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By Chase Cook
Hi I just got an Polaris sportsman 500 4x4 ATV the other day. I got it real cheap but I started to go into it because it didn't have compression so I bought a new piston and ring kit for it and installed it, but now when I try to start it all it does is shoot fire out the exhaust or the intake of the carburetor. And a timing is top dead center.;I think I can't really tell another way if it is or not. when I put it together I made sure to piston was on top and the cam lobes where facing down where are the cam sprocket is facing up. It has gas and spark. It did start a couple minutes ago but it didn't stay running and now it won't start. Do you think the valve need to be adjusted more to close better?I'm fixing to try that out and if that don't work what is the problem? Also I made sure everything was together good and right and change the oil and changed out the radiator fluid.
I was reading another forum recently about fuel leaks and possibility of fire happening. Reminded me of an incident I had a few years ago while working at a Can Am dealership. The quad was a stolen & recovered Outlander 650 that had been tampered with. These quads have an electronic safety system, similar to their DESS system on the sleds. You cannot bypass the key switch and get spark without a computer with factory software. Anyway, I was trying to determine what was damaged since the thief had attempted to hot wire various electronic parts. I got all the extra wires removed and things looked back to stock. Pulled the spark plugs and was going to check for ignition and if the starter still worked. Well, they both worked alright and guess what - the cylinder was flooded with fuel! Instant flames with gas spraying all over...great!! I managed to use my hands to put out the fire, good thing I had on gloves (but choked they were ruined of course, haha). Seems it's possible to flood an engine with efi when you put power straight to the injectors, doh! As in much of life, you cannot take things for granted (I'd only seen carbs flood like that). And even though it had spark, the quad still needed a new ECM to run - that part alone was $1200. So lets hear your stories, crazy stuff happens every day I'm sure.
Tesla made an ATV to complement its Cybertruck they just showed off. Its called the Cyberquad and will only be available with the truck to start. Cool name "Cyberquad"... Has anyone seen this? Thoughts? All electric and plugs into the truck to charge.
Here's the Cybertruck introduction (Cyberquad ATV at 3:50)
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Hey guys, I sure hope someone can help me out here...
A few weeks ago, while we were out riding, Mini-Me's four wheeler started acting up. Anything above about ¼ throttle would make it bog real bad and if you didn’t back off the gas it would shut off. Seemed like it was starving for gas or air. No obvious fix on the trail so took it home figuring it was a fouled carb.
Took the carb off; not serviceable. Put it back on and the problem was gone. All I did was unbolt it, pull it out, cuss about the shaved screw heads, and put it back. Ran fine for a few days then did it again. Took carb off and put back on again (hell, it worked last time) and while I was at it I bought a good plug and replaced that. Didn’t fix it this time.
Ordered a new carb under waranty. Company took three weeks to send me the wrong part.
I ordered a new one myself which showed up Friday. Saturday morning I had him ride it pre-replacement to verify issue was still there; it was. Anything over ¼ gas it would bog and die.
Replaced carb (fyi – slightly larger – 20mm new vs. 19mm stock) and it was back up and running. Better then before, seemed a little quicker and sounded MUCH better.
For a few hours… Then the bog and stall came back. Below is everything I tried last night –
Took fuel line from tank straight to carb – bypassed filter/petcock – no change
Took crankcase line (that is hooked to the air filter with a check valve in-line) off case – no change
Took air filter completely off – no change
Gassed it until it started acting up and then started shutting down the choke (to much air?) – no change
Held the back end up (now it’s not “under load”) and revved it up – no change
Adjusted the idle up close (doing it by ear) to where it wanted to cut out when using the throttle – continued to idle fine; no bog. Blipped the throttle and it bogged down.
I’m going to go get a can of starter fluid to check for air leaks around intake, some carb cleaner to clean up the carb, and a new fuel filter to replace Chinese one. Don’t expect any of that to fix it, but ruling things out.
Also; this may not be related but….
The battery on this thing is a POS. When we pull it out in the morning it doesn’t have the juice to crank it, gotta “boost” it for ~5 min. before it will crank. Usually once boosted and we get it started it’s good the rest of the day. Well yesterday he shut it off and when he tried to start it again it wouldn’t bust off. I did a little investigating and discovered that if you hit the starter and give it some throttle it acts like the battery is dead (slow turnover, wont fire). But once you let off the gas, it spins over slow a time or two (clearing the pressure?) and then the revs start to pick up and it will start. Almost like it’s over pressure in the cylinder if you open the throttle…
Because of the above I’m thinking maybe an exhaust valve issue??? To tight, not letting pressure out fast enough maybe? Maybe that’s causing the bog when you give it gas??? I’m going to get a set of feeler gauges and check/adjust the valve clearance.
Again, don’t expect a magic fix but it’s something to look at. I know these things require periodic valve adjustment, but I can’t see it being out of whack at < 10 hours.
I was going to pull the plug, hook it up and ground it while I hit the starter to verify that I’m getting fire, but it starts and idles fine, so no sense in that. I’ll still pull to inspect (correct color, no oil, etc.) just for fun.
I don’t think it’s anything mechanical, symptoms/trouble shooting so far just don’t fit.
Which leaves electrical; the CDI boxes on these things are know issues, but 99% of the time they are good/no good. So why does it start/idle if that’s bad? I suppose it could be bad and only displaying once the revs come up, but that’s a LOOOOONG shot. Only $5 so if tonight’s tinkering doesn’t fix/isolate the issue I’ll probably get one just to say it’s been replaced.
Aside from the CDI there is a battery (for starting only), a magneto, a voltage regulator/rectifier, and a million electrical connections. I haven’t gone thru them all but I can’t believe it’s a bad connection or the magneto because of the repeatability of the problem. It doesn’t come and go on its own; it runs fine, then all of the sudden won’t come off idle without cutting out. Take the old carb off, put it back on; it’s fixed (for a while). Take the old carb off, put it back on, it’s not fixed. Take the old carb off, put a new one on; it’s fixed (for a while).
Which leads me back to mechanical, but I’ve checked (almost) all of that.
Small chance it’s the valve adjustment, but I’ll verify that tonight. If it jumped timing it would be jacked from idle so I don’t think that’s it, plus it showed up, went away, came back, etc... If timing was off it wouldn’t run at all, or would run like crap from idle on; correct?
Oh, also – When I started looking at it last night (right after it started acting up) the air intake (short, curved aluminum “tube” going from the carb to the head) was hot. REALLY HOT. Maybe he over heated it, but before I put the new carb on he test rode it cold and it still did it.
Short of a .40 thru the engine block, anything else you can think of? I’m running short on ideas after the above…
Has anyone tried the GPS XII Run Flat tires. We just got a set for hunting season and these are the best thing I have ever seen. If your looking for a tire that you don't have to worry about flats this is the tire. We have purchased many different brands for our machines over the years and nothing like these ever. A little on the pricy side but I have to say well worth every penny.
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