I recently bought a 1995 Polaris 400l 2x4 brought it home cleaned it up, carb clean, new air filter, fuel ect,, now I'm a small engine mechanic so I know my way around these but now that I have cleaned carb ect when you rev it up where ever you rev to it stays there for a good 20-60 seconds and I can't figure out why, and before you ask yes the slide is going back down all the way and also it gets quite hot so it starts "dieseling" and I can not shut it off so when it hangs up wide open going down the road is not a fun experience lol any help would be greatly appreciated!

 

No easy answers here, but I have just completed a quad that the previous person who worked on it really effed-up the throttle linkage, causing it to hang up and not close completely. When turning the handlebar, it would sometimes pull on the cable and cause it to really race.

In your situation, it sounds like it may be revving lean. Does the exhaust header get dull red?

Interesting problem.

 

Either running lean on jetting,or has an air leak from the crank seal behind the drive clutch, sucking air from a head or base gasket,intake manifold leak,etc. Also bleed the 10mm screw on top of the head that's close to the temp sensor. Could have trapped air that can cause them to run hot before the fan kicks on.Stock main jet is a 200,30 on the pilot jet.A leak down test can help along with some soapy water to see if it's around the base gasket,intake or crank case leaking itself. On the crank seal,you have to pull the clutch cover and spray behind the drive clutch to see if the crank seal is leaking while under pressure.Or simply pull the clutch and replace the seal anyway.

 

I tore into the bike some more and found a massive hole in the crank case at the back of the engine where it has previously blew up, it has since been patched and now the patch is leaking and sucking in air causing it to stay reved up when giving it throttle, any suggestions for something to seal the block back up ? I do not have access to an aluminum welder either :/

 

Best way is TIG welding, but I have used aluminum MIG welding with 4043 wire successfully. Epoxy can work, too, but the best way will be to take it apart. For TIG, I have a pal do it, and I am happy with the results.

Glad you found the problem.

 

Usually this happens when they break piston skirts. Always seems to happen under the intake manifold area.Only remember one I had that shattered the front of the cases.Used 350/400 cases are starting to become scarce on ebay,plus most people are selling them by the left or right hand side.Hope you can make this one work.

 

Bb