popping: carburetion? ignition? or?

i was hoping i could get someone to help me troubleshoot the following.

400 small block up to 4500 rpm, 4150 mechanical double pumper with stock out of the box setup, stock distributor with new hei in-cap and rotor, solid copper core wires, accel shorty plugs non-resistor.

i would take the nova out for a drive, and the engine fully warmed up. normally i drive with the lightest foot... and everything's fine. but under hard acceleration, opening up the carb to WOT, i would occasionally experience what sounds like a tight metal cable snapping loudly, what feels like the engine stopping for a moment, and then continuing normally.

i thought i was lean for a while... i checked the plugs and they seem to read fine; i compared them against a chart of what good, healthy plugs should look like vs. warning sign plugs. i've tried solving this problem in the past by running a larger secondary nozzle, but no dice. i stepped up the secondary jets 1 size up.. but still no dice, and the plugs started showing signs of richness.

afterwards, i thought it was because i was running 87 octane. however, i remembered this happening as well even when i ran 93 regularly.

i'm thinking it might be ignition, but i don't have any experience with ignition systems, and i don't have the troubleshooting experience to know where else to look other than what's above.

do you guys have any suggestions what i should be looking for/trying next? opinions?

Reply to
Gerard
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A leak in the exhaust system.

Dave Baker - Puma Race Engines

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I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though.

Reply to
Dave Baker

it's not a leak in the exhaust system, because i am using open headers; i don't see how a leak at the header flange would cause the engine to stall and/or make a loud ping noise. my guess is still ignition misfire, running out of gas at the top end, or stuck timing.

Reply to
Gerard

Try buying/installing a good advance curve kit for your mechanical advance weights in the dist. Follow directions and be SURE to set initial timing correctly--which may or may not be accurate via the harmonic balancer. You'll prolly need to experiment a little--too long a curve you'll either be sluggish off the line(timing retarded to not pop back at high rpm) or else popping at hi rpm(timing advanced to come off the line strong). If curve is too short, well, ain't nothin' gonna run right--most likely not one of the options in the kit!!! But just right, it'll feel almost like a new cam/carburetion! HTH & good luck. sdlomi

Reply to
sdlomi

An exhaust manifold leak can cause strange popping noises. Almost like a backfire, but not quite.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Gerard wrote:

Reply to
Mike Romain

The leak allows some unburned fuel to ignite in the header pipe and will make a pop.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Gerard wrote:

Reply to
Mike Romain

thanks, interesting. i hope it's not a leak, since i use those dead-soft copper gaskets which cost a pretty penny over paper ones. i used those because i met a lot of people at the track who swear by them.

however, in another thread, i think we're getting the problem nailed down to carburetion/misfire.

Mike Roma> An exhaust manifold leak can cause strange popping noises. Almost like

Reply to
Gerard

A piece of tubing held to your ear and run along the headers would quickly eliminate that as a possibility anyway.

It is a sneaky one.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Gerard wrote:

Reply to
Mike Romain

yeah, i've had leaky exhaust plenty of times before, and this definitely isn't one of those times. thanks though

Mike Roma> A piece of tubing held to your ear and run along the headers would

Reply to
Gerard

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