1997 SX150 runs bad only at high rpm

[Brian G.]

Hi guys. I have a 97 Saltwater Series 2 150hp. It starts great, idles great and runs great from 0 to 4200rpm. Over 4200 it cuts in and out and will only open up to 46-4700. When I back it back below 4200 it purrs like a kitten. I have done a quick visual inspection and everything seems to be tight and in place. Any ideas????

[lusky67]

I posted a similar problem a few days a go with my 1997 115 hp. My problem is exactly the same except it happens at 3500-3600 rpms. I pull back to 3000 rpms and it runs great. You can read some suggestions I got on 06/04/06. My mechanic is lost on what to do because nothing has worked. If you find out the problem please let me know. Thanks.

[Ken]

Brian,
Sounds like fuel starvation.
Get the boat up to speed at the point that the motor starts cutting out. Have someone check the fuel primer bulb - if it has collapsed, then there is a fuel restriction from there on back to the tank. Could be tank is not venting properly.
If the primer bulb has not collapsed, try squeezing it several times - if the motor rpm picks up, then you have a bad fuel pump.
If motor rpm does not pick up, then I would suspect clogged fuel filter, or clogged high speed jets.
If that motor was allowed to set up for more than a month w/o being run, then carbs could be clogged. Could try removing the high speed jets and squirting some Berryman's Chemtool into the orifices. If that does not help, then may need to remove carbs, teardown, clean, and install kit.
Also, if those plugs are more than a year old, replace them.
Good luck [img]smile.gif[/img] ,
Ken K

[hank]

I have a 1987 150 and I had a problem similar at RPM over 3500. My problem was bad heat sensors on the heads near the thermostats. A quick way to check this is to remove the cowling and then ramp up to high speed. If it does not cut in/out at high speed with cowling off, the problem is the sensors. They are not too expensive and only takes a few minutes to replace. I also replaced my primer bulb as a precaution. No problems since.

[kahoona]

I had the same problem with a Yama130. I just posted whe things that worked for me under the topic yamaha 130 loses power. After I did these things and applied the"Shock treatment" so beloved in these boards the moter ran like it never did before! Still does a year later.