1986 Pro V 150 problem

[James]

Have a 1986 ProV 150. Boat was extremely hard to get up on plane. Had carbs rebuilt. Upon rerunning, it came right up on plane and ran good. After 10 minutes, it restricted itself to 4200 or so RPM. No warning buzzer sounded. (thought buzzer may have been bad) I then thought possibly overheating. I then installed a new impeller and thermostats. Took boat out today, ran great for several long runs. Motor then procedded to slowly lose RPM's down to around 4600 or so after about an hour of running.
Seems to idle smooth, cant figure it out. Dont think it has a throttle position sensor. It almost feels like its not opening up all the way. Checked the throttle linkage, seems to be working OK. Any ideas or tests to suggest would be great. Thanks for any input, James Aldridge

[jb123]

sounds like the carbs clogged again,because it did run fine THEN issue again. techs are suggesting the new 10 micron spin ons to prevent carb clogging particles.i put one on my 89 pro-v after 3 carb cleanings...knock on....fiberglass?

[Tractor-Tug]

i've been dealing with this on and off all season. its taken me three carb tear downs and cleanings to get it right, each time they have been dirty. if you recently started burning an ethanol blended gasoline that could be part of the problem. like jb said, i think we will both be looking at better filters.

i was a little intimidated at first myself to do so, but with a manual, the carbs are a snap to tear down, clean and rebuild, if you are moderately handy with a wrench.

[Ken]

James,
After running great for an hour, and then slowly dropping down to 4600 rpm - kinda sounds fuel related. Maybe high speed jets getting clogged a little.
I would take it back out and run it again to see if it will only come up to 4600. If it takes another HOUR before it acts up, then there has got to be some kind of thermal related problem.
If it acts up right away, then clogged jets, or maybe weak fuel pump, or clogged fuel filters.
Yamaha has recently released a service bulletin recommending the installation of a 10 micron filter/water separator to combat the possible effects of ethanol in the blended fuel.
Guess we're all gonna have to do it.
Good luck [img]smile.gif[/img] ,
Ken K

[James]

Guys, thanks for the reply. Im gonna try it one more time. If it gets on plane and then after running for awhile again, I was also leaning towards a thermal issue. Cant imagine the new thermostats and the impeller not taking care of that. Back to the drawing board. Ill keep you posted.

[Ken]

James,
By "thermal", I meant something heating up and expanding - not motor overheating from lack of cooling water from the water pump.
Take a look at the throttle linkage again. Make sure the carbs are opening up all the way BEFORE the remote throttle handle maxes out. Maybe the throttle linkage is at its max when cold, and then with everything heated up, not quite getting there. Its a possibility.
Also, check the choke butterfly valves - make sure they are perfectly flat when choke is not engaged. Make sure linkage is free and not binding at all.
Good luck, and let us know how you come out [img]smile.gif[/img] ,
Ken K

[James]

Ken, thanks. Now that you mention it, I wonder if the control cables or linkage have stretched and need some adjustment...
Ill check that out too. I bet they are the original throttle cables. Should I try and lube them then adjust?

[Ken]

James,
Try disconnecting the throttle/shift cables at the motor, and then operate the remote. If you feel a lot of resistance, then time to replace cables or lube the old ones.
Good luck [img]smile.gif[/img] ,
Ken K