Polaris Magnum 425 Camshaft Replacement / Timing engine 

Unfortunately China carbs never work on the Magnum 425. On the original carb take the 4 phillip screws off the top of the carb and make sure the rubber diaphragm boot is not torn.

And then while the machine is running make sure when the throttle is pushed look into the inlet of the carb and make sure the slide is rising up. Make sure it is not sticking

Also are you sure that is a Magnum 425 carb. Even though it is a Mikuni carb the needle is different then other Mikuni Polaris carbs that will bolt right on

The wrong main jet will cause this issue

They are just vent lines. They run under the gas tank and hook to nothing

It would not rev out completely. That is the same symptoms of a carb issue only though (which was confirmed not the issue before the cam was replaced). Make sure jets are not restricted in carb. Also air screw needs to be turned out 2 1/2 turns on the carb. A "China" carb will not work properly with the Magnum 425. It needs the factory carb for the Magnum 425. Other OEM carb will fit but are not "setup" the same. So, yes not revving out can be the camshaft also. Also when the cam lobes really get worn the machine will be hard starting and "pop" (backfire out the exhaust) when trying to start.

Thank you so much for the info!

Worn belt also will cause not revving out. Check carb and replace belt would do first and can be considered maintenance. The cam can be visible check just by removing valve cover and manual rotating engine

You were completely correct, the guy I bought this from put a new china carb on in. I installed the old nasty carb that it had originally and now it works like a charm- revs up no problem. The old carb needed me to place my hand over the intake for it to throttle up- obviously the new chinese carb has major vaccume issues

@@5347BBC Thanks! wouldve never thought to throw on the old carb. You saved my butt a chunk of cash