abe72 Posted June 22, 2011 Share Posted June 22, 2011 Hello everyone, I have a question and need help. I have a stock '72 350 2 barrel and as far as I know it pretty much has most of its original parts. My question/problem is, I get a backfire/pop when I rev up the engine in park or neutral. What can be causing this? Some have told me that it could be my smog/air pump others say it's the air fuel mixture/timing. I'm not a hard core mechanic unlike some of you (judging by the engine pics) on this bored and would appreciate any advise or help. Thanks Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted June 22, 2011 Share Posted June 22, 2011 How long since a tune up? How old are the wires and cap? Quote Link to comment Share on other sites More sharing options...
abe72 Posted June 22, 2011 Author Share Posted June 22, 2011 It's been about 10 months since a tune up. Cap,plugs, points and condenser were changed but the the wires. I'll be converting it to an electronic ignition soon. Quote Link to comment Share on other sites More sharing options...
stangeba Posted June 22, 2011 Share Posted June 22, 2011 When driving under a heavy load, like WOT, prior to the 1 2 shift, I assume it misses and runs poor? I also think it sounds like plug wires. When I checked my plug wires, because of a miss last spring with an OHM meter, 6 were bad and the coil wire was also bad yet it ran fine in the fall when I put it away for the winter. Bruce Quote Link to comment Share on other sites More sharing options...
abe72 Posted June 22, 2011 Author Share Posted June 22, 2011 Okay, I'll check the wires for now. New wires when it gets converted. It runs fine no problems or backfire, just when it revs up and decelerates. Quote Link to comment Share on other sites More sharing options...
Mo's70MCs Posted June 22, 2011 Share Posted June 22, 2011 Okay, I'll check the wires for now. New wires when it gets converted. It runs fine no problems or backfire, just when it revs up and decelerates. the early emission control in that year (72) car is prone to that. Specially Cal emission, I don't know if 49 states were the same. air injection reaction (exhaust emission control ) system " anti backfire valve" If I recall correctly it's mounted and bolted to the smog pump.. If you unplug its vacuum hose and it backfires less or non at all it's the valve... just when it revs up and decelerates. Maybe someone else will chime in and back-me up. Quote Link to comment Share on other sites More sharing options...
abe72 Posted June 23, 2011 Author Share Posted June 23, 2011 Okay, so I disconnected the two hoses that go from the pump to the manifoids and it dose not backfire when I decelerate. I'm gonna to asume that it the "anti backfire valve" is this also known as a "diverter valve"? Can this valve be repaired/fixed or once it gone bad... Would it damage the engine if the vacum hoses were to be pluged and the pump contniues to blow air,or should the pump be capped too? Quote Link to comment Share on other sites More sharing options...
Mo's70MCs Posted June 23, 2011 Share Posted June 23, 2011 "diverter valve"? Good question cause I have heard it called by that name , but not sure it relates to the same valve we speak of. I don't know if the valve can be serviced, and being that I own '70s my interest in emission control in a non-regulated car is "ZERO" . Most owners do away with emission control stuff..I'd get rid of the pump, plumbing, if it were mine. The state of Cal might not like it. I feel if it's registered, why not?.. take those pesky performance robbing trinkets and store them, and provide those items if you ever sell the car. Probably robbing your MPG as well. JMHO Quote Link to comment Share on other sites More sharing options...
CrazyDavey Posted June 23, 2011 Share Posted June 23, 2011 '76 and older....no smog check required....bag it...label it....put it on the shelf.....right next to the cans with dried up paint inside... Quote Link to comment Share on other sites More sharing options...
wallaby Posted June 23, 2011 Share Posted June 23, 2011 ...put it on the shelf.....right next to the cans with dried up paint inside... Quote Link to comment Share on other sites More sharing options...
abe72 Posted June 23, 2011 Author Share Posted June 23, 2011 Thank you all for your advise and suggestions. Most of the people I've spoken to about it pretty much have the same idea, "put it on the shelf" no longer required as mentioned. Quote Link to comment Share on other sites More sharing options...
abe72 Posted June 25, 2011 Author Share Posted June 25, 2011 Well, I think I figured out the backfire issue. I notice there was a vacuum line disconnected going to the pump (valve) then adjusted the carburetor (running rich) and changed the plugs. Running much better and no backfire. Thanks to everyone for the advise and suggestions. Quote Link to comment Share on other sites More sharing options...
Mo's70MCs Posted June 25, 2011 Share Posted June 25, 2011 good going! nothing like the satisfaction of finding the problem yourself. This forum offers a wealth of information.. just go ahead and ask. You'll find your answer here.. Quote Link to comment Share on other sites More sharing options...
CrazyDavey Posted June 25, 2011 Share Posted June 25, 2011 good going! nothing like the satisfaction of finding the problem yourself. This forum offers a wealth of information.. just go ahead and ask. You'll find your answer here.. this is true Rod except most of the time we have the poor devil rebuild the motor only to find a hose fell off.... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.