4.3 merc prop or engine advice

[Chuckles88]

1989 4.3 merc. New plugs cap and rotor. Timing is on. I was running a slightly chewed up 14x17p 3 blade at 4700 rpms at 37mph. I found a great deal on a 21p high 5 and got 41mph at 4400 rpms. The high 5 had great acceleration and handling. Am I too low on the revs? Re-jet the carb for my altitude at 4200'? Find a different prop? Not worry and run it? Thanks

 

[achris]

By spec 4400 is borderline. Rejetting won't increase the rpm. Merc doesn't recommend rejetting anyway, just change the prop to get the revs back up.. Personally, I'd find a lower pitch prop...

 

[Chuckles88]

It seems to run slightly rich. I'm sure it is altitude. Could new plug wires help? Higher octane fuel? I run ethanol free 87. I've looked into props and wow is it a rabbit hole.

 

[Rick Stephens]

I would not rejet. I run from to and between 700 ft and 5k altitude, and I wouldn't rejet for 5k. Seems to me you need a 19 inch High 5 with how the 21 is working.

 

[Chuckles88]

Thanks for the replies. Now, I need to find someone who would trade.