Prop question

[66stoney]

I'm looking for answers, I have always been an i\o guy but decided to get combo fish ski last year with a 150 Johson out board. My question is I have a 1998 Glastron 185 fish\ski with 150 hp Johnson Intruder Ficth Injected, boat came with a 4 blade 23 pitch stainless prop but boat would not get on plane & only get 2600 rpm's. I tried a 3 blade aluminum 19 pitch & got 3800 rpm's & around 35 mph. How low of a pitch prop will it take to get me up to 5500 rpm's & 3 blade or 4 blade?? I have freinds with similiar style boats & motor & they are 19 to 21 pitch but that's not working on this boat. The cavitation plate is about 3/4-1 inch higher then bottom of hull so that looks good.

 

[steelespike]

Re: Prop question

I think you have more problems than a prop. you would need to drop about 8" of pitch putting you at about 11" that's smaller than what you would put on a 25ft pontoon. You probably have a motor issue.
Could be as simple as a plug wire off,maybe the throttle not opening all the way.
A compression check wouldn't hurt.

 

[jestor68]

Re: Prop question

What steelespike said. That motor should not be breathing hard to spin a 19" prop to at least 5000 rpm pushing a 1500 lb boat. But since your rpm range is 4500-5500; you only need to get to 5000 ( not 5500 )to develop full power.

You need a mechanic(versed in Johnson V-6 motors).

 

[66stoney]

Re: Prop question

Had it at boat shop & it was on the dyno for 54 minutes & only code it showed was water in fuel a few times, had to replace power pack this spring so fuel has been in it since April. The throttle seems correct as I can get higher rpms when I trim it way up but it is washing out at the height.

 

[jestor68]

Re: Prop question

Had it at boat shop & it was on the dyno for 54 minutes & only code it showed was water in fuel a few times, had to replace power pack this spring so fuel has been in it since April. The throttle seems correct as I can get higher rpms when I trim it way up but it is washing out at the height.

What kind of hp numbers did it show on the dyno at 5000 rpm?
Did they check comp at that time and show you the numbers. There aint no code for low compression. A 16 oz. bottle of STP gas treatment would take care of the water in gas issue.