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By Canadian Hot Rodder - 18 Years Ago
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Hey Guys, Just a dumb question, my 56 has always popped or given a small backfire out of the exhaust when I decelerate or gear down from hard acceleration, but now it seems to be doing it everytime I let off the gas? The question is, is this a timing issue or a carb / fuel issue? The car is running fine, idles fine and has no problem accelerating? I'm woundering if my distributor moved a bit or if the problem lies in the holley carb? It is a little tough to set my timming as my damper has spun AGAIN  so I just set it by ear.Any thoughts, it is somewhat embarassing to hear my car banging away when I slow down!  Rob
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By Pete 55Tbird - 18 Years Ago
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In order to backfire in the exhaust you must have unburned fuel either from a too rich mixture or a misfiring spark plug. AT idle if you check your exhaust is it very rich(smells like gas)? I don`t think it is a spark timing issue. Pete
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By pintoplumber - 18 Years Ago
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Rob, I had an intake to head leak that was causing popping in the pipes for me.
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By MoonShadow - 18 Years Ago
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First check for a loose connection on the exhaust pipes at the manifold. Chuck
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By pegleg - 18 Years Ago
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Rob, Send Feistritzer a pm and see if he's got a damper, or Get hold of the Damper Doc and have it fixed. Ear's OK for the street, but not EXPO. Frank
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By pintoplumber - 18 Years Ago
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Frank, Lon won't be there, it's ok if he runs a little slower.
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By DANIEL TINDER - 18 Years Ago
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Rob,
When was the last time you set the timing by ear? As the points wear, the timing retards (the distributor doesn't have to move).
Try advancing until it just pings, and see if the popping goes away.
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By Moz - 18 Years Ago
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rob a funny thing happened to my 272 coming home from work it started popping out the tail pipe had a listen to it this morning & it sounded like a leaking valve i knew ir wasnt so i checked the carby & found the power valve was loose in the holley it was like it was open all the time i tightend it up & it runs fine no more popping check yours isnt loose or stuck open as this will give it to much fuel during decceleration when its normally closed. moz.
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By marvsmerc - 18 Years Ago
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Rob, I have the same problem on my Merc but haven't addressed it yet. Mine is the same-runs fine- and backfires when I let off. It is great though when I have Harleys behind me!!!I installed a good ole hand choke and I had left it out a little one day and the car didn't backfire so I figured I need to check my carb. I assumed It a fuel/air mixture problem.. Let me know if you correct yours and what you found. Mike
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By LON - 18 Years Ago
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Hey Rob , My offer still stands to do a real fine " Aussie " tune-up on your motor ???? I may not be at Columbus this year in person ,but I will be there in "Spirit ".Now let me see ,valve lash,.005 ,close points to .003,retard timing to 46 degrees ,etc,etc,??? Only kidding,mate . Good luck to you & whoever you race .My money is on "whoever " Regards Lon
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By Canadian Hot Rodder - 18 Years Ago
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Thanks for the suggestions guys, I've been too busy to even touch the car but Will let you know. I think I might be on the right track with the power valve though, it has stuck before and my RPM went way up. It also seems to be running a tad rich. Just have to find a day to test and tune. I have a spare carb that I have been meaning to rebuild, maybe this will get my butt in gear. Frank, I will email John and/or I been thinking og getting a new damper, getting things shipped up here is just a pian in the butt. Lon, it's about time I hear from you, I was starting to think I hurt your pride so much that you were too bashful to post on the site anymore!! Rob
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By pegleg - 18 Years Ago
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Rob, send it to me and we'll put it on the car at EXPO.
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By Canadian Hot Rodder - 18 Years Ago
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Frank,Send you the spare carb?
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By pegleg - 18 Years Ago
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Rob, You can, I'll get a kit here and do it up. I was talking about the damper, get one done and have him send it(them) to me or John, we'll bring it to EXPO and you can import it back to Maple Leaf Country in your toolbox.
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By Canadian Hot Rodder - 18 Years Ago
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Sorry I missunder stood Frank. Ive got a kit for the carb, and if I get a spare couple of nights I will build it. As for the damper, is the one off a truck motor the same as the passanger car? if so, I have a damper on a truck motor that I bought complete. Truck was a 56 1 ton, but I don't think it was the original motor. If there is a difference, how can I tell? Rob
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By Hoosier Hurricane - 18 Years Ago
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Rob: A lot of the big truck dampers had 1 narrow groove, 3/8 or 1/2 inch, and one about 5/8 wide for the fan belt. The fan mounted on a bracket above the timing cover instead of on the water pump shaft. I believe the water pump pulleys on those were cast iron and pressed directly on the water pump shaft. If the truck pulley looks like yours, it will probably fit. Only difference may be belt width, yours is probably 1/2", after '57 they were 3/8". As for your popping exhaust, as Pegleg said, check for an exhaust leak ahead of the mufflers. On deceleration, air will be drawn in through the leak, allowing any unburned fuel to ignite in the pipe. John
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By pegleg - 18 Years Ago
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Rob, I have a pass car unit here in In. that's fallen apart. I can send it to damper Doc, but you have to pay for it!! in US Coin rob. John m,ight have one that's still together, might be cheaper. Frank
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By Canadian Hot Rodder - 18 Years Ago
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I appreciate the help guys, let me check this truck damper out first and I will let you know. As for the popping, I agree with John on the exhaust leak, for I did have a crack in my drivers side header. Thats all fixed now. I still think it's the carb though for it is not consitent. I had the car out to a cruise night yesterday, no popping on the way there, but it was popping on the way home?  Still have not had time to rebuild the second carb, I will check for leaks and eventually bolt on the rebuilt carb and see what happens. Until then I will just keep scaring the poor scrub that's behind me!  Rob
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By Y block Billy - 18 Years Ago
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Rob, My Car has done that a couple times, One time I know was water in the gas, my car was running beautiful and filled up the tank and it started popping shortly after until I ran that tank down and freshened it up with some dry gas. The other time I played with carb and timing and got rid of it. I am now running a 4100 so there should not be any more issues.
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