RPM's on my Alpha One

[SeattleParamedic]

I have a 1995 3.0LX Alpha One (181 CID) 4 cylinder, 135 horsepower (the lower drive is Alpha 1.98 ratio B) in a Larson SEi 174 (17.5 foot) bowrider. I bought the boat used and my WOT rpm is only 2200 (book says 4400 - 4800) and at the 2200 rpm it does 43 mph. This is with a 4 blade 14 x 20 pitch prop. Could my tach be reading wrong or am I THAT over propped? Or could my WOT be that far out of adjustment? Thanks for your help and comments, and prayers to my brothers and sisters and their families in New York.<br />Jim

 

[Fouled Plug]

Re: RPM's on my Alpha One

I would guess your tach is out of adjustment. What does it read at idle?

 

[SeattleParamedic]

Re: RPM's on my Alpha One

Fouled Plug:<br />The tach seems to be accurate at idle as it reads 650 to 700 rpm. To check it, I was going to get my dwell/tach, connect it up and compare the readings at various throttle positions tomorrow. I will let you know those results. Assuming the tach is correct, what next? Thanks, Jim

 

[Fouled Plug]

Re: RPM's on my Alpha One

That does sound like a lot of prop for that boat. Is there a dealer in the area with a loaner prop you can try? He can probable suggest a good place to start with your current info. I have a 17' cuddy with a 90 Yamaha and I run a 13 1/2 x 15. The speed for your RPM is pretty impressive, but you're lugging the motor big time if that's WOT. Try another wheel with less pitch and diameter and see where your rev's are.

 

[ODDD1]

Re: RPM's on my Alpha One

Lets see...17 foot boat, about 140 hp, 43 mph...your tach is definately lyin to you...40mph on that boat would be good...dont change the prop...fix the tach....

 

[SeattleParamedic]

Re: RPM's on my Alpha One

Yes, the horsepower is 135... and as a note, it does not sound like the motor is being lugged at all, but what do I know.... it's my first boat. Thanks for the continued responses and I'll let you all know what the dwell/tach says tomorrow.

 

[Fouled Plug]

Re: RPM's on my Alpha One

By the way, how are you measuring speed? Does if feel like 43 to you? Maybe the tach is right and the speedo is lying.

 

[SeattleParamedic]

Re: RPM's on my Alpha One

Fouled Plug:<br /><br />Good point... I am going by the stock speedo which is integral to the lower drive Mercruiser unit. It does seem to be accurate in my estimation.....