96 GTi no top end

[JDCam]

Hey Guys,
My 96 GTi 717 was running very poorly a few weeks ago. Starts and idles fine, but if you take it past 1/4 throttle it bogs with short surges of power.
I took it into a shop to have it looked at. The mechanic concluded it was the pop-off valve and replaced the needle valve/seat.
It now runs nice and smooth, but doesn't go nearly as fast as it used to. Maybe 80%
Any idea what has happened and can I correct it myself?
I was going to take it back to the same shop but its a PIA. About 1.5 hrs away and 1-2 weeks backlog before they can look at it. Season is pretty much done now.

 

[etemplet]

Ride the ski and when it is limiting out pull the choke slightly. Did you replace the spark plugs?

 

[JDCam]

Plugs were not changed. but can do if needed.
I can try the choke this weekend. If it makes a difference what is this telling me needs to be done?

 

[etemplet]

Spark plugs can solve a lot of problems on those two strokes, no matter how good they look, swap them when you have problems. As for the pulling out of the choke, if performance improves you are not getting enough fuel. Pulling out the choke gives more fuel. Generally skis run worse when the choke is pulled out. That can either mean you are RICH or that fuel isn't the problem.

Check your compression.