130hp yamaha, 2002 surges at WOT once warm

[anzomcik]

Motor starts fines and runs smooth. After couple miles cruising or 20 minutes putting around the motor develops a surging starting around 5000rpm. Onlty when warm. Carbs were rebuilt last september, fresh fuel with treatments.

It will go hard until 5000-5300 rpm then lose power, rpm drop to 4600+- rpm then get going about until hitting 5-5300k. maybe 1-2 second pulse.

Back off throttle to a cruising 3-4k rpm and runs fine, back off to idle runs fine and smooth. Get on plane nice, but surges start around the 5k mark. No surges happen when the motor is "cold" only once the motor has been running for say 20 minutes.

Any insite?

 

[rejesterd]

Pump the fuel bulb right before you throttle up to WOT. When it surges, check the fuel bulb to make sure it's still stiff. If it's soft, then it's a leak in the line somewhere. If it's still stiff, then it could be a clogged fuel filter or the fuel pump is overheating and needs to be checked out or replaced. This is assuming it's not related to the carbs or bad fuel.

 

[AL311]

Motor starts fines and runs smooth. After couple miles cruising or 20 minutes putting around the motor develops a surging starting around 5000rpm. Onlty when warm. Carbs were rebuilt last september, fresh fuel with treatments.

It will go hard until 5000-5300 rpm then lose power, rpm drop to 4600+- rpm then get going about until hitting 5-5300k. maybe 1-2 second pulse.

Back off throttle to a cruising 3-4k rpm and runs fine, back off to idle runs fine and smooth. Get on plane nice, but surges start around the 5k mark. No surges happen when the motor is "cold" only once the motor has been running for say 20 minutes.

Any insite?

Have you tried new spark plugs?

 

[tommarvin]

Carbs were rebuilt by who, did they rebuild the carbs like all the you tube videos?correctly remove the welch plug if you have it
the motor will go to 5000-5300 rpm then lose power ,our overrev starts stopping spark at 6300. so below overev.
No surging when the motor is cold, I have read this post more than any other post for two strokes, This is whats goin on.
" When old/failing ignition parts get hot they dont work until; it/they cool down, your motor always starts when hot so its the carbs,The motor is starved for gas or she would turn wide open throttle, and than start stopping sparking to spark plug/s.
This is a tough post,but at the end of the day its always carbs.
If your boating budget will buy a used four stroke EFI you should

 

[robert graham]

Probably a fuel delivery or fuel venting issue....is fuel cap vent open?

 

[anzomcik]

I should add when "cold" (i give it a minute to "warm up") i can run 5800-6000 rpm with speeds about 45-46 mph.

I pulled the coils hoping to find a crack, they are clean. I checked them with an multimeter (isnt 100% reliable test procedure) but all tested fine and equal to each other.

carbs were rebuilt last september. I pulled the bowl plug and fuel came out clean, no sediment or anything out of ordinary.

Fuel water separator is brand new, maybe a 2 gallons of fuel ran through it

Spark plugs are brand new less than an hour old of use.
Venting is fine,

 

[rejesterd]

Testing the coils with a multimeter and replacing the plugs doesn't confirm good spark. You need a spark tester and perform the test on each plug wire (and test it immediately after the issue occurs). But I agree with tommarvin in that you would have trouble restarting the engine when it's hot if the issue had to do with ignition.

Also, the fuel/water separator filter is different from the fuel filter on the engine itself. You need to check both.

Also, removing the bowl is just part of rebuilding the carbs. There are other parts to clean (and possibly replace).

It definitely seems like a fuel delivery issue, which means the carbs still aren't right, there's a clog in the fuel filter or water separator filter, there's a leak in the fuel line somewhere, or the fuel pump is faulty.

It might also be a small air leak in the intake manifold, but since you never stall out when throttling down, I doubt it's that.