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Back to the 98 Sportsman 500 4x4??? Compression = 50 max.

  
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Back to the 98 Sportsman 500 4x4??? Compression = 50 max.

 
serenescapes serenescapes
New User | Posts: 14 | Joined: 11/10
Posted: 12/05/10
07:50 PM

I cleaned the carb as suggested by Wolf. I am still getting alot of blowback from the lower end breather, actually a lot of oil coming into breather box from breather hose. When the hose is stopped up my bike seemed to start easier. So I thought maybe the back pressure was raising the compression. Well I tried the compression today. Bad news Frown  only 50 p.s.i. max... So without a tear down I guess I am asking from these symptoms, what might the compression problem be? I don't have any smoke from the bike, running hard or idling. The bike will run, but seems to lack power on the initial take off, then it runs normally?? What are my options without spending money on a rebuild kit and not really knowing if that is the fix? Any tips will be much appreciated. Thanks ahead of time.  

 
mikelm14 mikelm14
Guru | Posts: 895 | Joined: 07/09
Posted: 12/05/10
10:34 PM

Only 50psi and it's still running. It sounds like it's leaking compression from the piston/cylinder and building up pressure in the crankcase. This would cause the crankcase breather hose to vent off the pressure thus oil flowing into the breather box. This is what I'm thinking but Wolf may have a better idea on it.  
DISCLAIMER: REPAIR ADVICE IS GIVEN FREELY, I CANNOT ATTEST TO YOUR MECHANICAL ABILITY, FOLLOW AT YOUR OWN RISK

 
serenescapes serenescapes
New User | Posts: 14 | Joined: 11/10
Posted: 12/06/10
08:05 PM

So what causes that?? Is it as simple as a rebuild kit with new rings, or something more involved? Or is it one of those pull it apart and find out deals?  

 
philjbergman philjbergman
New User | Posts: 20 | Joined: 10/10
Posted: 12/07/10
11:40 AM

The Polaris 500cc engine has a compression release built into that cam that doesn't allow you to use a compression guage. I have only seen (3) 500cc motors that have needed rebuilt in the 7 years I have been a Polaris mechanic. Non of these died of natural causes, one a rival shop didn't tighten a valve adjusting nut, the other was drained of oil and not filled back up, and the other was sank in mud and ran for 2 days. If you really want to check compression you would have to take the cam cover off the left side of the motor and take the decompression lever out of the cam. I seriously doubt your motor needs anything. You should have a 142.5 main jet, 42.5 piolet jet, your air screw should be at 2 turns out, your poilet air jet should be 160. Check to make sure you don't have an intake leak by spraying carb cleaner over the carburator and intake.  
Visit hit-the-gas.com for Polaris Service Kits, Repair Kits, and Polaris OEM Parts diagrams.

 
serenescapes serenescapes
New User | Posts: 14 | Joined: 11/10
Posted: 12/07/10
06:18 PM

Awesome man!! I will put her back together and see what happens. Maybe a jet kit for the carb would help. I take it you think the carb or pressure/fuel amount is the problem right? That may be what is causing the severe blow-back. While I'm thinking of it, do you think the fuel pump mechanism may be causing some of these problems? Maybe tarnished or junked up? I haven't taken it off yet to check the condition.  

 
philjbergman philjbergman
New User | Posts: 20 | Joined: 10/10
Posted: 12/08/10
10:54 AM

The fuel pump runs off of the intake pressure so if you have a intake leak your fuel pump would not work correctly. Also air would be sucked in before your carburator has time to correctly mix the air and fuel, causing it to run incorrectly.  
Visit hit-the-gas.com for Polaris Service Kits, Repair Kits, and Polaris OEM Parts diagrams.

 
mikelm14 mikelm14
Guru | Posts: 895 | Joined: 07/09
Posted: 12/08/10
11:33 AM

Philjbergman what about the oil coming from the breather hose? Also are you still a Polaris mechanic?  
DISCLAIMER: REPAIR ADVICE IS GIVEN FREELY, I CANNOT ATTEST TO YOUR MECHANICAL ABILITY, FOLLOW AT YOUR OWN RISK

 
philjbergman philjbergman
New User | Posts: 20 | Joined: 10/10
Posted: 12/09/10
11:50 AM

Oil coming from the breather hose could be three things. (1) the oil level inside the motor is too high (2) the machine has been rolled at one time (3) Possible broken ring or severly worn cylinder with incorrect timing or worn cam lobes. To have too much oil in your engine would be almost impossible with a dry sump enigine. Meaning the oil is stored in a oil tank and pumped in and out of the engine. The large fuel filter that sits on the left side of the engine near the oil filter is your crankcase vent filter. This filters purpose is to stop oil from getting in the airbox. Polaris recomends changing this every 15 hours, and everytime the machine is rolled it is common sense to change it. If a ring was broken or the cylinder worn and valves not working correctly it could possibly build up enough compression then force the compression downward and out the crankcase vent. Since his machine doesnt smoke and runs normally when warm tells me this is not the problem. I am a shop supervisor now.  
Visit hit-the-gas.com for Polaris Service Kits, Repair Kits, and Polaris OEM Parts diagrams.

 
mikelm14 mikelm14
Guru | Posts: 895 | Joined: 07/09
Posted: 12/09/10
01:13 PM

If it rolled wouldn't it also smoke?  
DISCLAIMER: REPAIR ADVICE IS GIVEN FREELY, I CANNOT ATTEST TO YOUR MECHANICAL ABILITY, FOLLOW AT YOUR OWN RISK

 
philjbergman philjbergman
New User | Posts: 20 | Joined: 10/10
Posted: 12/09/10
02:49 PM

Not typically, but If the carb could still function after the ATV was rolled and you left it running on it's side long enough for the oil pump to go dry for an extended period of time it could yes.  
Visit hit-the-gas.com for Polaris Service Kits, Repair Kits, and Polaris OEM Parts diagrams.

 
serenescapes serenescapes
New User | Posts: 14 | Joined: 11/10
Posted: 12/10/10
06:14 PM

I love the fact that you guys are exploring all the aspects/possibilities related to the problems I am having with this machine. I did replace that breather filter but it still filled up with oil. I also changed the oil thinking that maybe it was overfilled as you suggested. I was wondering if I put too much oil back in because of the reservoir and sump amount being 2 quarts or whatever it was, I put the full (2 quarts)amount in. When I checked the dipstick it did seem to have a little much, but not excessive. That's when we tried to get it started and still had blowback oil into the airbox. I will check the oil level again prior to starting, it has been so freakin cold here, I haven't tried to put her back together yet. I don't have a shop unfortunately. This machine does have 6,600 miles on it, but I repeat that it doesn't smoke in the slightest. So who knows, I will clean the fuel pump diaphrams and get the carb checked for intake leaks, I'll give her a shot and let you guys know what's up. Thanks again, you guys are really helping me understand these machines. I'm a small engine mechanic, but these things are a whole different beast.  

 
serenescapes serenescapes
New User | Posts: 14 | Joined: 11/10
Posted: 12/26/10
07:52 PM

I wanted to give an update to Phil and Mike. Got everything back together today, checked the oil and it was a bit high. So we drained the oil to get it to a normal level, also took off the fuel pump and tried to clean it. WOW, very dirty, and a bit of tarnish. Without a fuel pump kit we just cleaned it as best as possible and put it back together for now. Got everything back together and it seems to have been that damn fuel pump and the excess oil. It seems to be good now, we rode it for about an hour. Once again I wanted to thank you guys for your direction and knowledge, it will not be wasted!!  

 
mikelm14 mikelm14
Guru | Posts: 895 | Joined: 07/09
Posted: 01/05/11
09:30 PM

Glad you got it. I notice you said your a small engine mechanic, hobbytalk.com has a small engine section if you need any help or want to help out.  
DISCLAIMER: REPAIR ADVICE IS GIVEN FREELY, I CANNOT ATTEST TO YOUR MECHANICAL ABILITY, FOLLOW AT YOUR OWN RISK

 
serenescapes serenescapes
New User | Posts: 14 | Joined: 11/10
Posted: 01/17/11
06:19 PM

Thanks Mike. I will try it out for sure. Thanks again for all the previous direction.