1987 Yamaha ProV150hp

[Leonard Ray]

I have a 87 ProV 150 that I have been working on. It starts great runs good gets up on the water good for about 100 yards at 5500 rpms and then starts going and down in rpms and then will not turn over 4200 rpms. I have clean and rebuilt and the carbs ,new fuel pumps and fuel lines. You can let it set for a day and it does the same thing.Any ideas what I need to check?
Thanks

 

[99yam40]

monitor the fuel pressure and vacuum while problem shows up

You can also use a clear tube to look for air being sucked into the system

Look in the frequently asked question section of the forum for a write up on testing fuel system

Also check fuel pump to make sure it is not leaking and dumping fuel into crank case

 

[Leonard Ray]

When I pump the ball up i see no leaks but one min. latter there is no fuel in it. All the fuel has runs back down to the tank.

 

[Leonard Ray]

I replaced all the fuel lines and put new clamps a all connections. It helped some but still will not turn over 5000 rpms. Where would it be losing vac. at?

 

[99yam40]

have you tested anything ?

 

[Leonard Ray]

Not sure how to. I have tested it spraying starting fluid around carbs . But only does it under a load.

 

[99yam40]

did you look like I said in the frequently asked question section for fuel system testing?

 

[Leonard Ray]

Got it will try this thanks!

 

[Leonard Ray]

Can any one tell me what the float height and float drop is on this engine? And what do the idle mixture screws set on?
Thanks