'99 2-stroke 150 // Surging/Hesitating

KDMatt

Seaman Apprentice
Joined
Aug 8, 2009
Messages
33
This is a carb'ed motor that was rebuilt/tuned a few years ago, and I'm having a recurring/stubborn surging and hesitation issue.

It started surging and hesitating a bit through the hole-shot at the end of last season, but smooths out on plane.

This season I replaced the fuel tank with a brand new moeller one, added a 10-micron screw-on fuel filter, new primer bulb, replaced both fuel pumps, and took apart and cleaned out the carburetors. I changed the plugs too. It ran great for a few hours -- thought I'd fixed the problem -- but then the issue returned.

I cleaned the carburetors again last week, but it's still doing it.

I'm up on vacation with my family right now, so the boat's in the water.

I have no trouble starting the motor, and while it stumbles a bit through the low RPM range, the hesitation only becomes an issue when I go from idle speed to open throttle... If I ease into the higher-RPM's it's not as noticeable.

I could use a few suggestions on where to turn next. Ignition? Would a vacuum leak cause issues like this? Incorrectly adjusted carbs? Could my floats be set wrong? There are some adjustment screws on the sides of the carbs -- do those ever need periodic tweaking?

I'm a car guy, and normally live in the realm of 4-stroke and EFI, so this is all a little foreign to me still. Any help anyone can offer is appreciated. Thank you!!

1999 Yamaha P150 TLRX
 
Last edited:

BrettNC

Petty Officer 1st Class
Joined
Feb 6, 2005
Messages
298
Sounds like a lean fuel mixture issue. You might be getting extra air into the motor somewhere. Check intake manifold gaskets, bypass cover gaskets, make sure the seal between the crankcase halves isn't leaking. Then check the reed valves. The top and bottom crankshaft seals might be leaking. Check condition of individual spark plugs for lean mixture.
 
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