2000 Yamaha ox66 surging at high speeds and fuel blowing out exhaust

I have a 2000 ox66 225 Vmax that is surging at high speeds and fuel blowing out exhaust at idle. It cuts in and out at full throttle then when I slow down you can see fuel blowing out the exhaust. Any ideas?

One of the mechanical fuel pumps is leaking fuel into the pulse port. Leaving all the fuel lines connected, Loosen the two 10mm bolts, wiggle the pump to loosen it from the block and squeeze the fuel ball. If fuel leaks out of the back of the pump, replace them.

I would also check compression and the ignition to make sure you are getting spark on all cylinders. A none firing cylinder (or low cyl pressure from bad rings) would just blow any unburnt fuel out the exhaust, as well as cause running issues.

Along with what Chris mentioned, if you can't pump the primer bulb up till it's hard (engine off of course), that's a sign that something isn't sealing i.e., floats sticking, fuel pump diaphram leaking by internally or the fuel pump leaking thru the diaphram and into the pulse port.

I had an old mercury do this one time and you could pump the primer bulb and hear fuel flowing into the engine. It was the fuel pump diaphram leaking into the pulse port and filling up the engine.

i checked and two of the mechanical fuel pumps were leaking. Went a head and replaced all three since i had it apart. went and did a test run yesterday and it was a lot better but still cutting out(surging) at lower speeds(3500 rpm's). Have to work until Thursday so I'll have to wait until then to do anymore troubleshooting. Want to say thanks for the help though.

Had a friend look at it and found that the port side head gasket was blown.

How did he determine that?

not sure i will have to ask him.