How can I tell if my muffler has gone bad?

Sometimes my 1999 Polaris Magnum 500 starts up immediately, usually when it's first thing in the morning. I know the fuel line is good - I cleaned the fuel pump and tested it. I replaced the gas lines with clear lines from the Dealership. Other times, like last night - it wouldn't start and I wore down the battery trying to get it fired up.

This morning, it started right up - but I had to press the throttle all the way in. It revved up good, but it would stall if I let the throttle go. I'm still trying to adjust the idle screw. Pilot screw is 2.5 turns out. I've cleaned the carb out 3 times now and rebuilt it with a rebuild kit from the Dealer.

There was a LOT of smoke at where the donuts connect the exhaust pipe - and the donuts are brand new. Last night I noticed fuel leaking out at those joints. I removed the large bolt on the muffler and started it back up again. The smoke was gone. When I turned off the machine, the hole was smoking and not the tailpipe.

There is exhaust at the tailpipe, but how do I know there is enough? I didn't see much come out the exhaust plug. I'm looking at the service manual that covers purging carbon from the system.

Note: the spark plug was fouled last night - wet and covered in carbon. I cleaned it the best I could and put it back in.

What I'm trying to figure out - why won't the machine stay running at idle? How can I rule out the muffler?

 

How about the slack at the thumb throttle? 1/8" only,any more than that the etc contacts can touch or can arc causing starting problems.Once adjusted,then the carb idle screw can be adjusted. What about the carb itself? Has it been cleaned and rebuilt? With fuel leaking,sounds like it's time. Checked the valve clearance along with the cam lobes? If you can feel exhaust out of the muffler,at least it's open. Using an impact and socket to remove the two clean out plugs and tapping on the muffler can help remove baked on carbon deposits,but the 4 strokes never had the problem of stopping up like the old 2 strokes had.

 

I've been watching the etc contacts, adjusting whenever I set the idle screw. The carb has been cleaned and rebuilt, although I'm no expert. There is no leaking out the overflow.

There is only one clean out plug that I can see on the muffler.

For the valve clearance along the cam lobes - I'm trying to figure out how to check that. Do I need to pull the entire engine out, or can I just remove the top end? From the service manual, it looks like I just need the seat, gas tank and plastics removed to get sufficient access.

 

This is the best thing you can buy..https://www.tradebit.com/filedetail....air-manual-all Plus here's the carb section from the manual you can download.https://www.google.com/url?sa=t&rct=...U2gGlaHJWSIlbA Again when you check the valves look at the exhaust cam lobe.Bad Cam Pic - ATVConnection.com ATV Enthusiast Community

 

Yes - that is the service manual I'm using. Thank you for confirming. I'll check the valves and exhaust cam lobe.

 

So while I check on those other things, back to my original question. How do you know when a muffler should be replaced?

 

Usually if it's rusted out. You can simply pull the springs off,loosen the mounting bolt and remove it.Then you can really look it over and check it out with an air gun,blow any crap out.You also can soak it in kerosene for a couple days.

 

I don't think it's the muffler then. I adjusted the valves and looked at the cam exhaust lobe, and have some questions. I'll start a new thread on that one.