1996 250 Motor Hesitates

[Someday Came]

Hello,

I have a pair of 1996 Yamaha 250 Vx motors with carburetors and approximately 870 hours. One of the engines has difficulty operating between 1,700 rpms and 3,000 rpms--runs great below and above that range. We have performed the following work on the boat/motors:

Cleaned fuel tank, polished existing fuel
Replaced all fuel lines from tank to engines
Removed anti-siphon valve balls
Installed two new Racor fuel/water separators
Performed Yamaha 100 hour service on both engines
Cleaned all carburetors
Replaced all plugs
Installed new/rebuilt stator in problem engine

Basically if I go WOT out of the hole, the problem engine will die. If I gradually push the motors to WOT the problem engine will bog down and hesitate at 1,700 rpms until I surpass the throttle setting for 3,000 rpms at which point the engine will surge and run fine. The engine will never run in the problem range unless in neutral. Any help would be greatly appreciated.

[Tucker]

I've never heard of any success stories with polishing fuel. To eliminate that from the equation maybe run that engine on remote tank. This is assuming each engine is on it's own tank. Also, not sure where the pilot circuit is taken over by the main jet but my pilot circuits on my 200's were clogged and it was difficut to detect because they are so small.

[Someday Came]

Yes, we isolated the fuel supply during testing and it made no difference. Carbs have been cleaned twice now.

[jb123]

isolated with polished fuel ?
start with fresh NEW normal octane gas

when @ the problem range, feather choke, if it helps,clean carbs again

[Someday Came]

No, prior to polishing the fuel and cleaning the tanks, we ran the engines on separate 6-gallon tanks with ethanol free fuel. We thought the fuel might be bad or contaminated, but after cleaning the carbs and running the separate fuel tanks, the engine acted the same. Plus, the other engine works fine no matter what fuel runs through it.

[Someday Came]

No one has any ideas about this problem?

[Tucker]

Did you feather the choke like JB said?

[Someday Came]

Okay, found the problem. The Crank Position Sensor was loose and almost falling off. We put some new screws in it, secured it properly, and shazam! the engine started running properly. Thanks for all of the advice.

[Tucker]

How'd you know where to set it someday? There is adjustment to it right?