Ever since I purchased this quad (used) I have had an issue where it seems to run OK at sea level but it sputters from 1/4 to full throttle when I get any altitude (up to 5000) I have tried almost everything I can find.

I mean it runs fine, full throttle up and down my street, around the lawn, etc, but I throw it in the truck and get to 5k and it sputters after a lap or two.

Not the fuel filter, air filter or kinked line or plug
tried leaner jets, moving needle down/up - didn't do anything
new cylinder piston and rings, ran a bit better but still sputters
new stator - no help
new carb - ran a bit better but still not acceptable

Only things that are left are the CDI or the reeds but the reeds "looked" fine. I also don't see any evidence of a speed limiter on the cdi.

I thought it might need a break in after the new top end so I added oil to the gas and that helped "even it out" to where its at now which is rideable but not something I would trust on a long trail ride or hill climb. Two-three tanks of gas have been through oil-free now but I am tired of spending $$ on a lemon.

Any other suggestions?

 

Hi
might be worth ringing the main dealer (quad makers ) and asking him the exact jet size for that sort of altitude as its not something you can just guess and throw in... they should be able to help... good luck

 

Never heard of leaning for high altitude. I'd try a bigger main jet.

 

Remove the two screws holding the air box on and see how it runs at 5k feet with no filter. If it runs better,you need to go leaner on the main jet if you can find em. Think stock was an 80 main jet? Also something I've had to do is open up the exhausts on some of the older ones from all the oil and carbon build up over the years. You can have it vatted or simply take a long bent punch and drive it through the tail pipe into the muffler itself to open it up. Brutal yes,but I've seen em come alive when you do this and remove the restriction.

 

I have a 78 and 76 main that I tried with the old carb. neither helped.

I will pull the exhaust and throw it in my parts washer for a few days then sandblast the insides or punch it out.

 

I sold the quad but i test rode it on my lawn before i did and it was sputtering. I took the carb off and cleaned it and changed the plug and it seemed to run OK. I think my daughter was fouling the plugs the way she was riding it, maybe combined with the altitude. I had taken the air breather off at altitude but I couldn't really test ride t without getting a bucket sand in the engine so I just jetted down to no avail. Wasn't the oil either as I premixed for a few tanks and disconnected the pump.

Either way I sold it and picked up a Sportsman 90 4stroke. It didn't idle when I bought it but covering what appeared to be the float bowl vent by the choke with a plug fixed the idle. I could not find anything in the service manual about this vent except that there are pictures with a tube attached leading back.

Anything I can do to get some more power out of it without spending a fortune on a bigger carb and pipes?

 

This little tube on the top of the carb is never really explained in the manuals. It's just some kind of vent that was probably used on other brand applications,but blocked off with a small red plug on all the Polaris atvs..

 

On the sportsman 90 its a direct vent to the float bowl. You can see light from the bowl when the vent is unplugged. On the 50cc its a location for vacuum. It just goes straight into the venture through a tiny hole. I still have a 50cc carb and I remember it had the red plug on it when I bought it. The one on the sportsman should go to the airbox or maybe a carbon can but it seems to work fine when plugged and there is no provision for it to connect elsewhere.

Hope someone finds their answer from my trials with these two machines.

 

On the 2 strokes the carbs had the red block off plug and tube,no line went to the air box.#3 and 4 http://www.cyclepartswarehouse.com/f...2005&fveh=5660
On the first year model they don't show this,but on the 2002 and later model 50's and 90's they do. They changed the parts diagram and drew em in.Didn't draw em too well and at the wrong place also.... http://www.cyclepartswarehouse.com/f...2002&fveh=5591 All this depends if you have an oem Polaris carb or one of the many sold on Ebay as replacements.