Can't reach correct RPM's at WOT

[Chris the Prop]

I have a 76 Galaxy 16' with a mercruiser 120. I bought the boat with a bad motor, and replaced with a 1974 motor that had been rebuilt a year ago. The prop I had was a 14.5 x 21 and was shredded, looked like it had been used to till the garden. The best I could get with this was 3000 rpm's.

I replaced the prop this weekend with a 15x19, thinking that would boost me in to an acceptable range (spec painted on the engine is 3700-4300) but still top out at just over 3000 RPM's, and it takes a LONG time to get there, at WOT, it starts at 1800 RPM's and slowly climbs.

Compression is OK for an older motor 115,115,110,115. so I think that's ok.

I've heard all sorts of fixes, including bad gas, the coil, timing, and even the wrong cam used in the rebuild.

Anyone got any idea on the most likely, otr the order in which I should try different fixes?

Any help is greatly appreciated.

Thanks!!!

 

[Brucetafer]

Re: Can't reach correct RPM's at WOT

start with cheap stuff... bad gas, easy... redo all your fuel filters, pickup.. timing is huge, if its not advancing at the proper RPM its not going to do anything at 2K+...

also, what motor is it?? that would help... did you do check the compression correctly? WOT and 4-7 full turns? if you did, those numbers are low... most motors get tired at around 120-130... post back let us know..

 

[Chris the Prop]

Re: Can't reach correct RPM's at WOT

the motor is the 183 GM. Not sure about the compression, was checked by a local mechanic friend, I assume he did it correctly. (he maintains his own boats in top shape)

I'll try new gas and filters this weekend and see how that turns out, and we'll go from there. Thanks!

 

[searay3]

Re: Can't reach correct RPM's at WOT

As mentioned, check the distributor weights to make sure they are not rusted. Pull the cap and move them with your fingers. Should move freely against the light springs..