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Discussion Starter #1 (Edited)
My dad was given a 500 Sportsman that has issues(no wonder it was free), the gal had it to a stealer and he said camshaft. I don't believe anything they say but I don't ignore either. The thing starts and idles fine, no noises, knocks, clunks ect...that I've gotten used to with cam problems, it sounds like any other sportsman I've heard(which is where I question cam). If I give it throttle , it starts to rev up, then pops, bogs, falls flat on it back, and backfire. When I first got it running it would rev up fully in neutral, went for a drive and couldn't get it to rev at all, just wanted to pop, bog and backfire. Now won't rev even in neutral , but still idles fine. It acts like a throttle safety or rev limiter, but sounds different than the reverse limiter.

I have gone through the carb(done quite a few, know my way around them), I got it to run great idling. I am not familiar with Polaris , been building Japanese for years, cam chain looks tight, haven't torn into rocker cover yet, but trying to get some ideas as to what direction to go.

I know ECM, electrical safeties, fuel pump, timing and a few other thing can all cause this, but what area are more likely?

Thanks for any suggestions.
 

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Welcome to the board!:med:
 

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sounds like a bad cam those were common in the 90s models of the 500 If the unit is in decent shape and its free its worth a camshaft i would think. Pull the valve cover and see.
 

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Discussion Starter #5
Ya, the more reading I have been doing on these the more it is apparent to be the cam. I've heard cams out on several bikes/quads , all Yamaha, Honda,ect..., they all had a knock or loud tapping from the rocker hitting loose. This is the first that is completely quiet. I see there is a Scrambler 500 new cam on ebay for $75, is that the same cam? I also see some have 1996-2012 as the years the cam fits , and the next cam say 2000-2005. Doesn't make sense. Course it is crook-bay.

I found that the dealer that the lady had the quad to , took the brass brake line adaptors from the caliper in the rear, both lines where just hanging there and no adaptors.

Thanks.
 

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I'd check the VIN first on the frame under the left foot well to make sure exactly what year model you have. The cam is easy enough to check by removing the valve cover.
There are electrical problems that can make it act that way too. Make sure the ETC is adjusted correctly. Have you tried pressing the yellow reverse override button on the left handle bar when it cuts out? Could be the RPM limiter gone bad. A quick check is to disconnect the black wire coming off the limiter to the CDI. They often go bad on the 90 somethings and can make it act as you describe or do other weird stuff. Do the reverse and neutral lights work properly? A bad gear selector switch can cause the limiter to kick in when it shouldn't. Disconnecting the black wire disables the limiter and quickly eliminates those things as issues.
 

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Discussion Starter #7
It's a '97, When I had taken it for a spin the other night after cleaning and double checking the carb for issues I had played with the override button both in forward and reverse. It did the normal limiter miss in reverse and the button eliminated that but as the rpms came up it started popping just like in forward. That's why I stated it sounds like a limiter but is different than the reverse limit.

The neutral light does not come on, and I was wondering if it is supposed to start only when the hand brake is pulled in, even if it is in reverse, or should it start without touching the brake as long as it is in neutral? I can't remember how my Scramblers were.

I am going to reach in and take the valve cover off just to see about the cam since it is the most likely fault. I was really hoping for a less dismantling fix.

Is the Scramble 500 cam the same?
 

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It'll start in any gear and there is no brake safety switch although its good practice to hold it while starting. The cams are the same.
Be sure to let us know what you find.
 

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Discussion Starter #9 (Edited)
I took the cover off and the cam is rounding off. It still has most of the lobe but you can see it is no longer the smooth cylindrical ground finish, I was going to bring my dial indicator home from work today to measure lift but forgot, would have been hard to carry it home on the motorcycle anyway.

The starter will not engage without the hand brake pulled in so it has a brake safety , even in Neutral. I though my Scramblers always had that also. It could be the neutral switch is bad and it never thinks it is in neutral so the brake switch needs to over ride the safety. Otherwise I would think it shouldn't limit it in neutral. Now to start bidding and waiting to see if I can get one cheap.

Is there a better company (aftermarket) to get one directly, rather than fleebay? So many companies now sell so much overpriced on ebay so they won't sell like a normal company does anymore and give a decent deal direct.

Thanks
 

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I think but not sure but im thinking most folks replace their worn cams with the newer ho type cam which was supposed to be better.
 

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HO cam had different lift and was a much harder metal from what I have been told. Go HO.
 

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Cant use the HO cam unles you get the 40 mm carb and carb boots too, they just dont run right without the bigger carb, yours has a 34mm carb on it. Im speaking from expierience, I have done this to my 425, tried to use the 34mm carb at first, jetted it up and it still didnt run right, put the 40 on it and it runns great, I* have a 500HO motor in my 425.
 

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Discussion Starter #15
I kind of thought that carb seemed smaller than most of my big singles. 34mm must be just about maxed out. I bet adding a 40mm CVK would make a big difference even without using the HO cam. For my dad ,it doesn't need any added power, as long as it goes forward or reverse when the throttle is pushed will be fine. I would think any of the aftermarket cams would be better than the original and should be equal to the replacement one.

I'll have to twist the neutral wires together so it thinks the bulb is there, see if it'll start without the brake depressed then.



.
 

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i thought the older sp500 started in any gear i know theres a few years that do 2005? im pretty sure because ive ridden a few without it completely stock except tires im not sure what years they switched to neutral/park safety
 

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Discussion Starter #18
Well this one does have a brake safety, turn the key on ,hit the starter button=nothing, pull the hand brake in it starts, doesn't matter if in neutral or gear, the hand brake has to be pulled in for the starter to engage. Don't see why it would be put on by the previous owners so must have been there from new.
Others might have been jumped so they don't have a working safety so don't realize it is supposed to? I'm about 90% sure my '96 scrambler had it also and I hotwired it so it wouldn't work.
 

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like i said they were completely stock not the type of people to tampre with anything unless they can wear out to the point they short out or something along those lines they just didnt have one
 

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Discussion Starter #20
Anyways, now I've seen some ads for camshaft and rocker kits that say 1995-2012, but the oem parts numbers have a 2000 as a number change, is that new number just indicating when the setup was changed due to the problems and the newer cams do fit or do the aftermarket cams really only fit with issues in the older heads? I have to pick one up and don't care to send one back.

Thanks
 
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