Also agree that if one change is to be made it should be a new prop. I would also look at the ignition system and upgrade to electronic (if it isn't already) and confirm that you are getting all the advance you are supposed to. I would also go through the carb as well.
Two 14" 5 lug S5 wheels with ST205/75R14 Kenda Loadstar radials $349
Two 14" 5 lug S5 wheels with ST215/75R14 Kenda Loadstar radials $389
Two 15" 5 lug S5 wheels with ST205/75R15 Kenda Loadstar radials $409
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CARBURETOR REBUILDING - $199
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