Since this site was still in my list of "favorites" but transferred from a different computer, I was a former member here some years back but "dormant" due to 2 rotator cuff operations and other wonderful medical issues. More to the point, my 2005 Sportsman 500HO has been garaged most of the winter but I went to use it the other day and after warmup, with the choke in, the idle would either be normal (1200RPM) or be at 2000-2400-2800RPM. Same thing after a test drive various times letting off the throttle. Odd thing is, after maybe 15 seconds at 2300+/- it would slowly go back down to 1200 or die. The throttle shaft, cable guide and cable operate smooth as silk, no sign of hanging up, the cable guide, spring, etc, inside the housing are like new. In fact, with the engine off you can see and hear the cable guide contact the idle speed screw when working the throttle back and forth. I pulled the carb, like new inside, no foreign material, blew out all the passages, my shop manual calls for 2 turns on the idle pilot jet, it was 1 1/4 so I reset it at 1 3/4 since I'm at 5000ft. I DID find a slight crud buildup on the diaphragm slide which I cleaned off although it showed no sign of hanging up when worked manually. Got it back together yesterday, starts quickly, runs up and down the road normally with normal power which it did before, but I've still got the exact same erratic high idle condition. If it means anything, this machine's only got 1975 miles on it and never been in water. Any help would be GREATLY appreciated, I'm tearing out what little hair I've got left.

 

Gas fresh or preserved with a good stabilizer? Did you spray a little carb cleaner or wd 40 around the intake to see if idle changes? Not a fan of pulling a carb and just trying to clean one. At the very least it would get a new needle and seat or a Shindy carb kit which is cheaper and good Japanese quality parts.Shindy Carburetor Kit Polaris Scrambler 500 2003 2005 Sportsman 500 03 05 Carb | eBay Plus do you still have the spring on the bottom of the carb that holds the idle adjuster? Often times these break and the adjuster just lays on top of the starter. Vibrations will cause the idle adjuster to move around changing idle speed.This is a tough carb to get right also on float height setting. Manual doesn't really go into detail on the carb,but if not set correctly it can play the devil with the way one runs and idles.Here's a good post with pics on the BST40 carb used on a Ktm and how to set set the float height correctly.The BST-40 Bible | Adventure Rider Sorry about the rotator cuff surgeries. Wifes' in the second week of therapy on her second one also,not a happy time around here.

 

Thank you for the response, OPT, it is much appreciated. The gas is fairly fresh, maybe 4 months old. And I did not do the carb cleaner trick, but I will, and the idle adjuster retainer spring is still on the carb bottom like it should be. I definitely bookmarked the carb OH link, as you said, the factory manual isn't too wonderful regarding the carb section. I should qualify the 4 month old gas answer. There's a good chance some gas in the tank was older than that, I basically didn't go on any long rides all last summer. I just fired it up maybe 10-20 minutes a few times to turn on the headgate when irrigating my pasture. If you think stale gas could be the problem, I'll sure drain it and give that a try if that would be your first step. It's definitely intermittent, I went out and started it for less than 5 minutes today and after a short warmup it idled right at 1200. I sure don't feel like pulling the carb once again and still find no definite problem, everything internally was spotless and appeared in A-1 shape, no wear on the jet needle, etc. I'm a retired 30+ year heavy truck/diesel mechanic but that definitely does not qualify me as an expert on small engine carbs (or possibly stale gas). Thanks again and I hope your wife heals up quick-like.

 

Fresh gas could possibly do wonders on the way it idles. Easiest way for me to flush a tank was to stick a hose in the tank,stuff rags around it and pressurize the tank with an air nozzle. Makes short work of tank flushing. Had to do that may times on water craft with water contaminated fuel.The only way you can get gas out of those things without removing tanks or just gravity draining and mopping out tanks.

 

Thanks to your help, that's the route I'm going to go after you got me rethinking the situation. Bad gas makes the most sense. It had been running perfectly when I parked it in the garage and the only thing that's changed is the quality of the fuel. I didn't find the float to be hanging up or leaking and filling with fuel like we'd find on some of the old Holly 4bls back in the stone ages. I've got an air compressor and everything I need other than hose which I'll pick up at Napa today or tomorrow. I've got a jug of Stabil but I didn't use any thinking I'd be using the machine enough where the fuel wouldn't go bad but things came up where I didn't---not real smart. I'll post back with what I find.

 

That's a great idea on the siphon method, easier than adapting my MityVac to a clear hose, or a mouthful of gas. The overnite temp dropped like a rock, it's in the 20's and snowing so I think this project's on hold for today.

 

Just make sure you have rags sealed good around the tank opening,low pressure on the air nozzle or you can have gas spray up in your face. Learned that real quick on the water craft. I always used a 3/4 or 1 inch diameter hose with the air nozzle right against it. You can drain 4 gallons of gas in no time. Even better after you drain it if you have a flexible grab it tool and some blue shop towels to mop up any residue from the bottom of the tank.Don't know how may gallons of gas we had to dump into our 300 gallon waste container like this over the years from water craft. I was almost temped to try to use some of it in my old truck.

 

I've dumped old stale gas in my truck before. Mixed with 30 gallons of good gas it doesn't make any difference in how it runs. I've dumped 2-stroke gas in at the end of weed whacking season too before I started using Sta-Bil. I could never tell the difference with that either but it was only part of a gallon.

 

Right, Jumbo, that's what I figured I'd do with it. Bad part is I topped the tank before I was aware of the problem, but no big deal. If I remember right they hold something like 4 gallons.

 

Thanks again, OP Tech, it appears my major problem was as you said, stale fuel. New fuel and a heavy dose of Stabil and it runs fine. However, when I siphoned the tank the clear plastic 1/2" hose I used was curled and stiff. I finally got it to the tank bottom but when I pulled it out it hung up then pulled free. Just then I thought, oh crap, I bet it hung up on the tank sender. It appears that's what happened because with a 1/2 full tank the gauge shows full. By looking in the manual, it appears pulling the tank or accessing the sender is going to be a real joy.