and when I lay off the gas pedal. Pretty much the only time it doesn't backfire while driving is when I'm coasting. I've advanced the timing to 12 degrees which helped with the lag while accelerating but hasn't helped with the backfiring. At this point I'm not sure what to do and figured I'd swallow my pride and ask for help lol. Thank you in advance for any advice! Link to comment Share on other sites More sharing options...
viven44 Posted June 3 Share Posted June 3 Hey there welcome!! When you say backfire, do you mean "exhaust popping" ? If so, you are running too rich (or at least an imbalance). I went through something similar recently. A few questions. 1) What is your idle vacuum reading ? Any vacuum leaks around the intake and carburetor ? Carb should have a PCV port in the back and front. The unused one is plugged ? 2) Have you compression tested all cylinders ? Highly recommend starting there to rule out possibility of dead cylinders. 3) Are the plugs new ? If not are the plugs fouled possibly ? Link to comment Share on other sites More sharing options...
85lebaront2 Posted June 3 Share Posted June 3 Do you still have the air pump on the engine? That system can cause popping in the exhaust, and mine even shot a 2 foot flame out of the tailpipe one time. Link to comment Share on other sites More sharing options...
4879tool Posted June 4 Author Share Posted June 4 Hey there welcome!! When you say backfire, do you mean "exhaust popping" ? If so, you are running too rich (or at least an imbalance). I went through something similar recently. A few questions. 1) What is your idle vacuum reading ? Any vacuum leaks around the intake and carburetor ? Carb should have a PCV port in the back and front. The unused one is plugged ? 2) Have you compression tested all cylinders ? Highly recommend starting there to rule out possibility of dead cylinders. 3) Are the plugs new ? If not are the plugs fouled possibly ? Yes, I guess the better term for it would be "exhaust popping " rather than backfiring. To answer your questions, I haven't checked the idle vacuum to see what it reads, my knowledge on carburetors is limited at best so I will check and get back to you on that one. No leaks around the carb or intake. The PCV valve is plugged in the back and so is the unused one up front. I have not compression tested the cylinders yet, I'll have to stop by my local oriellys tomorrow and pick one up. The plugs and wires are all new and so is the cap to the distributor. Thank you Sir for responding, I appreciate the help! Link to comment Share on other sites More sharing options...
4879tool Posted June 4 Author Share Posted June 4 Do you still have the air pump on the engine? That system can cause popping in the exhaust, and mine even shot a 2 foot flame out of the tailpipe one time. The air pump is gone. Link to comment Share on other sites More sharing options...
viven44 Posted June 4 Share Posted June 4 Do you still have the air pump on the engine? That system can cause popping in the exhaust, and mine even shot a 2 foot flame out of the tailpipe one time. I am still running the "smog" pump on Big Blue 2WD. I swear the exhaust is like a blow torch!! If I get rid of it, will I increase my mpg since parasitic drag on the belt drive is reduced ?? I'm getting a healthy 8MPG at the moment I'm reluctant to get rid of it because besides the exhaust being hot, its fine otherwise. Also, the "tubes" that go to the back of the head will exist, I suppose them being there isn't an issue if the pump was removed. Link to comment Share on other sites More sharing options...
4879tool Posted June 4 Author Share Posted June 4 I am still running the "smog" pump on Big Blue 2WD. I swear the exhaust is like a blow torch!! If I get rid of it, will I increase my mpg since parasitic drag on the belt drive is reduced ?? I'm getting a healthy 8MPG at the moment I'm reluctant to get rid of it because besides the exhaust being hot, its fine otherwise. Also, the "tubes" that go to the back of the head will exist, I suppose them being there isn't an issue if the pump was removed. When I bought the truck back in December, the guy who I bought it from had bypassed the air pump by using a different belt. I got rid of mine when I was replacing the water pump because it kept getting in the way. Of course now I'm second guessing that decision because the truck wasn't " popping " before I removed all that emissions crap. Link to comment Share on other sites More sharing options...
viven44 Posted June 4 Share Posted June 4 When I bought the truck back in December, the guy who I bought it from had bypassed the air pump by using a different belt. I got rid of mine when I was replacing the water pump because it kept getting in the way. Of course now I'm second guessing that decision because the truck wasn't " popping " before I removed all that emissions crap. I got rid of all emissions on another 460 recently (except PCV)... that alone should not be causing your problems.. so don't fret that decision. You should be running a PCV valve though.. without that you won't regulated crankcase pressure well. When you say the PCV valve is plugged, is it the actual valve or the port on the carburetor ? The PCV valve is probably not related to the issue at hand but just curious. Link to comment Share on other sites More sharing options...
4879tool Posted June 4 Author Share Posted June 4 I got rid of all emissions on another 460 recently (except PCV)... that alone should not be causing your problems.. so don't fret that decision. You should be running a PCV valve though.. without that you won't regulated crankcase pressure well. When you say the PCV valve is plugged, is it the actual valve or the port on the carburetor ? The PCV valve is probably not related to the issue at hand but just curious. So on those Performer carbs they have a PCV port in the front of the carb in between the 2 vacuum ports if that makes sense. That's where I have my PCV running. Now there is also a port in the back of the carb which I didn't need so I plugged it with the threaded plug that came with the carb Link to comment Share on other sites More sharing options...
viven44 Posted June 4 Share Posted June 4 So on those Performer carbs they have a PCV port in the front of the carb in between the 2 vacuum ports if that makes sense. That's where I have my PCV running. Now there is also a port in the back of the carb which I didn't need so I plugged it with the threaded plug that came with the carb20240601_185446.jpg Ok you are good then 👍 Link to comment Share on other sites More sharing options...
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