Hi, I have a 1997 Polaris Sportsman I bought about 2 years ago and I have not had nothing but issues with it. When it runs right it runs good, that's not very often. Engine will start up and idle perfect as you give it gas it will start to throttle up and when it reaches half throttle rpm it stays there. The throttle cable running the butterfly is working fine and opening all the way. I removed the air box to take the carb off but before I removed the carb I started it to look and I found that the problem is the the vacuum slide in carb is only going half way up. I checked the slide it moves freely all the way up like it should with my finger but in the quad its only going half throttle. I've cleaned and checked carb seems ok the diaphragm look ok with no holes that I can see. Is it not creating enough vacuum to move the slide all the way up?? Has anyone ever seen this issue or have any ideas on what it could be???
Any help is GREATLY APPRECIATED.

 

Have had springs under cap become distorted,trying to lock up slide. Also check for excessive wear on slide edges and inside wear on plastic slide guide. ALSO have you checked valve clearance? Needs vacuum to work properly,tight valves could contribute also. Is slide needle and locking plastic pieces properly in place,can needle move up and down under pressure from spring?