Motor Problem???

OK guys here’s the problem, new to the whole boating thing and just rebuild my first boat. Took it for its maiden voyage last night after the rebuild. When running WOT I’m only hitting 3,600rpms. My buddy, who’s a mechanic, came over 2 nights ago and we had it running on muffs and was pulling 5,000-5,200rpms. I know there’s no resistance from the water but this doesn’t seem right to me. When running it towards the end of last year, when I got it, was getting about the same rpms and I just figured the tach wasn’t right. Any ideas of where to start/what to look for/at? Motor is an early 80’s Merc 40hp on a 17’ Sea Nymph Bass Attacker.

what do you mean you "rebuilt it"

what did you do to it?

give us the details so we can help you out

Never rev a motor like that out of the water. What pitch is your prop? Does it jump up on plane or take forever to get up?

Buy rebuilt I mean stripped it down to bare hull and it basically everything inside the boat is brand new.

It takes FOREVER to get up on plane.

I know it doesn't help but I'm not sure anything about the prop, I'll see if I can find any numbers on it to get any info.

Last year it was running 23-24mph on gps, last night of course I forgot my gps but didn't seem as fast.

allanlebar said:

Buy rebuilt I mean stripped it down to bare hull and it basically everything inside the boat is brand new.

It takes FOREVER to get up on plane.

I know it doesn't help but I'm not sure anything about the prop, I'll see if I can find any numbers on it to get any info.

Last year it was running 23-24mph on gps, last night of course I forgot my gps but didn't seem as fast.

Click to expand...

but what did you add to it? is it still in its stock form just with new stuff in it or did you load it down with extras?

Still in its stick form. I'd say it might be 40-50lbs heavier overall. I did add a CMC power tilt/trim unit as well.

Had the wife check the prop and she found this number 4879792 A4 12P I couldn't find anything about it. It is a stainless steel prop.

12P. 12" Pitch? Doesn't sound over propped. Carbs cleaned recently? Compression numbers?

after you added the CMC does the cavitation plate still sit where it should in relation to the bottom of the hull?

I can check compression and clean carb over the weekend.

Prior to CMC last year cav. plate was even w/ bottom of hull. Now it is 1" above (their specs say 1"-3" above bottom of hull)