Motor is surging and not maxing out.

[pamunkey]

Yamaha 150 is surging at low rpm and is running at 4600 at wot. instead of 5000. carbs were rebuilt last year and have only run 2 tanks thru it since. plugs and filters changed with no results. Whats my options w/out rebuilding carbs again if possible and is this something resulting from 10% ethanol in the fuel.

 

[robert graham]

Re: Motor is surging and not maxing out.

sounds like a fuel pump/pressure/delivery problem. check fuel pumps.

 

[jbelcner]

Re: Motor is surging and not maxing out.

Are you getting spark from all plugs? This being a 150 hp you will have 6 to check and should have one coil on each plug (depending on the age of the motor). I would test to ensure that you are getting fire on all 6 cyl.

The bad news could be a bad cyl all together. Have you put a compression test on these yet? Not sure what the compression should be, but I think it is about 120 PSI. You will have to consult a maunual or a mechanic for the specifics.

Hope this helps.

JB

 

[pamunkey]

Re: Motor is surging and not maxing out.

Thanks for the input fellas. I'm going to start the troubleshooting this week and hopefully it's a simple fix.