I'm running a new 500CFM Edelbrock 4 BBL on my Y block (292). It is a 55 engine with a later 57 distributor. When I run the vacuum advance to the small vacuum port on the left, it pops and sputters when I downshift or back off the gas (sounds like a drive-by shooting). When I hook the vac advance up to the small port on the right, it seems to run fine, but I remember being told that that was supposed to be for manifold vacuum, and the one on the left was timed port. What is causing this popping noise, too much advance. It IS a lean out condition, right? Should I spin the distributor back and retard it a bit, or should I just back out the idle screws a bit more? Or should I just switch the hose back to the manifold vacuum port. Or do I have my ass on backwards and the left is manifold and the right it timed? Sorry if this is confusing, it has been bugging me for a bit.
Backfiring is 98% of the time ignition. 2% any number of other things. The vacuum bib on the driver's side (in Arizona, USA*) is manifold vacuum. Run it where it works best for you. *(In Australia and UK it's the passenger side)
I guess it is a backfiring, but it isn't a single "BANG" noise, it is more of a POP......POP.POP.....POP..POP.........POP. (the ..... denotes pause).
http://www.roddingroundtable.com/dcforum/DCForumID1/4579.html I have the same problem, or pretty close to it.I have gone through everything I can think of and haven't figured it out yet.
If you have the '55 carb and are running the line to the port originally used for the Load-o-matic distributor, you will have REALLY strange problems with a later vac advance because this port puts out a certain amount of vac (venturi deprssion, actually) at full throttle! This will give you vac advance exactly when you don't need it. If one of the ports you are using is a threaded hole leading into two tiny passages in a '55 carb, plug that one off or at least plug its upper passage.
Oops--just realized you said the carb was a late Holley. Anyway, don't never nohow mix parts of the '49-56 Ford vac system with anything else!
Yeah, Bruce, I took that old 2 BBL off about 7 months ago. I had put the 57 dizzy in about 8 months ago. It ran so smooth with the 57 dizzy and 2 BBL, and I guess the advance had manifold vacuum then, now that I think about it. Well, anyway, I switched them back, so it gets manifold vacuum again on this Edelbrock so no more popping. The funny thing is that everyone suggested I try an Edelbrock because they are supposedly so much better right out of the box. Well, my Holley NEVER did any of this shit to me. I'd put it on, but I think 600 CFM is way too big for my 292.
Well, it started popping again today, so I've been playing with the mixture screws. It only happens when I let off the gas after the engine has been revved up. It is definately NOT popping through the carburetor. It is coming out the exhaust. Does anyone know what causes this, I mean the technical cause, too little fuel or too much? I might just throw my Holley 600 on and see if that one does it, but I really think that carb would be too big.
Backfiring through the exhaust is usually caused by an exhaust leak. When you wind it up, then let the engine pull it back down, it draws oxygen in through the leak causing any unburnt fuel to ignite in the exhaust.
600 isn't to big, just put it on for a day and see. Tuning tip, backfire out carb to lean, backfire out pipe to rich. Now just how bad is the pop, is it real loud or are you hearing the glasspacks rap? Hows your plugs look, sutty or white? -Jesse
BFT...OOOhh, alright, there are a couple of leaks in the system, whoever bent up this exhaust had a tough time with one bend (moron) and kind of hammered on it to get it right, it looks like the pipe made a crease and now, years later, that little crease spot has rusted through. Maybe it is getting worse on me. Jesse...It isn't the growl of the glasspacks, it really sounds like there may be too little back pressure (like a small Rice motor with a 3" exhaust) and at certain RPMs when you back off the gas it crackles and pops sometimes there is one pop that is really loud. I'll keep playing with the mix. I may throw that Holley on just for shits.
My 'ol Mopar always did that through tiny duals with a one barrel. I thought it was pretty cool and looked forward to any long downhills to get the most pop possible. Even more so before I had mufflers. Chris
It annoys the hell out of me and (I assume) reinforces the non-car guy opinion that an old car is a piece of shit. No, I really DON'T care what some Yuppie in a Benz thinks, but I would like to drive through neighborhoods without scaring children.
Without scarin children, have you lost your sand? I remember once when people prided them selves on how many children they scard(come on it's fun). Fix the leaks and putt the holley on, you never know you may perfer the holley. -Jesse
Oh, I wish this was a Holley. Everyone said that the Edelbrocks were so much easier to tune, well, I NEVER had this much of a problem with either of the Holleys that I used. I leaned it out a bit and it seems to have helped.
i had the same popping problem with my car...turns out the points just needed re-gapping...worth a shot i guess.
Whenever yer getting frustrated over carb tuning, again, do what I do: think of the debate between two men in the barbershop in the Cohen Bros. film "The Man Who Wasn't There": [verbatim]: "What you do, pump the gas some while starting it." "No, that's what the choke's for. Don't need to pump it, just keep the pedal to the floor and work the choke." " :...aaand pump it!" And if you haven't seen the movie, that's on yer to-do list. 'Tis my remedy.
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