I have had nothing but trouble with my '38 Pick-up since returning from Bonneville. Here's the sitch.... Idles fine Revs fine Sounds fine But when I take off it keeps backfiring! If I stomp on it it doesn't do it though. I have changed the plugs,points,condensor,rotor,cap,vac advance,and the coil. The timing is right,dwell is right,idle is right...I just can't figure it out. It has a '59 Chevy 283 Fuelie motor,Edelbrock 600(man choke). I'm about ready to just drop it off at my friends shop,but I HATE PAYING SOMEONE TO FIX MY CARS!!!! ANY suggestions would be HIGHLY appreciated.
Look for an exhaust leak - having same problem with mine - when I left off gas air gets sucked in and ignites the rich fuel. Do a google search lots of info on it
I'm up for anything...It probably needs new exhaust gaskets anyways. Didn't sell it yet. Can't really push trying to sell it if it's acting up. I'll mess with it some more this weekend. Has new filter...
Sometimes, backfires indicate that you are running too lean. You say that you have an Edelbrock 600 / manual choke... I'm guessing that you are referring to a model 1405. Next time it backfires, pull the choke knob out slightly. If the backfires stop, it may be a "lean" issue. If thats the case, it could be just a slight adjustment, or maybe its time to look at your jets. ...robber
Bob your accerator pump is miss adjusted. Pull the air cleaner off and with the motor off move the throttle. If you can move the throttle any with out seeing a squirt of fuel then that is your problem. Lean . Just adjust it until any movement of the throttle gives you a squirt.
Check the points lead into the distributor. Had a bad one once that would misfire at light throttle when the vacuum advance was in just the right spot.
if its a small sneeze as you tip into the pedal off idle i would think its the lean condition as mentioned above. If you want to try a simple test add a 1/8 to 1/4 turn richer to your idle mixture and see if it changes it. and always make sure its at operating temp when making changes and evaluating success.
turn the truck off, look down carb, pull carb linkage and see if you are getting a good squirt of gas... Are you sure there is nothing funny going on with your ignition timing? Have you brought the engine to TDC in number 1, then check the harmonic balancer and pointer to make sure your timing mark is correct = have timing correct? when you set initial timing you have distributor disconnected, then connect it to metered vacumn at the carb? What is your initial advance, and what is your total advance with the vacumn advanced not hooked up, and total with vacumn advance hooked up?
I am not saying you are a fool but in Bob's post he says he has a Edelbrock 600. But what do I know.l
we have had a couple come thru the shop with those carbs that were doing the same thing. in those instances we took the carb off and douched it out (soaked it) pretty good, put it back together and it was smooth as silk. the slightest bit of crud in the off idle circuit can wreak all kinds of havoc. in my experience with these carbs, a weak acc. pump will cause a stumble/hesitation off idle. but i'd still check it.
Had an old mechanic teach me this when I was young.. " If it backfires out the ass, its in the gas... out the carb its the ignition or timing." works every time to help get a little closer to the problem.... Good luck.
So, Bob...you haven't said which end it's backfiring from..intake or exhaust. or both? I don't trust those cheapie Chinese distributor caps, myself. I've had bad luck with them. And double check your firing order. Some guys get a kick out of swapping #5 and 7 plug wires. 18436572 clockwise. And no, I didn't do it when we were at B'ville. Damn, now if that's the problem, you really will think I did it! Anyway, check it. A flat cam will backfire the most under heavy load and you said your engine runs fine under load..
I'm writing all these suggestions down so I can check them all off tomorrow. I'll let you know if anything solves the problem. Thanks....
since you run a point distributor-does it have an inline resistor block between switch and coil? check that out......have seen those fail.
Not yet mentioned... Check for spark plug wire arcing. Also I've seen weird behavior like this when dist bushings start to go, your dwell will look okay at first but it shouldn't vary or bounce with a rev.
Okay,,,here's the latest. I took off the carb. Gave it a thorough cleaning. Found that one of the metering rods was bent and stuck. Don't know if that's what made it backfire,but it definately isn't right. Put it back on and drove it around the block.....NO BACKFIRE,so far! I'm gonna drive it some more when I get off today and see how it does. I'm thinking of going with a 3-duece set-up and be done with the Edelbrock. JustplainJ has a buddy who refurbishes 94's. I'll let you guys know how it does this weekend.
Tried to drive it on Sunday....TRIED! Still not working. Think i'll put my Merc carb on it this weekend,to see if it makes any difference. Same carb,but brand new. If it still backfires,then I know it isn't the carb. SUCKS! Can't sell it if it isn't running...
I did not read every post cause I'm at work but I have experienced the same problem as you mentioned above. Found out it was just a bad tank of gas. My truck (62 Chevy 283) was running perfect...at idle, on the street and highway. So I leave to go to Bonneville and stop and get gas at a place that I never get gas at, hit the freeway and my truck is back firing like crazy. So I pull over and tweak the timing, put new plug wires...nothing. So I figured I will keep driving. Burnt thru the tank of gas and stopped at Shell in Oregon, got back on the freeway and no more back firing.Never had the problem again.
Bob, I had a similar problem @ bill 's shop . What carb are you running ? My problem was in the idle circuit.
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