Logo
FULL SITE MENU

1989 TJ150SLCEM Johnson 150 GT RPM problem.

D

Drewman521

New member
I would be eternally grateful if someone can help me with a problem I'm having with my 1989 Johnson GT 150 HP motor on my older Nitro boat.
Last year, I had a problem with the motor not having the power to get my boat on plane. I paid a licensed mechanic over $1,100 to work on the boat. It look 6 months and when I finally got it back, I have the same problem. Needless to say, I really don't want to take it back to him.
The problem I'm having is my motor runs fine in the yard with the muffs on... I can get almost 4,000 on the tac, however, when I put it on the water and it's under load, I barely get 2,000 RPM and the boat will not plane. I have replaced the plugs, had the carbs rebuilt, replaced the fuel filter. The plugs have been fouling and the motor smokes more than I remember it doing. It also smells like the motor is flooding. From what I have been reading, the problem may be the VRO pump. I would like to look at all other possibilities as a replacement pump is in the $350-400 range.
I have googled the problem until I'm cross eyed.
I would be eternally grateful if someone could point me in the right direction.
BTW, I have not checked the screen in the tank. I'll be doing that tomorrow. I have thought about replacing all of the hoses just to make sure it's not a problem.
Thank you very much.

Andrew.
 
First things first.....

Compression check ?
Spark check?
Coil primary wires on the proper coils (Blue sky/ Green grass) ?
Timer base not stuck, rotating fully to the stop when you advance the throttle ?
Carb throttle plates opening all the way when control box is in the WOT position?

Check all the above, in the order posted, and report back.
 
Wow, quick replies.
Additionally, here's what I know (I certainly would not claim to be a boat mechanic, so excuse any mistakes). The motor is a low compression motor. All cylinders are 92-95 PSI I believe. I originally didn't have spark in all plugs and the mechanic replaced the CDI box. I believe be also replaced the coils. I hope he put the wires on correctly. Thanks for the advice Fishwrench. I hadn't heard about not revving it over 2 G with muffs on. I was trying to figure out why I got near 3.5 G with muffs on and half that under load. I don't know about the carb throttle or coil wires. Like I said, the mechanic replaced the coils I believe.
When the mechanic and I were on speaking terms, he suggested a different prop (my motor has an original shooter prop 13.5 x 23PP). He allowed me to borrow a 14.5 x17PP and it didn't make a difference. Not enough power to turn either one. I know my original shooter prop is more for speed, but the other prop didn't make a bit of difference. I can get on place if a friend of mine weights the front of the boat down..... after about 30 seconds. I have also noticed a drastic drop in power when I do get on place the occasionally makes me fall off plane. The motor spits and sputters a alot.
I had gotten a long constant alarm at one point and shut down the motor. The motor does die on it's own alot also when idling.
I did read a post someone else on this motor where someone had replaced all of their lines (oil and fuel) and resolved the problem. I had thought of doing that since it's a bit cheaper than replacing the VRO. I had also thought of remixing fuel and oil and bypassing the VRO, however, I had read differences of opinion about dong that.
I hope that helps clarify my situation.
Thanks much for the quick replies.
 
Oh, one other thing I noticed when going through it last night is there appears to be a small amount of oil inside the motor case near the hose for the oil where it enters the motor. Is that normal??
 
I thought I would post an update on my progress. I replaced all of the fuel lines and checked my fuel tanks. I then noticed there was a plastic part that fits up into the fuel pump that apparently has come loose. It originally was pressed into place in the factory I would guess. I pulled out the pump and used SEAL ALL for gas and placed the part back where it was supposed to be. I suspect it was sucking air when under load as it was not making a tight seal. I hope to be able to run it this weekend. I'll report back in hopes it helps someone like me.
 
The piece that came loose , what did it look like ???-----------rectangular piece about 1" wide 2 " long ??---Any o-rings visible ?
 
Back
Top