340 Running super weird

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You have rapidly advancing timing so yes put it back to where it was. As usual with these kinds of problems, start with a basic tune-up and go from there.

ps I'm not sure if I am one of the anointed 'smart guys' but take all internet advice with a grain of salt :)
 
The answer to your question with the limited amount of info we have been given is:

You now have to start with a series of checks to reinstate everything back to the way it was or an oem setting on the distributor itself, then physically finding top dead Center number 1 on the engine, re-installing the distributor with an approximate 10 degrees advance on it, putting back the distributor cap and ensuring all the plug wires are in the correct order, then starting it, warming it up, checking base timing with vac advance hose off and plugged, set base timing to 12 or 14 or whatever your car liked before, then taking a vacuum gauge out and setting idle air mixture screws for peak vacuum and engine rpm, once found enriched the screws about an 1/8 turn at most, just slightly richer than peak.

All of this should put you back to your happy spot.

Good luck
 
"Clears up, but comes back", over advanced timing never "clears up", it either is or it isn't. Advance weights or plate sticking, fuel issue, or component/voltage issue...
 
1MeanA said:
You have rapidly advancing timing so yes put it back to where it was. As usual with these kinds of problems, start with a basic tune-up and go from there.

ps I'm not sure if I am one of the anointed 'smart guys' but take all internet advice with a grain of salt :)
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We are all guessing at this point. Who knows what his tune up buddies did to the engine. :BangHead: :BangHead: :lol:
 
Sorry I haven’t responded to anyone, so let me give a little more info on the set up, I’m very familiar with the car as I built it myself, it’s a 73 cast crank 340, with a cam intake and carb and that’s about it, nothing fancy, the distributor is a stock style electronic distributor, I swapped that spring back to the way it was and put the advance limiting plate in the 18 degrees of advance slot and set the initial at idle at 16 degrees advance, with the timing light on it and getting the rpm’s up to around 2500-3000 it’s going beyond 34 degrees total timing. The vacuum advance is blocked off, I’m not using it, and the issue is still there, I have undone everything that was done by my friends so I think next weekend I’m going to do a compression test and a leak down test and see what I come up with there. I pulled the valve covers and took a look and everything looks good, no bent pushrods, it has stock stamped rockers. I’m getting a little concerned that whatever the issue is that it could ultimately hurt the 340 and id hate to toast a 340. One quick note, when I first purchased the advance limiting plate I set it up wrong(or maybe right since it ran good) I put it on the 10 slot and set the timing around 15 degrees initial, so maybe since it allowing more advance that worked out setting the advance up lower back then. I’m super lost here guys and I’m sorry for lagging on the replies, I greatly appreciate everyone’s input and I’ll do my best to get back to any questions or info yall need, I store the car about 45 minutes from me so I can only work on it on the weekends.
 
Greenmachine225 said:
Sorry I haven’t responded to anyone, so let me give a little more info on the set up, I’m very familiar with the car as I built it myself, it’s a 73 cast crank 340, with a cam intake and carb and that’s about it, nothing fancy, the distributor is a stock style electronic distributor, I swapped that spring back to the way it was and put the advance limiting plate in the 18 degrees of advance slot and set the initial at idle at 16 degrees advance, with the timing light on it and getting the rpm’s up to around 2500-3000 it’s going beyond 34 degrees total timing. The vacuum advance is blocked off, I’m not using it, and the issue is still there, I have undone everything that was done by my friends so I think next weekend I’m going to do a compression test and a leak down test and see what I come up with there. I pulled the valve covers and took a look and everything looks good, no bent pushrods, it has stock stamped rockers. I’m getting a little concerned that whatever the issue is that it could ultimately hurt the 340 and id hate to toast a 340. One quick note, when I first purchased the advance limiting plate I set it up wrong(or maybe right since it ran good) I put it on the 10 slot and set the timing around 15 degrees initial, so maybe since it allowing more advance that worked out setting the advance up lower back then. I’m super lost here guys and I’m sorry for lagging on the replies, I greatly appreciate everyone’s input and I’ll do my best to get back to any questions or info yall need, I store the car about 45 minutes from me so I can only work on it on the weekends.
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I will definitely go back next weekend and reset everything back to where it was before they touched it, I’ll find TDC on cylinder 1 and go from there and start from ground zero with the carb tuning.
 
Well then its actually a Chrysler distributor with a FBO plate. If its a MP distributor the original curve was pretty good but the timing at idle rpms may need tweaking for a hot cam. Based on the information now, such as not using vacuum advance, I don't think timing is the issues your describing.

If you're interested in the timing advance curves, see my links in this thread Having fun with timing All the links are small block examples (even though the OP is working with a 383) with Chrysler advance mechanism.

If its not an DC or MP distributor, then its likely the initial advance is long and fast. The FBO plate can't correct that because it limits the advance at higher rpm instead of addressing the low rpm portion. But without vacuum advance it should be OK even with the limiter plate. And if you do everything the way Don recommends and use his springs it should work out in the end - at least I would think so - I haven't proofed it myself.
 
No surprise it's going beyond the 34 degrees. They all do it. None of them limit the advance correctly and several people have told him about it and he refuses to believe it and refuses to correct it. This is why I keep recommending to weld the slots and file them back out to where you need them. .......not that any of that is your issue. I just wanted you to know you ain't the only one with that issue. They're all like that. I think you're on the right track with the compression test. Keep us posted.
 
RustyRatRod said:
…This is why I keep recommending to weld the slots and file them back out to where you need them….
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That’s the way a local shop used to do it. They had a Sunn machine to spin them up I believe. They are long gone unfortunately.
 
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