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Discussion Starter · #1 ·
My xc 500 with only 1600 miles runs like crap. I have cleaned the carbs twice, changed plugs numerous times, replaced all the fuel lines because the one in the tank had rotted and dropped the old fuel pickup screen. Fuel wise the only thing I'm waiting for is the rebuild kit to show up because one of the diaphragms was a little dented in. I drained all the old gas because the sled has been sitting for four years now. I was given this sled for free and I'm ready to throw it away. I have 125 psi at both cylinders, so I have ruled out any motor damage. I can get it to start fine and it runs low end ok but at 40 mph it craps the bed... any ideas?
 

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clean the power valves.....if it has them. betcha thats it!! use a soft scotchbrite pad and carb cleaner. BTW you will need new VES gaskets b4 u start to pull it apart
 

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Discussion Starter · #3 ·
That will be next, I'll try about anything. It is an otherwise flawless looking sled and I certainly couldn't beat the price. Do you know which side of the fuel pump the small diaphragms go on, I was stupid and marked everything else so I knew where things went but for some reason blew that important part of the process. thanks again

I am fairly mechanically inclined but not up to snuff with all the terms, when you say power valves? Where are they, between carb and cylinder...reed valves or am I on the wrong page?
 

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Power valves are on the exhaust side of the cylinders above the Y-pipe. If your sled is a plain XC, instead of an XCSP, it doesn't have them.

What does the sled do if you run it on a stand? Will it rev up to 7,900 RPM, or not? You could have something broken in the clutch. If you decide to throw it away, I'll take it.
 

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Discussion Starter · #5 ·
Oh it will rev way up, I rode it in my 3 acre lot pretty hard and things seemed fine. But I don't think I really got it passed 40mph at all til I tried it in an open field. That's when she kept crapping out and fouling plugs. Low end even sucked then. New plugs would help low end but hit 40 and foul again. Calling for that much gas and having that dipple in the pump diaphragm maybe causing the problem? What do you think? and yes it's a plain xc so no power valves huh. I don't know Polaris very well cause I grew up riding yamaduds.
 

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jeff.schulze said:
Oh it will rev way up, I rode it in my 3 acre lot pretty hard and things seemed fine. But I don't think I really got it passed 40mph at all til I tried it in an open field. That's when she kept crapping out and fouling plugs. Low end even sucked then. New plugs would help low end but hit 40 and foul again. Calling for that much gas and having that dipple in the pump diaphragm maybe causing the problem? What do you think? and yes it's a plain xc so no power valves huh. I don't know Polaris very well cause I grew up riding yamaduds.
Would you sell this machine?? What part of the world are you in?
 

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Discussion Starter · #8 ·
Sled is completely stock, it was giving the guy problems along with a 95 xlt touring 600 so he said if i went to wisconsin to pick them up I could have em. So...i took em. Also a 120 and a yamaha inviter 340. What a score, but I have been working late nights to get this 2000 running so I can go up North and everytime I think I found the problem I put things back together and things only get slightly better. I hope it's the fuel pump issue. I was silly enough to ignore which side of the fuel pump the two small diaphragms were on so anyone who has rebuilt one of these pentagon shaped walbro fuel pumps hopefully can help.
 

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You got all 4 of those for free!?!

You are getting to much fuel on the top end if your plugs are wet,the carb floats control the fuel amount after the pump so I would say it is not the fuel pump. Make sure you needle and seats are not sticky,if it sticks open it will pour extra fuel into the motor. Are both plugs wet or just 1?
 

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Discussion Starter · #10 ·
yep all for free. But they hadn't been ridden in forever so each has its own problems, although I have had all of them running. The 120 is a riot for my 4 and 5 year old kids. Both plugs are dark and damp but not really soaked when I pull them, the clutch side plug seems a bit darker though. I have no idea if the former owner messed with the two adjusting screws on the carbs. I know you can lean or rich it up a bit with those, I counted the turns when I took them out. They both turned out the same amount so I assumed he hadn't touched them, but I could be wrong. I put them back in the same number of turns that they came out with. But don't know if that was the stock setting. Parts will be in the sled on Monday and we are expecting snow that day also. Still hoping for an answer on which side of the pentagon shaped pump the small diaphragms go on cause I forgot to mark them when I took out the damaged ones. If not I'll bring the pump to a local sled shop for an answer. Thanks

by the way the carbs seemed to react perfect every time I opened the throttle with my fingers after I cleaned them.
 

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jeff.schulze said:
yep all for free. But they hadn't been ridden in forever so each has its own problems, although I have had all of them running. The 120 is a riot for my 4 and 5 year old kids. Both plugs are dark and damp but not really soaked when I pull them, the clutch side plug seems a bit darker though. I have no idea if the former owner messed with the two adjusting screws on the carbs. I know you can lean or rich it up a bit with those, I counted the turns when I took them out. They both turned out the same amount so I assumed he hadn't touched them, but I could be wrong. I put them back in the same number of turns that they came out with. But don't know if that was the stock setting. Parts will be in the sled on Monday and we are expecting snow that day also. Still hoping for an answer on which side of the pentagon shaped pump the small diaphragms go on cause I forgot to mark them when I took out the damaged ones. If not I'll bring the pump to a local sled shop for an answer. Thanks

by the way the carbs seemed to react perfect every time I opened the throttle with my fingers after I cleaned them.
I'm taking it that by you saying, (quote) by the way the carbs seemed to react perfect every time I opened the throttle with my fingers after I cleaned them. You synchornized the carbs?. If not syncrohnize the carbs. If that is what you meant perfect. Now set the needle jets in the 3 rd slot(or middle) to start. Needle jets are set accordingly to elevation, if you are 6000 ft above sea level set the needle jet down to the first or second slot. Set the fuel air mixture screws to 1 1/2 turns out to start, and set the idle 1 3/4 turns in after they touch the slides. If it idles a little fast cold, don't worry about it. You want to set the idle up when the machine is warm (been driven for awhile). The airscrews, if you adjust these in 1/4 turn at a time from 1 1/2 it increases fuel and less air to the engine (will make plugs black if too much fuel). If you turn them out 1/4 turn from 1 1/2 at a time it will make your engine leaner. If this is too extreme your plugs will appear white( or not good). Try that before you start buying or rebuilding pumps. Let me know if this helps
 

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Discussion Starter · #12 ·
I was told from a buddy that I didn't have to mess with syncing the carbs because its just the one throttle cable that runs both carbs, not separate cables. He did say that if I messed with separating the two carbs at all while cleaning them then I would have to sync them, was he wrong. Do I need to sync them and if so how do I go about that process?
 

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Discussion Starter · #13 ·
alright so I rebuilt the fuel pump, ran the fuel screws all the way in and then backed them out one turn, set the idle screw in 1 3\4 from contact with throttle linkage, have all new fuel lines, new fuel pickup, new plugs and of course she started up on the first tug. Problem is still there though. She seems to pop, not real loud, at an idle. Then the pop will go away, then it may come right back, then goes away again. I had it on a stand and had the mph up to 80 and it sounded strong and healthy. But It comes out of the hole for crap. I have to gradually give it gas to get going. Then at around 10 or 15 mph it takes of and runs like it should. When I let off the gas and get close to a stop it is raspy, not backfiring, but rough. I have messed with the fuel screws, out 1\4 at a time. The plugs seem to be getting whiter but shouldn't they be getting blacker as I turn out. The mechanic at a local sled shop said that if they adjuster screws are between the slides and the engine turning them out will add fuel. Between the airbox and the slides would add more air by turning them out. Is this right? Either way the sled seems to be reacting the same even with the adjustments. Am I barking up the wrong tree? Clutch problems maybe? Please help, winter in the midwest is slipping away. What are the symptoms of bad reed valves?
 

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Sounds like you need to fill the gas tank full of Premium gas, find a nice long field or open stretch of road that you can just open that sled up and just run alot of that s*** through it. Just needs all that old fuel and waste thats in fuel to go completey through everything. Any fields with deep snow would work just as good. Just my 2 cents
 

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You might have to drop your needles one clip,the lower the needle is the leaner it will be on the bottom end/mid range. Assuming it is loading up? If it is lean raise them 1 clip.
 

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this might sound dumb but have you checked to make sure there is nothing partly blocking the exhaust, if they were sitting for a while you never know what could have built something in there. this happend to my chain saw and quad after sitting over just the winter. idled fine but you would go to open them up and they would puke. just a thougth.
 

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Discussion Starter · #17 ·
I have already drained the tank completely, and refilled with premium so don't know if that's it. I wish it was though. I pulled the reed valves today and really found nothing. One of the pedals was pretty blackened but it cleaned right off. No rips or breaks though. On the carb side of the reed pedals was some black marks too. [not on the pedals but on the plastic behind them] That sorta has me wondering cause that charge from the combustion chamber shouldn't be able to make it back passed the reed pedals, should it? Anyway, the sled ran no different after new plugs went in and the reed valves were reinstalled. I'm gonna clean the carbs one last time just in case. But first I will take xlt man's advice and rip the pipe off to make sure everything is clear on the exhaust side. Passed that, I feel like i have covered most every base and think i may have to bring it in to the experts at the sled shop. So don't want to be railed but if I must...
I will double check all the carb settings when im in there again but just feel that since this is a totally stock sled I should be able to make it run right with the stock settings. Any other suggestions will be greatly appreciated cause I'm about to throw in the towel.Thanks
 

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When you cleaned the carbs have taken the pilot jet out and cleaned it? I always get a small wire and run through my jets just in case there might be build up in them. The best thing you can do with carbs and jets is to soak them in an aluminum friendly solvent to make sure the ports in the carb come clean. I usually soak them over night and then take a blowgun and blow through all ports and jets. Don't soak the floats though. Over the summer I worked on a 1968 motorcycle that sat for twenty years and got the carb cleaned. It was clogged with all kinds of crap and I had to soak it for a week. The guy took it home put it on and got it running fine. jmo
 

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jeff.schulze said:
alright so I rebuilt the fuel pump, ran the fuel screws all the way in and then backed them out one turn, set the idle screw in 1 3\4 from contact with throttle linkage, have all new fuel lines, new fuel pickup, new plugs and of course she started up on the first tug. Problem is still there though. She seems to pop, not real loud, at an idle. Then the pop will go away, then it may come right back, then goes away again. I had it on a stand and had the mph up to 80 and it sounded strong and healthy. But It comes out of the hole for crap. I have to gradually give it gas to get going. Then at around 10 or 15 mph it takes of and runs like it should. When I let off the gas and get close to a stop it is raspy, not backfiring, but rough. I have messed with the fuel screws, out 1\4 at a time. The plugs seem to be getting whiter but shouldn't they be getting blacker as I turn out. The mechanic at a local sled shop said that if they adjuster screws are between the slides and the engine turning them out will add fuel. Between the airbox and the slides would add more air by turning them out. Is this right? Either way the sled seems to be reacting the same even with the adjustments. Am I barking up the wrong tree? Clutch problems maybe? Please help, winter in the midwest is slipping away. What are the symptoms of bad reed valves?
Wrong!! The more you adjust the air/fuel mixture screw out the more air or leaner the fuel(white spark plugs) turn the fuel mixture screws back in 1/4 turn at a time until you find brown. This doesn't happen 2 minutes at a time. I wouldn't expect a 500 to scare me, but I would expect it to give me a fun ride in a hurry. Set the air mixture screw from original setttings, run it for awhile and check the plugs(white) in 1/4 turn, black(out 1/4 turn)... Geeze I'll RACE YA...lol. P.S. Check the reeds in this machine. 2 strokes don't pop. Maybe timing advance has issues
 

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It could be an electrical problem. All that carb cleaning and adding fresh gas should have solved any fuel problems.
 
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