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Ditto Mark on that!................ just make sure the advance curve is close to the factory curve; marine engines see a lot more load than a road engine and won't tolerate excessive advance.
These two return spring values are never the same......... it's part of the design........... I have a IBM 7007-S. I found the springs are mismatched. One spring has no real spring or tension and is much bigger than the other. See pics of how I found it and the two springs side by side for comparison.
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I have replaced the bigger with one that may be a little stronger than the other small spring. But now the boat runs for crap. (That's really not new though. Does anyone have a good picture of the springs & weights in the prestolite? Also, how can the advance curve be checked? Does this require a specialty machine?
Ditto again!................... If the springs are shot, best bet is to remove the entire distributor and take it to a 'hot rod' shop. Explain to them the application and make sure you are confident that they understand this is a marine application. They can 'dial in' the advance curve based on both the springs and the weights, yes, using a specialty machine. Another approach to determining the curve in the distributor is to get a timing tape and a timing light and measure it. With the engine "not running well", the measurement method may be suspect.
FWIW, a bad spet of springs or sticking weights will mess up the advance curve and generate poor ot very poor performance.
I would like to know more about the springs in the prestolite distributor also. I have a IBM 7007-S. I found the springs are mismatched. One spring has no real spring or tension and is much bigger than the other. See pics of how I found it and the two springs side by side for comparison.
View attachment 3044View attachment 3045
I have replaced the bigger with one that may be a little stronger than the other small spring. But now the boat runs for crap. (That's really not new though. Does anyone have a good picture of the springs & weights in the prestolite? Also, how can the advance curve be checked? Does this require a specialty machine?
Please, please, please....... do not haphazardly change flyweight return springs without at least plotting out your NOW Progressive Advance curve along with your TA.
Plot this out in graph form and on paper..... and compare it to your OEM advance curve!
Weak and/or rust compromised return springs, or an incorrect value replacement spring may cause an early and aggressive ignition advance.
Such a scenario will definitely lead to detonation !!!!
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