2003 GTI with 720 engine has no horse power

[sledman1]

I am looking for suggestions of things to check to determine what is causing a 2003 gti with the 720 engine to have about 1/2 the power it should. It starts up fine and idles perfectly. But when you give it the gas it accelerates very very slowly and never gets close to the top speed it should. There is no surging throughout the throttle range. Just a constant lack of hp at all speeds and throttle positions. It has been like this since the motor was rebuilt. Compression is good on both cylinders. The just pump spins freely and has a good impeller and wear ring. The only two things I can think of to check is the rotary valve timing and the ignition timing. I put the rotary valve on with the 360 degree wheel so I am having a hard time believing that I screwed that up but anything is possible. Does anyone has any other suggestions as to what could cause a 720 engine to start and idle fine but just not put out the hp it should. I have not looked at the carb because it has been rebuilt and the lack of power is constant from idle to WOT. Thank you in advance for any suggestions.

 

[Mekanix]

Flywheel stripped the woodruff key ? Causing retarded timing.

 

[sledman1]

Thanks, I will check for that.

 

[LouDoo]

You say good compression, I would go back and double check the compression. Are you certain it's not cavitation, you may want to look at the carbon seal, neoprene seal.

Lou

 

[sledman1]

No cavitation at all. I will double check the compression.

Thanks

 

[sledman1]

Compression is 130 psi both sides. I know that is a bit low but is it enough to make the jetski be very very slow on acceleration and be a good 15 + mph slow at the top end?

 

[LouDoo]

Well, I'm at a loss, I guess go back and take Stephen's suggestion and check the timing.

Lou

 

[Mekanix]

Its approaching the "time to think about rebuilding" if the compression is that low.
Although it could also be the rotary timing is too late. I've had one 717 engine that stripped the brass gear and then caught again. The engine hiccuped for a second but still ran and started with less power.
Also a lack of fuel will cause this, or worn outer crank seals.