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I have a 99 Yamaha 60hp outboard on my Maverick and have ben having issues at full throttle. The motor will bog down only at full throttle and make a kind of constant thumping sound but will not regain full power until I let it sit for a minute, then it runs fine again. Any ideas what causes this, motor runs great at any other speed...possibly jets in my carbs need cleaned out?
 

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I have a 99 Yamaha 60hp outboard on my Maverick and have ben having issues at full throttle. The motor will bog down only at full throttle and make a kind of constant thumping sound but will not regain full power until I let it sit for a minute, then it runs fine again. Any ideas what causes this, motor runs great at any other speed...possibly jets in my carbs need cleaned out?
When you say bog down, how much does it bog down?

Brett the rev limiter would immediately deactivate when the throttle is pulled back. Also rev limiter is more of a skip than bog down.

I would start by running the engine on a different fuel tank, line and primer bulb. If it runs fine on a different tank then you have a bad Primer bulb, A/S valve, line, W/S etc etc, problem is on the boat side.

Also easy check on the fuel pump pull the 2 bolts that hold the primer bulb to the engine block, (only those 2 screws, leave the other alone) squeeze the fuel primer bulb and if gas squirts out the back of the pump, R&R pump.
 

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Brett the rev limiter would immediately deactivate when the throttle is pulled back.
Also rev limiter is more of a skip than bog down.
That's what I get for trying to diagnose based on a written description.
The thumping made me think rev limiter. That's what mine felt like
when I spun a hub on an old 'rude 90. Of course the tach also indicated
an rpm overage occuring just as the limiter kicked in. :-[ ;D
 

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I replaced the anti-siphon valve and the boat ran great, no problems at full throttle. Didn't realize how fast the boat was until now. Thanks for the help.

Turned out the valve was basically stuck open and allowing air/gas through either side.
 

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I replaced the anti-siphon valve and the boat ran great, no problems at full throttle. Didn't realize how fast the boat was until now. Thanks for the help.

Turned out the valve was basically stuck open and allowing air/gas through either side.
Glad you got it figured out. Exactly what was wrong with mine.
 
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