21' 3600# W/ 280--Thinking I need to change prop--appreciate advice from expirience

I bought this boat with a newly installed rebuilt motor. Thinking it's over propped a little. It has a hard time getting up w/ tabs down and regular load (my wife and two kids) forward, but once it's up it does ok.

Here's what I know: drained old gas and put new 92%octane in, did sticky recommended fuel system check and replaced fuel line and doped the fittings good to go no bubbles and good flow, replaced fuel/water filter. Motor seems to be sweet and rips, I think I could rev to 5k but didn't--linkage is good I think.

Current prop is 15x19 3 blade and my dad went out with me and thinks it's over propped. once up WOT is 3500 and about 35mph (based on sensor??) Would ya'll suggest a size smaller or a 4 prop. Let me know if I need more info. Thanks!!

Re: 21' 3600# W/ 280--Thinking I need to change prop--appreciate advice from expirien

Whidbey, give your engine specs here for better advice. I can guess that it is the 5.7 you have been working on but repost all that please so all here can understand the situation.

Re: 21' 3600# W/ 280--Thinking I need to change prop--appreciate advice from expirien

Sorry. Yes, 5.7LG serial#10054727. Looks like everything from the previous Volvo Penta 570 bolted up, including Holley 4 barrel. Let me know if you need more info, and I'll try to figure it out. Thanks Maclin!
Also, it's a deep V 21' GlasPly.

Re: 21' 3600# W/ 280--Thinking I need to change prop--appreciate advice from expirien

Is the 3500 at wot?
A 19 seems like a reasonable size for a 280 on a 3600 lb boat.
If 3500 is wot your 1500 rpm short that would require a 7" reduction in pitch putting you at about a rediculess 12" pitch.
What year is the boat?Does it respond to up trim?' Don't assume because its a new setup that everything is right.
Could be as simple as a plug wire off.
If the motor is ratted for 87 octane 92 is a waste and may even slow the motor.

Re: 21' 3600# W/ 280--Thinking I need to change prop--appreciate advice from expirien

Yes, 3500 is wot. It's a 91. I need to work with the trim tabs a little more to know for sure. The motor just really bogs at take off and then maxes out at 3500, but sounds strong at that. I do use the tabs + everyone forward to get on plane. Thanks on the 87 vs 92 octane, figured it might help but could use to save anywhere possible. Hmm? The motor just seems underpowered, maybe that's why the original owner offed it after putting in the rebuild. figured it might help to go with a four blade, glad I asked first. I'll check the plug wires, and try to find a good mechanic around here. Let me know if you have any suggestions. Thanks for the reply.

Re: 21' 3600# W/ 280--Thinking I need to change prop--appreciate advice from expirien

Make sure the carb has full throttle travel.

I think a 19-21 pitch should be close to ideal and let the engine get to 4500 rpm if it was running correctly, maybe even a 23. Those engines were rated at 275HP at the engine, probably 230-240 at the prop. The one in my 22 footer really goes. Hard to compare the pitches between our drives since mine is a DuoProp, but the numbers I get show a 21-23 range in a prop calculator.

Re: 21' 3600# W/ 280--Thinking I need to change prop--appreciate advice from expirien

and I totally agree on running "just" 87 octane, that is the spec for the AQ271C and also the 570.