2000 90HP Yamaha Bogs Down

[stpetesal]

I have a 2000 90HP Yamaha, engine will intermittently bog down while I am at full throttle, I power down somewhat and after doing this a couple of times no problem, will run for hour and not do it again, but it happens about half the time I go out. I have good gas, replaced water separator, checked fuel filter (it is clean) can’t find any leak in fuel line, I originally thought it was only after hitting a small wave but it did it on a very flat day. I have not pulled carbs yet but was wondering if anyone else as this problem. Thanks for any information.

[99yam40]

monitor fuel pressure/vacuum, spark, and timing to see if something is changing when problem shows up.

When was last fuel pump change?

May try draining carb bowls to see if you have trash or water floating around in them

[stpetesal]

Already drained carbs, but not sure how long ago fuel pump was changed, When problem shows up I am under full throttle, cant look a spark and timing while driving, and only dose it under a load.

[99yam40]

timing light will show if spark it dropping at any RPM and also show if timing is in spec, just need some one to help or use a Yamaha test prop with boat strapped to trailer at ramp

[pappastratos]

Sounds like it is running out of gas, could be air leak around primer bulb, obstruction in the fuel line,filter, or pick-up. Or could be the fuel pump getting weak. Pump can not keep carbs filled up at high speed. had a yamaha guy tell me to replace the fuel pump every 10 years or so.

[axolotl98]

Leaning out...
Replace fuel pump membranes and clean carbs.
file papastrato, eisai apo US meria?

[stpetesal]

All Fixed, Bad Anti Syphon

I fist put 6 gallon external tank on and had no trbl (enging fine)then after checking, fuel filer, draing tank, changing all gas lines, ball pump and connection to engine, moving center consel to cut small opeining and put bigger hatch in so I could work on tank, I found a BAD FRICKING ANTI-SYPHON VALVE, A co worker spent hundreds of dollars a the dealer and trouble never went away, and the owner of Cost Marine in Maderia Beach FL told him to remove his anti - syphon valve, and his trouble was fixed. I found out the hard way, but at least it is fixed and only cost me $35.00, for new hatch, 25.00 for gas line and some 5200

Seachoice Anti-Syphon Valve 1/4Nptx3/8 SCP-20991, Gasoline-Diesel Fuel Filters

[boscoe99]

The sad part is that anti-siphon valves are not even required. They do nothing but cause problems. Why in the hell they are installed in the first place is the mystery.

[Marc Kruse]

What I was told it is there so if you boat sinks it won't let the fuel leak out. GC rules
I know they can cause problems and most people just knock the ball out at the first sign of a fuel issue.