I have been driving my 8BA powered roadster since last October. Every now and then it would have a deceleration pop in the exhaust. This past summer it has gotten a lot worse and annoying. The car runs strong and has good power. It is an old original 2x2 edelbrock intake with a pair of stromberg 97's. The past 2 months the pop has gotten worse and I was worried it could be a bad valve. The other night I did a compression test just to get a baseline. I did the test with the engine cold and at WOT. All 8 cylinders had 130 lbs plus. The spark plugs were black and the car seemed rich so I changed the main from 46's to 44's. I drove the car and the plugs are cleaning up and look nice and brownish white on the porcelain. Still had the Deceleration pop and was doing it at idle. I went ahead and checked the floats and they were a little low so I raised them to 15/32" like they call for. I installed a vacuum gauge and adjusted the idle screws. When I lean the carbs the popping goes away at idle but the vacuum drops. The car is still popping on deceleration and I am open to ideas from the experts. Should I do a leak down to confirm it's not a valve sticking? I am tempted to install a stock 8ba intake I have with one carb to see if it's induction. I am running a mallory dual point distributor. Any help or pointers would be greatly appreciated. Thanks, Jim
Also the car has headers and a short exhaust system with no mufflers. It only seems to pop out of the left bank and not the right.
My 292 powered Chev C-20 does that, it is an exhaust manifold leak that draws in air on deceleration and burns (pops) the un-burnt fuel in the exhaust gasses
I have read some posts about exhaust leaks popping on decel. I checked the header for leaks and don't feel any. I guess I will pull the exhaust and header off the drivers side and check it for pinholes and leaks. I wonder if a really short exhaust is making it worse. Thanks Posted using the Full Custom H.A.M.B. App!
That lean pop under the high vacuum at idle and on decel can also be an intake leak. If it's just on one side, maybe one cylinder, try to determine which one and then if it's leaking around the manifold gasket, carb base or hope it's not a crack. jack vines
Thanks, I'll check the intake and carbs. I sprayed some windex where the spark plugs screw in the head while it was running and noticed the rear spark plug was leaking around the threads pretty good. Going to try and seal it up. Posted using the Full Custom H.A.M.B. App!
It sounds like you're still running rich if it's popping still. When's the last time you did a carb kit on it. Another thing to check is the abnormal smell of raw fuel or I burned fuel coming out of the exhaust. Posted using the Full Custom H.A.M.B. App!
I feel it is rich still at idle. I haven't done carb kits but they looked new in October 2013 when I put the carbs on the intake. The car doesn't smell fat at all when at cruising speed like it did with the 46 jets. Posted using the Full Custom H.A.M.B. App!
Then I'm with Packard v8 it sounds like an intake leak. There could be a hairline crack at the base of your carb or the intake manifold Posted using the Full Custom H.A.M.B. App!
Thanks guys for the input. I will check out the intake and carbs for cracks/ leaks. Jim Posted using the Full Custom H.A.M.B. App!
Get starter fluid and spray it around the base of the carb and onto the intake manifold. If the engine accelerates then you found your leak Posted using the Full Custom H.A.M.B. App!
Short exhaust systems are prone to doing that because cold air hits an exhaust valve and makes it change shape a bit until it lets go under pressure. Not a good thing because you are warping the valve a little more each time it pops. Not a big deal on race engines because they usually get torn down before the valve gets in such bad shape that it blows.
The exhaust exits right at the rear tires. I don't think the short exhaust is the cause of the problem because it only does it on the drivers side. I do want to fix the backfire issue so I don't hurt the engine. Posted using the Full Custom H.A.M.B. App!
Adjusted the carbs and got the car to pop on idle again. Went thru and pulled one plug wire off at a time. When I got to the front plug on the drivers side I couldn't get it to pop with that wire off. As soon as I put the wire on it would pop again. I'm hoping I am narrowing this problem down to that cylinder. Posted using the Full Custom H.A.M.B. App!
That pop is what we used to call "Backing off" in the old days. we thought it was a cool sound. we got it by pulling out the choke at decelleration. that's how we got it. My car runs a little rich all the time and it's been popping for years and many miles! If you experience this with throttle closed and on one side only, maybe you are running to rich at idle on one side. try leaning out that side of the carb. just my $.02
Be careful with the starting fluid on a hot engine. Ethyl ether is highly flammable and that could end up very badly for you and your ride.
Just watched down the carbs real careful with the air cleaners off and noticed the front carb is dripping out of the booster at idle. Time to figure out what's going on with that. Posted using the Full Custom H.A.M.B. App!
My first 8BA had pennies in the heat risers, when I adjusted my valves I pulled them out. The pop on deceleration stopped don't know if it was the pennies or the valve adjustment. Tony
Well, I threw another clean 97 on that I had and the abrupt pop is gone and now its just more of a mellow gurgle. I think its time to order some rebuild kits for the carbs and freshen them. Thanks for everyone's input and happy 4th! At least I got to go bombing around the neighborhood in the roadster today while I screwed around with it. Posted using the Full Custom H.A.M.B. App!
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