Hello. I've been looking at a 96 sportsman 500 for a neighbor. Hes had it for awhile. He replaced the cam/rocker in it due to the exhaust lobe wearing down. After the install, he told me it took forever to start, but ran well once it started. Frustrated with it, he parked it. That was 5 years ago.

So, when he dropped it off, the first thing I did was pull the carb and dismantle it for cleaning and a rebuild kit; it was pretty gross inside. While the carb waited for parts, I pulled the rocker cover, recoil housing cover, and cam cover to verify correct ignition and valve timing / lash. All was done right, valves are at a snug .006".
I cleaned and rebuilt the carb, set float height to manual specs, set a/f screw to 2.5 turns out, and reinstalled. Carb is spotless, all clear.

This thing will not even hint at starting, unless I remove the airbox lid and filter, and cover 90% of the intake plenum with my hand. Then, it'll cough, sputter, and fire up, run great for 3 seconds, (intake unobstructed) and die. Repeat the process, and my hand will be soaked in gas, and there'll be an occasional fireball out the intake...and that's as close as it has come to "running".

I've triple checked valve lash and timing. I've verified TDC on comp stroke. I'm getting healthy arc from the plug. Obviously there's fuel, but the necessity of clogging the intake makes me think it's fuel starved. At this point, I'm so confused, I can't think straight. Carb issue? Valve sticking open? Ignition timing? I'm sorry for the book post, just trying to provide as much info as possible, in hopes that someone will see this and be able to redirect me, or identify the issue.

Thanks in advance for all the tips and suggestions,
Ed

 

I guess you have checked fuel filter ( replaced ) and fuel pump and verified fuel pump has a good vacuum signal from carb and the vacuum line, and fuel lines are in good condition and connected correctly? I'm no Polaris expert but, there will be more in here to answer your questions soon....hang in there...

 

Hey, thanks for the reply. I did verify flow through filter, and double check line connections. I left the vacuum pulse line hooked up, and detached the fuel line. With the petcock on 'reserve', I thumbed the starter, and saw some fuel trickle out of the detached line. (I also "manually" tested the pump by actuating the diaphragm in the fuel pump by suck/blowing on the vaccuum line.) Carb is getting gas; after cranking on it for awhile, I can open the drain screw on the bowl, and empty the carb.
I'm really stumped on the restricted intake aspect of this. In my mind, restricting the air to get it to fire is a sign of being lean, i.e., not enough gas.
Again, thanks for the tips. My brain hurts because of this dumb machine!

 

Most common problem on these is if you have spark and fuel and won't run or will try to run,it may be the exhaust cam lobe. Look close on the lobe height against the two intake lobes. If it's scored,could be the problem. This was a common problem on all Magnum 425 and Sportsman 500 engines from 1997 to 2000 models. 2001 was the first HO model that had the improved cams and larger carbs. Here's one of the worst ones. Would idle,but pop back through the carb. Bad Cam Pic - ATVConnection.com ATV Enthusiast Community
Another problem related to the 500 was that some would pull start,but wouldn't electric start. This was because of weak pick up coils or pick up coils were too far away from the flywheel. This usually happened if pull start ropes ever broke and hit the pick up coil. You could "gently" tap the pick up coil bracket to move the coil inward a tad towards the flywheel and see if it helps. Same thing that happened to this member.no spark to plug when using electric starter - Page 3 - ATVConnection.com ATV Enthusiast Community

 

I know you have cleaned the carb, and you mentioned that you had to wait on parts so I'm assuming you installed a kit? Specifically, what parts did you replace? And if you replaced the pilot, main, jet needle...etc, did you compare the new to the old and ensure the new parts were the correct size? Anyway, I recommend you re-visit the carb, ensuring the jets are correct, float is set correctly and the carb is assembled correctly. I have attached a diagram of your year model. When it was together, air box lid on, did you have the vents connected to the airbox. And was the lid a good tight fit.
? Are all the choke componants there...is the choke cable adjusted correctly...did you thoroughly clean the choke passage in the carb and verify it was clear by spraying some brake cleaner thru it...and compressed air? Turn the idle adjuster up a turn, and try the air/fuel screw at 1.5 turns from seat. Anyway, lots of smart/experienced folks here, it will get figured it out.

 

Looking back at your first post saw that the cam had been replaced.. Sorry,missed that one. One thing I did forget was to say was to pull the black wire from the reverse limiter module as they can short out and not only cause one to die,can also retard ignition spark if they fail. Module is located right under the cdi module. Looks like this one.Polaris Sportsman 500 96 97 Hub Ground Box LR83 10643 | eBay Although you say you do have spark,no harm checking stator and pick up coil specs.Stator exciter wires Red to Green 3.2 ohms, Black/Red to Green 450 ohms,Pick up coil White to White/Red 97 ohms. Specs are +/- 20%. If these check out,pick up coil to flywheel tab distance is between .010-.040,fuel is getting to carb,still won't hit a lick,then still sounds like carb related problem. Carbs setting up that long sometimes are a pain. If you get frustrated and can't narrow it down,cheap knock off carbs are showing up now on ebay as a last resort.New Polaris Sportsman 500 Carburetor 4x4 ATV Quad Carb 1996 1998 Non HO Y | eBay
You can have spark,but it the flywheel key has sheared,timing will be off. Worth a look see and pull the reoil cover. You can check the pick up coil while you're there. Just back off the flywheel nut and see if the key has sheared and flywheel has moved. 500s were the main ones to do this. Just a thought..

 

Hey, Old Polaris Tech. Thanks very much for your detailed and thorough replies, much appreciated!

This machine's recoil unit is missing, actually. So, its possible that the gap on the flywheel/trigger coil is out of spec. I can check that along with the ohming the stator and checking that wire on the cdi.

I'm wondering if maybe the fuel pump is failing. When I pulled the supply line (vaccuum line still attached to carb) and cranked it, the stream of fuel was a small, slow trickle. I manually suck/blew the vac line, and the stream was similar, so who knows. Everything in my tired brain is telling it's fuel-starved.

Plug the intake, it sputters, runs, remove plug, dies in 3 seconds. [Like it's not getting near enough fuel with a fully open intake, fires on a covered carb, once the blockage is removed, the fuel supply can't keep up with the engine's appetite, and it dies].
The fuel dripping into the airbox after the engine dies, still confuses me.
Seems like lack of fuel to me, but I'll definitely check the aforementioned items as well.

Can I try bypassing the pump, hooking a tank line directly to the carb? If it is carb-related, at least I can remove that easily to check. Again, huge thanks to Old Polaris Tech, and everyone else who has taken the time to read this and offer input. Please don't hesitate to keep the suggestions coming. I've been working on small engines for years; never was a fan of the CV carburetor...
Thanks,
Ed

 

They can get trashed up over time and if the fuel supply isn't a steady or pulsing stream,I'd replace it as cheap as they are now.Fuel Pump for Polaris Sportsman 400 500 600 Magnum 325 Outlaw 450 Predator ATV | eBay Yes with the recoil off it's a good time to check the pick up coil and flywheel key while you're down there just as process of elimination. Hope it's either the pump or something simple. You can have a temp gas bottle hooked up and block off the carb vacuum port and see what happens first before you order a pump.Normally these old machines have to have the air box on and sealed tight also.

 

Ok, thanks again! I'll try this setup when I get back out to the garage. Might be worth mentioning that I tried to start the quad with the air filter/lid both on and off; no change in the (lack of) performance.
Thanks very much, your knowledge and time has been very appreciated thus far!
Ed

 

"This machine's recoil unit is missing, actually." How the devil are you trying to start it? Holding the bendix in place with a screw driver or something of that sort? Just curious..