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A low port 750 can pull a higher pitched impeller. The higher port cylinders may really struggle to get on the pipe with the same prop. You often have to see how quickly it responds and then do some pump load tuning to make it right. In your case it’s turning up enough rpm but not biting any...

Great find! Its old so a complete disassembly/inspection/reseal should be done before you put back into service. They are very easy to burn up unless everything is just right.

Most of the power is coming from the pipe rather than the engine once the ports are high. Just be sure about your fuel and tell the engine builder exactly how you ride. If he cares he may even listen to you.

Which “good fuel” option is best for “bad fuel”, is that the question? I doubt that they are going to send you a top end with very low compression.

What fuel are you using and how long are you going to be at full throttle? Larger bores need higher octane, especially over long full power periods.

Any steeply pitched impeller will boil water at low inlet pressures. They can work okay on a heavy V-bottom sitdown once it gets moving. They will barely work on a standup at top speed. Some of the local riders were trying to run FX1s with piped 760s. They would all just redline at slow speeds...

The stock FX1 pump doesn’t match the torque rpm range of Yamaha 650-760 engines. It basically is a 440 pump. It would work better with a 17 degree impeller spinning over 8000 rpm.

The only way the small pump can work better is by lowering the pitch and turning a lot more rpm. A Kawasaki 650 pump with a 900zxi shaft will work much better with any 650-760 engine.

Your high rpm ignition timing would be the limiting factor. It would run forever IF the timing was pulled back enough. All of our rules of thumb are based around the stock fixed ignition timing. At 23 degrees the engine would be detonating at full rpm and would melt down in a few seconds. If...

Yamaha cylinders have some high stress areas so they must be cast perfectly in order to have much fatigue life. The combination of poor design and low build quality cause premature failures. They could never be certified for aviation use.

Leave that head on there as long as it seals good. Get the pipe and concentrate on getting the pump load right. You need to see 7000 rpm or more. Its really amazing how much response and acceleration you can gain from boring the nozzle and just slightly bending impeller blades. Most riders get...

A lot of compression can be used as long as the fuel mixture is rich of peak power and/or if long full throttle runs are avoided.. A 760 with stock timing can be easily melted at 180psi on pump gas.

Air leaks wont affect a PWC as badly as they do a motorcycle. Jetskis are always under an increasing load from idle to full rpm and the rpm drops instantly when the throttle is closed. Air leaks cause motorcycles to burn a piston (mostly) while at part power and while coasting. Try tying the...

Your engine can create only around 6psi in its crankcase. The only way it can blow out a seal is by having a lot of liquid inside or by having a loose grip between the seal and crankcase. Its unlikely liquid caused the problem since enough of it would get blown into the cylinder and cause a...

I like to run 2.0N/S on single carb intakes just because a drop in fuel pressure will make a 1.5 act as the jet, which is smaller than the restrictions up stream.. In theory having a constant 5psi at the N/S would allow for a much smaller one.

Leave it stock until you master carb and pump tuning. Then raise the compression a little. The only difference is low end throttle response.

Never looked at a facebook group. I imagine there must be thousands of people asking "What jets do I use".

Did you affirm that the carb setting was rich of peak power on the initial setup? If not you set yourself up for failure. At least you found the meltdown setting of your setup, which has some value.

He may not be able to get an XFR to plane without a 2 foot pole. A little hard on the back for chasing boats around. Depending on his size that is.

"Spoon hulls" , is that a technical term???