My old school 340 upgrades and results.

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Thanks for the compliments. It does have a mechanical pump in addition to pusher pump near the fuel cell.
 
check the pickup gap in the distrib. - less than .008" will act like a rev limiter - sputtering and banging
 
Here is a video of the popping at high rpm. Not sure how it will translate over video.
 
Definitely sounds like an ignition or valvetrain issue since it does it when free-revving, if it was fuel it would only happen under load. May just be me but it sounds like it starts breaking up between 4-5000 RPM and it's almost like you have a rev-limiter at 6000. Dumb question but what's the rev-limiter set to on that MSD box?

Also check that reluctor gap in the dizzy that could be your culprit and it's super easy to do...
 
It is pretty smooth at 4 and 5. 5200 on up it starts to shoot ducks. It will still Rev passed 6 just not clean. I am not even close to holding the pedal to the floor. I don't enjoy revving it so high in neutral with no load though. I will check the gap. I may try putting a vacuum Guage on it and hold it at 5500. If it was valves the needle should bounce.
 
you mean cyl. # 1 spring ? cause that's not it if I'm seeing it right
 
oh, got it now :realcrazy:. Is it spitting gas up through the carb?
 
I would say by what I heard in the video, and what the symptoms are, it's electrical. I could very well be wrong. It's not fuel delivery, or it wouldn't do it until you are under load. You are running strong for short-shifting it. If it was a cam problem, it would show it's face by the performance it made. I say your electrical system is messed up, and I still say I would just do a MP electronic conversion kit. I've heard of some stories with MSD ignitions giving some problems (not hating on MSD at all). Just say'n.
 
318willrun said:
I would say by what I heard in the video, and what the symptoms are, it's electrical. I could very well be wrong. It's not fuel delivery, or it wouldn't do it until you are under load. You are running strong for short-shifting it. If it was a cam problem, it would show it's face by the performance it made. I say your electrical system is messed up, and I still say I would just do a MP electronic conversion kit. I've heard of some stories with MSD ignitions giving some problems (not hating on MSD at all). Just say'n.
Click to expand...
I agree with you 100 percent. I was going to do valve springs because of age and I probably still will eventually . I do not believe the problem is the springs. I decided this when I took the valve cover off last night and saw what I had. I agree that the fuel system would show itself more so under load. Not at light throttle free Rev.

I just went out to look at the distributer and not sure for sure if it is a Chrysler stock unit. It is similar but not sure. Here is a picture of the pickup.
 
yep, I think it looks like a stocker. However, the problem could very well be starting after the electrical tape that I see on the wires. Also, the fact that somebody was in there and stuck the curve, well, there is another opportunity. the allen bolt is a sure sign of some down home country tuning :) .I think your sniffing the right trail, but I would start from the tape (i'm saying your after market ignition system).
 
Reluctor looks different than most I have seen. Maybe anot early model or a mopar ignition kit the distributor is a cable drive tach model. The electrical tape is my work. The wiring was a mess inside the car. I shortened and cleaned up a lot of wiring. I don't know the gap because I don't have my feeler gauges here. They at work in my tool box.
 
Lustle said:
What kind of popping? Ignition? Valve float?

If you're running electronic ignition. I know the stock black box is supposedly no good above 5000 or so rpm.
Click to expand...

Supposedly might be the key word there, I run the black box, and mine pulls hard to 6500 on occasion, not a miss ever.
 
Do you know where timing is set at? Initial, and total? I set up a MP dist on my last 340 with close to 20 initial, I set the total by ear to break in a new cam and when I went for a test drive it sounded just like yours. Got It set at 34 total with a light and no more miss, rotor was jumping spark between terminals. Just something to check. Car sounds good otherwise.
 
Initial and total are both 34 checked with a dial back to 0 Mac timing light. Thanks I like the way it sounds as well. Even shifting at 5 it runs well. Thinking that once the issue is figured out and a few minor changes mid to high 11s should be doable .
 

Bad Sport said:
Supposedly might be the key word there, I run the black box, and mine pulls hard to 6500 on occasion, not a miss ever.
Click to expand...

Really? See and I've always been told that the black box is garbage. Need the orange box at least. I had problems with an occasional miss with my black box. Course I'm on a rev-n-ator now. And love it. Cleared up the miss.

Back to the problem. It's gotta be electric. But if it was always there. It's gotta be something that's been on the car for ages. It does almost sound like some sort of rev limiter.
 
I am thinking the pick up coil may be the issue . Just to simplify it I will dig into my parts stash and see if I can set up one of my old Mallory dual point distributors. I set one of those up on a sun distributor machine and I had solid reliable spark passed 4000 distributor rpm. 8000 engine rpm.
 
Sounds like timing is set at 34 total? If so, check rotor phasing. If you have an extra cap you can drill a hole between 2 terminals and run it, see if spark jumps between the terminals when revved up. Or another known good dist to try.
 
gtsdude said:
Sounds like timing is set at 34 total? If so, check rotor phasing. If you have an extra cap you can drill a hole between 2 terminals and run it, see if spark jumps between the terminals when revved up. Or another known good dist to try.
Click to expand...
The distributor is locked at 34. 34 degrees initial and total advance. If it was rotor phasing I would think it would do it at all rpm being as there is no timing change from idle to 6000+
 
Going on the ignition theory I would say it sounds like either the ignition pick up is not able to pick up reliably at high rpm, the MSD module not supplying enough dwell for the coil to fire that fast or the coil can't fire reliably at high rpm. I have seen similar sounding stock engines with bad coils or coils hooked up backwards.
 
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