1985 johnson 150 issue

[jlds913]

I have a 150 Johnson on a 18ft Ranger bass boat, My issue is that at full throttle it only turns 4000 rpm. I know that the plates on the carb are all the way open since I remved the cover to watch while someone worked the throttle, could this be a prop issue? It also has an electric fuel pump running 5 psi and the vro bypassed. Thanks

 

[JB]

Re: 1985 johnson 150 issue

Hi, jlds913.

Welcome to iboats. :welcome:

Sure sounds like an overpropped outboard to me. I will move this to the Prop Forum for the best advicce.

 

[BobGinCO]

Re: 1985 johnson 150 issue

Whatever your pitch is right now, you need a lower pitch prop.

 

[jlds913]

Re: 1985 johnson 150 issue

First off thank you guys very much for the fast help, The issue is im not sure what pitch is on the motor now. Would yall suggest a pitch? maybe 17 or 19? All i want is a little more power out of the hole to get the ole Ranger down faster. Maybe pull a tube or hydraslide once in a while. Also the boat runs about 45mph right now, if i go to say a 19 pitch will that number go up or down?

 

[BobGinCO]

Re: 1985 johnson 150 issue

You REALLY need to know what pitch is on it right now. Then make changes from there. If you've got a 19, maybe switch to a 17. But if you don't know your starting point, there's no way of knowing.

 

[jlds913]

Re: 1985 johnson 150 issue

Went home an pulled the prop. The only number I found were stamped on the inside of the hub. 024. Does this mean a 24" pitch?

 

[steelespike]

Re: 1985 johnson 150 issue

You need to make up 1000 rpm,that would mean about a 5" pitch change.Seems like a lot to me.
Your gps speed at 4000 rpm might give us an approximate prop pitch. A prop shop can measure the pitch for you.
No numbers under the prop nut?

 

[jlds913]

Re: 1985 johnson 150 issue

Took the boat out for a fast run. At WOT mph was 48mph at 4300 rpm on pretty smooth water and by myself. Sound about right?

 

[jlds913]

Re: 1985 johnson 150 issue

So heres an update, I pulled the prop off the boat and polished it up really good. Found some numbers on it that look to be engraved. The best i could make out is something like 14 1/4x24 and the 24 i can read clear as day just the other numbers are really worn, So this means i should have a prop with a 24inch pitch, Any suggestions on what pitch I should try?

 

[jestor68]

Re: 1985 johnson 150 issue

Yes that's a 24 pitch. You need a 20 or 21 pitch.

 

[jlds913]

Re: 1985 johnson 150 issue

So a 21 will get me to that target rpm of 5500?

 

[jestor68]

Re: 1985 johnson 150 issue

So a 21 will get me to that target rpm of 5500?

A 20 pitch Laser II should get your rpm up to 5000-5300, and 50-55 mph. Your '85 is 150 HP @ 5000 rpm, with a range of 4500-5500.

A fresh 150 would typically run a 21 or 22 on a 18 ft Ranger(not the fastest hull around), and crank out 5600-5700 rpm. I suspect your '85 is a little tired, unless it's been rebuilt lately.

This is an estimate; not knowing anything about your set up or the state of the motor.

 

[jlds913]

Re: 1985 johnson 150 issue

Thanks for all the help. I did a compression test on the engine when i first got and and all was about 110psi, I will get a 20"pitch prop and give it a try. Not really wanting all that much top speed just a little more out of the hole. I will fell much better getting the front end down when I have my family in the boat.