1995 Yamaha 150 Problem

[robsco]

Running along at WOT and the motor just lost about 1/4 or so? of it's power. Every 6-10 seconds or so it would bump back up for a split second and then tone back down. It would do this at low speed too but not at idle. I also noticed when I tried to goose it onto the trailer it lacked the "goose" (so to speak).<br />Any ideas fellas?

 

[rodbolt]

Re: 1995 Yamaha 150 Problem

first place to look is fuel. what condition are the fuel pumps? condition of the filters? have you tested the plug cap resistance ?<br /> when was the last time the motor ran correctly?

 

[jasonalden]

Re: 1995 Yamaha 150 Problem

Robsco,<br /><br />I had similar loss of power issues in 2004 when I purchased the boat. See this thread:<br /> Lazy Cylinder On Yamaha 150 <br /><br />I have a 1997 150 2 stroke which has now failed with a blown rod bearing, and I strongly suspect that water was leaking into the cylinder over time, possibly by means of the cylinder head gasket..unsure.<br /><br />Don't let it go. Maybe Rodbolt or someone else can shed some light on how to check for leaking cylinder head gasket without pulling it.<br /><br />What I did was I hooked up the flush hose one day, and pulled the spark plugs. I looked inside the spark plug hole and found water misting sideways (however, AFTER my engine failed) - not much, but over time perhaps that contributed to my failure.<br />Here's what happened to mine. <br /><br />Good luck.

 

[robsco]

Re: 1995 Yamaha 150 Problem

Fuel pumps new in Aug '04<br />Filter pulled and looked good.<br />Don't know what plug cap is or it's resistance yet? Help?<br />Checked compression and all are above 100 with 105 being the highest.<br />I have a service manual but it does not cover my specific problem (of course).<br />Ran fine 2 days before.<br />Thanks for your replies and input

 

[Ray Neudecker]

Re: 1995 Yamaha 150 Problem

The compression test indicates the head gasket is good. Everything points to a fuel restriction. I would start with replacing the fuel filter. They always look good. Do not hold the engine open when it starts to act up. Very good way to break it.

 

[robsco]

Re: 1995 Yamaha 150 Problem

Spark plugs changed and old ones were pretty black in all cylinders. Electrical problem?

 

[Ray Neudecker]

Re: 1995 Yamaha 150 Problem

The basic checks are compression amd fire. Take a timing light or spark tester and check fire on all 6 cylinders. If it is there then you have a fuel restriction problem. Really don't know what else to tell you.