Polaris ATV Forum banner
1 - 11 of 11 Posts

·
Registered
Joined
·
31 Posts
Discussion Starter · #1 ·
Need some help troubleshooting...It will start and idle. When you give it throttle, it cuts out, sputters, and wants to die. I I have been through the carb and it is clean and clear (all jets are stock and everything is set back to original settings). The exhaust is not plugged. The intake and air filter are in good shape. Spark plug is new. Using the choke doesn't seem to make a difference. The plug looks lean, very dry and hardly any trace of burning anything. If I cover the air box with a piece of plastic, it seems to run a bit better. The top end has good compression. I have not ran a leak down test yet. I turned the fuel screw out a couple of turns and that didn't appear to make it run any better. A

Any help would be appreciated.
 

·
Registered
Joined
·
261 Posts
Also check the rubber boot going into the carb and the one going out of carb into engine for splits or cracks.
 

·
Registered
Joined
·
31 Posts
Discussion Starter · #4 ·
Yes, stock air filter. I will double-check the intake boots. I forgot to mention that the fuel pump will hold pressure on the diaphragm (per the manual) and it is pumping a healthy amount of fuel to the carb (I can see that the fuel filter is full of fuel). I am thinking about going through the carb for a second time. I just can't believe that it is anything else, like say electrical. I did check the valves and they are pretty loose, as far as .014" whereas they should be .006". I don't see where loose valve clearance would cause the motor to run like this though.
 

·
Registered
Joined
·
261 Posts
If you don't find an air leak I would say carb for sure. Before you take the carb off put some Seafoam in the gas tank 1 to 2 oz per gallon of fuel in your tank. Let it idle for about 10 min. To get it thru the float bowl and into the carb. Also put some into a spray bottle an in a well ventilated area take off air filter and spray it into intake while running. Slow at first then really spray it in and the engine should choke till it stops. Let it sit for 30 min put the air filter back on and fire it up. Should smoke for a bit then run much better.
 

·
Moderator
Joined
·
12,816 Posts
I'm with Russ on the valves. If they were that loose you may have an exhaust lobe worn. You can check the carb boot and intake by letting it idle and spray around it with carb cleaner or starting fluid to see if idle changes. You might also try disconnecting the black wire from the Rev limiter (#30) to disable it. They can cause some weird problems sometimes.

 

·
Registered
Joined
·
31 Posts
Discussion Starter · #8 ·
I pulled the carb off and cleaned it again. It is perfect. The air boots are in good shape also. I adjusted the valves. The valve train does not have a lot of visual wear, but I didn't pull it apart and measure. None of this helped. It still pops, backfires, etc. when I try to rev it. It starts and idles really good. When you start giving it throttle, the trouble begins, but it never dies. I pushed the reverse over-ride and it did not help. Once it is warmed up, it will not run with the choke on. I put a battery charger on it just to see if I had low voltage causing issues, but it still runs like crap with a charger on it. I will try the rev limiter next...
 

·
Registered
Joined
·
31 Posts
Discussion Starter · #9 ·
I tried the rev limiter (black wire), no change. I pulled the plug and it is now showing a rich condition, rather than the previous lean condition. I checked out the exhaust and it is not plugged up. I checked out the cam chain tensioner and cam timing all is good. I decided to leak down test the top end. I am losing 10% to leakage. I have not been able to 100% verify where it is going. I do not detect air coming out of the intake or exhaust ports. I am assuming that it is leaking past the rings and going down into the bottom end.
 

·
Registered
Joined
·
30 Posts
If you find out what is wrong with yours you'll discover what is wrong with the '97 500 Sportsman I've given up on. I went through everything like you,even took the cam out and measured the lobes, reset valve clearances, went through the carb several times, checked all hoses and replaced many of them, nothing. I took the pump apart twice cleaned and looked for any issues, same with the diaphragm in the carb. It pops right off and idles perfect, give it gas and the fireworks begin. If I cup my hand over the intake(air filter off) and allow it to barely get enough air for it to run, it will rev right up wide open. But try to get any revs without snuffing off the air intake, forget it.
I've rebuilt dozens of Japanese bikes/quads and modded just as many in every way, shape, and form, I have never had a motor refuse to work. I shoved it out back and walked away.

My theory is the p.o.s. fuel pump doesn't work right, but the thing isn't worth buying parts just to see if it fixes it, at least if it was electric you could run it to test for flow and pressure. I was thinking of just bypassing it like a normal bike does and run the line from the tank to the carb, then plugging the vacuum outlet off to see if it works then, but for now it was best to just forget about the whole thing. Probably just sell it as is.
 

·
Registered
Joined
·
31 Posts
Discussion Starter · #11 · (Edited)
Worn Exhaust Cam

I finally decided to just start taking things apart...As I began to disassemble the rocker shaft, I noticed that the shaft had shifted to the right towards the cam sprocket. It had shifted far enough that it was rubbing on the back of the cam sprocket. This means that the left side of the rocker shaft was barely supported and it showed excessive wear on the shaft and bore. With the rocker assembly removed, I could see the exhaust lobe on the cam. It was worn down to nothing. See attached pic.
 

Attachments

1 - 11 of 11 Posts
Top