175 Yamaha 2-stroke performance problems

[Jack Shea]

Have a 1997 Yamaha 175 2-stroke with 1000 hours running time. Carbs have been removed and rebuilt. End caps (all 6) have been renewed. New plugs. Timing has been confirmed on the mark. New Yamaha water separator filter assy installed. No indications of any sediment or water in fuel. Prior to all these changes, engine idled very rough, power loss and regain at 4000 rpm as if one or more cylinders cutting out/in. Recent repairs have engine running satisfactory at idle for docking/undocking and 1000 rpm in no wake zones. Powered up to 3900 rpm and trimmed out for max efficiency and ran that way for about 3 minutes when the rpms jumped to 4300 then back to 3900 right away. Engine did this couple of more times on a run of 2 miles. Also notice now that engine will only achieve 4600 rpm at max throttle when 5200 rpm had been achieved prior to this year. All these problems existed prior to first purchase of ethanol laced fuel.
Appreciate any help with this one.

[jb123]

if you have the average compression, bout 110-120, i would say tear and clean carbs again. you are having a hi end fuel delivery problem.
use a spray bottle of gar in each throat and listen for the rpm change, along with using your finger to choke each throat individually and also, pull each plug wire while running at about 1200 rpms.
it is also cheap enuf to replace ALL fuel lines and check every break for any air leaks and ensure you have no screen on pickup tube in tank. you can isolate it by using an aux tank.

[Ken]

Jack,
If your fuel pumps are at least five years old, I would replace them.
Good luck [img]smile.gif[/img] ,
Ken K