I am new here and just bought a 2006 Sportsman 450 AWD Browning Edition. I have owned it now for 2 weeks, I first rode it and it sputtered and ran very sloppy out of the hole, very dissapointed! So I went thru the carb, as I am very familiar with the mukuni carbs, surprisingly it was actually very clean, but I wasted a full can of carb cleaner on it blowing the clearner through every jet, port, opening, cleaning the slide, and diaphram. Put it back on and it ran better, but still from time to time had a problem getting out of the hole from a dead stop. Also I found that the previous owner had taken the air filter out of the airbox for what ever reason?? But I put a new air filter in it. It would run ok but near like I figured it would or should still stumbling almost like it is loading up/running rich on fuel from a dead stop or under a hard load. Side note: I had checked all the fluids, oil, spark plug, etc...obh yeah and I added a bout 8oz of Chem-tool carburetor cleaner to a fuel tank of fuel, just in case.

None the less it was running halfway decent so we decided to take a 4-wheeling trip, my fiancee rode it, and she said tat it ran pretty good, we stopped and took breaks from riding and it would start right back up just fine no problems...we finished our day about 7-8 hrs ride and parked for the night. Got back up the next morning and went to try and start it up again and nothing other than a couple of backfires out the exhaust.

Got home and went through some minor diagnostics: we have good spark for as long as you turn the starter over, we have fuel, have good compression...shot some ether to the intake and nothing it is still not starting, again some backfires but still nothing.

I am very mechanically inclined worked on 600 and 750cc 4-stroke motorcycle engines I assume the single cylinder engins are pretty much the same, but I have read stuff about the flywheel key being sheered, cracked carb intake, the pick up coil on the crank shaft, the ATC??? does anyone have any ideas where I should start with tracking down the problem. It ran just fine fir over 6hrs and now it just wont start??? Please help...

 

Check the flywheel key first,just remove the recoil, remove flywheel nut and you can tell if the key has still lined up on the flywheel slot(only had a few 500 engines shear a key,but 450 right in there!). Also I believe this model was on the ecm recall list,could have something to do with your problem,even if its had a replacement!(I've done a couple more than once) Just my Ain't a big fan of Chem tool in the gas,too strong on plastic and rubber parts if too much used! Use marine Stabil,removes water and preserves octane much better. Plus welcome to the forum! OPT

 

ok thanks OPT, I wont be able to get to the 4wheeler till tomorrow night, but I will start there. I used the Chem-Tool for a couple of reasons, I new it would give the fuel tank, carb, piston, valves a good cleaning. I did mix it a little hot, buton the next tank of fuel I will not add anything to it.

When you say "recoil" you are talking about what the pull rope winds up in when you pull it out to start it using the pull start right?

I will keep you posted on my findings from tomorrow night as well.

 

Yes recoil housing,then just remove the flywheel nut and you can see if the key is still lined up in the slot in the flywheel or has sheared and flywheel has moved a little. Only had this problem seems like on a few Sportsman 500s. OPT

 

I pulled the recoil housing and the nut, the flywheel key looked like it was all in place and not sheered. I did try to pull the flywheel off, but the gear/flywheel puller that I had didnt have enough strength to pull it off. I used a deadblow hammer to beat on it trying to get i to break loose but after a hour o trying I gave up and put it back together. I went ahead and looked at the ATC to make sure nothing was out of adjustment there, all looked good. I turned the key and had to crank on it for a couple of times but it finally busted off ad ran??? I dont know that I did anything??? But its running now. It is still running sloppy, so I moved the carb and set the slide neddle 2 notches deeper, wondering if out of the hole that is is flooding out causing it to spit and sputter, but when I put it all back together and took it for a test ride it was worse and had absolutly no top end. It is for sure starving for fuel now. I think I am goin o have to go the other way with the slide needle.

OPT do you have any ideas? Also how do you take the choke cable out of the carb housing? The area is too tight to get an end wrench on it?

 

Put the needle back on the 3rd position from the top! If you have to keep moving the needle,then something else is wrong! Drain the old fuel with the Chem-tool in it (how old is the fuel!!) could be part of the problem.Leave the choke assembly alone as long as it is moving(you should be able to tell when you remove the carb slide for the needle change and look through the top of the carb!) Also I would replace the needle and seat and check that float is parallel with carb body when upside down. Also check the fuel tank vent to see if its kinked.Plus have you checked the valve clearance (.006 intake and exhaust) Anytime you buy a used machine I would change the oil,filter,plug,and check/replace the air filter(you never know when it was changed!) OPT

 

The fuel is fresh, premium grade. I dont know if I had said in my original posting, but I had completely went through the carb when I bought the unit, as it was running sloppy then (stumbling off the bottom end/out of the hole when under a load), so I went to the local Polaris dealer and bought what I thought was a 450 carb rebuild kit, got it home pulled te carb off and started cleaning it out, and went to replace the jets and I noticed that none of the jet numbers matched, I looked a littl closer atthe rebuild kit package and saw where it said it was for a 700 sportsman, so I just sprayed a full can of carb cleaner through all of the original jets and through as all openings I coul find on the carb. I didnt not check the float level, but I did pull the original needle and seat out compared it to the needle and seat that was in 700 carb kit I bought, they appeared to be the same size and had the same markings, so I put the new needle and seat in. Do you think this could be causing some of the problem I am having now?

I will go ahead and move the slide needle back to the 3rd notch from the top as you reccomended, as well as I will go ahead and drain the tank completely, check all of the fuel lines, vent lines, change oil, spark plug, and filters (minus the air cleaner as I had already bought one and put it in).

I had not checked the valve clearance yet as I really feel that this is a fuel related issue? But if you feel like I should do this while I am in the process of doing everything else...??

Again thank you OPT for all of your guidance, and as soon as I can get the time to wrk on it I will let you know how the changes affect the performance.

 

Needle and seats are the same for the 450 and all the carb model 700s (#3131360) so that shouldn't be a problem! If it was mine I would do what you are doing(back to front,side to side!), as its a used machine! Even though valve clearance is usually not a problem on the 450 and 500s,(they probably will be at .006 intake and exhaust when you check em) I would still check em and everything else,BUT that's just me!! That way you can do a process of elimination as to what the problem may or may not be and have peace of mind as far as WHAT has been done and WHEN! Maybe I'm a little paranoid over used machines,but after what I've seen over all most 23 years is the reason why! The jets are no problem,as I usually just cleaned em myself and reused em(only replaced em when they were too trashed up!) Good luck and keep us updated! OPT

 

what is your plug gapped at? My 400 2 stroke did this. I know theyre two different animals but just throwing an idea out there

 

how many miles are on machine? maybe sercondary clutch button worn , alot of people think its a carb problem when its the buttons making cluch not shift right