Need Help with Yamaha 150 4-stroke- loss of RPM/ Vibration

[woowoowoo]

2005 Yamaha 150 4-stroke. Here is the deal, it ran great all summer, My gas mileage was getting worse so we changed to a 19 prop, and we had a 17. When I changed props, we lost 1200 RPM. At WOT we were hitting 5000 RPM. Since then, I went back to the 17 prop, and now the motor goes to 5200 rpm and then the rpms begin to fall down between 4000 and 3000 RPM. Also, we have a vibration in the motor. Any Ideas?

 

[BaileysBoat]

Re: Need Help with Yamaha 150 4-stroke- loss of RPM/ Vibration

Stay with the 17p until you correct the performance issue.

Could the vibration be an engine miss?

How many hours and have you checked the basics, compression and spark.

What do the plugs look like?

Have you taken a fuel sample from the VST?

Do you have a 10 micron filter installed?

let us know.

 

[woowoowoo]

Re: Need Help with Yamaha 150 4-stroke- loss of RPM/ Vibration

Hey there,
The plugs we not to worn but could be replaced. There is miss. Not sure. I had a 10 micro filter on it and when I lost rpms I took it off thinking that it might have a restriction. Problem has gotton worse.