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Discussion Starter #1
I am having trouble with engine running with intermittent stumble, and running slightly rough with vacuum advance connected. When I disconnect it runs smooth. My timing is set at about 12* Any input would be appreciated.
 

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I am having trouble with engine running with intermittent stumble, and running slightly rough with vacuum advance connected. When I disconnect it runs smooth. My timing is set at about 12* Any input would be appreciated.
I am having trouble with engine running with intermittent stumble, and running slightly rough with vacuum advance connected. When I disconnect it runs smooth. My timing is set at about 12* Any input would be appreciated.
I am having trouble with engine running with intermittent stumble, and running slightly rough with vacuum advance connected. When I disconnect it runs smooth. My timing is set at about 12* Any input would be appreciated.
I am having trouble with engine running with intermittent stumble, and running slightly rough with vacuum advance connected. When I disconnect it runs smooth. My timing is set at about 12* Any input would be appreciated.
At what rpm does the stumble and running rough occur? And does your engine have its original harmonic damper?
 

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Discussion Starter #3
At what rpm does the stumble and running rough occur? And does your engine have its original harmonic damper?
Stumbles at idle, stumbles up to around 2500 just has intermittent miss, goes away past 3000 . I don't know about the harmonic dampener though. Too much advance?
 

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Stumbles at idle, stumbles up to around 2500 just has intermittent miss, goes away past 3000 . I don't know about the harmonic dampener though. Too much advance?
When the outer ring of a damper slips the timing mark ends up in a retarded position. So when you time it using that mark it ends up being way too far advanced. You can make a piston stop out of an old spark plug by breaking all of the porcelain out then welding a 3/8" bolt into it with the the threaded end protruding about 3". Remove all of the spark plugs then install your piston stop into the #1 hole. Bar the engine over by hand (DO NOT USE THE STARTER). Or you can grip the flex plate (or flywheel) with Vice Grips to turn the crank. When the crankshaft comes to an abrupt STOP the #1 piston is hitting the bolt. Mark your damper in that spot then turn the crank the opposite direction until the crank comes to an abrupt STOP. Mark the damper in that spot and your real TDC is between those two marks.
 

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Stumbles at idle, stumbles up to around 2500 just has intermittent miss, goes away past 3000 . I don't know about the harmonic dampener though. Too much advance?
As your harmonic damper is over 40 years old it needs to be replaced. Every firing pulse puts a shock load on the damper's outer ring and over time the outer ring finally slips out of its original position. Once it slips it's impossible to set the timing accurately so the only solution is to replace the damper. Remove your fan then set your car on safety stands and work on it from the bottom. You can remove the damper by using a 3 slotted wing puller and then to install the new damper you MUST use a damper installer which you can rent from any AutoZone.
 

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Discussion Starter #7
As your harmonic damper is over 40 years old it needs to be replaced. Every firing pulse puts a shock load on the damper's outer ring and over time the outer ring finally slips out of its original position. Once it slips it's impossible to set the timing accurately so the only solution is to replace the damper. Remove your fan then set your car on safety stands and work on it from the bottom. You can remove the damper by using a 3 slotted wing puller and then to install the new damper you MUST use a damper installer which you can rent from any AutoZone.
Lethal, no I haven't done anything that would have disturbed the harmonic dampener if that's what you mean. I put headers, and a performer intake on the engine, but that shouldn't change things.

TBTR, I understand what you are saying, but the engine was rebuilt about 15000 miles ago, so it stands to reason the HD should be good.
Yesterday I retarded the timing 4* to about 8* BTDC, and it runs smoothly. The thing is, by doing so I have reduced the total timing in order to accommodate the vacuum advance. I really don't feel the difference with, or without the vacuum advance. I'm considering doing without it to improve my total timing. What say you TBTR, or Lethal? Other than the intake and headers it's a stock L48
 

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Lethal, no I haven't done anything that would have disturbed the harmonic dampener if that's what you mean. I put headers, and a performer intake on the engine, but that shouldn't change things.

TBTR, I understand what you are saying, but the engine was rebuilt about 15000 miles ago, so it stands to reason the HD should be good.
Yesterday I retarded the timing 4* to about 8* BTDC, and it runs smoothly. The thing is, by doing so I have reduced the total timing in order to accommodate the vacuum advance. I really don't feel the difference with, or without the vacuum advance. I'm considering doing without it to improve my total timing. What say you TBTR, or Lethal? Other than the intake and headers it's a stock L48

What you are describing is the symptoms of a slipped damper outer ring. Engine rebuilders only replace harmonic dampers when they are specifically asked to do so.
 

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Discussion Starter #9
What you are describing is the symptoms of a slipped damper outer ring. Engine rebuilders only replace harmonic dampers when they are specifically asked to do so.
Ok, maybe so, but retarding it by 4* seemed to do it. It runs better now with vacuum advance connected. I still would like to do without vacuum advance. Maybe the weight springs could be replaced with lighter ones, or stretch the old ones. I'm not gonna try it myself at this point, but I'd like more info on doing without vac advance.
 

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Ok, maybe so, but retarding it by 4* seemed to do it. It runs better now with vacuum advance connected. I still would like to do without vacuum advance. Maybe the weight springs could be replaced with lighter ones, or stretch the old ones. I'm not gonna try it myself at this point, but I'd like more info on doing without vac advance.
I wish you the best of luck.
 
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