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Discussion Starter #1 (Edited)
Hi guys. I've read like 50 posts on here about fuel issues, but haven't found the answer!

I have a 2001 scrambler 500. First of all, I couldn't get the engine to start. Did a compression test and it only hit 40 psi. Turns out that the piston was heavily scored and rings were toast, with tons of mud in the engine. I had the motor bored out .50 over and put in a new Polaris piston and new rings. Had the dealer check the valves and they were good to go.

I ordered a Polaris brand carb rebuild kit and carb dipped it for 30 minutes, washed with water, and blew all ports out. Carb was clean as a whistle. Got the motor put back together, cleaned out all of the mud, did like 4 oil changes, put on new air filter, new plug, fresh gas, new fuel filter, and started running it. The Polaris fuel pump gaskets were shot and couldn't justify $45.00 for a rebuild kit. So, I hooked up a Briggs and Stratton plastic fuel pump I had laying around. She ran like a raped ape for the first couple of weeks. As time goes on, its having running issues and seems to be getting worse. It idles perfect. While giving it plenty of gas, she screams. But, say your coasting down a hill, not using the gas, then hit gas again and it starts to choke itself out, or sputters bad. You hit the gas and it wants to die. Let it idle for a couple of minutes and it starts running again. It also backfires after running when you shut the engine off. I've set the fuel mixture screw to 2 turns out (I'm near sea level). Plug is perfect color. It doesn't smoke either. Any idea's on what to do? What to check? What to adjust??? Please help!!!
 

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Check the float height. Put a long clear tube on the overflow tube at the bottom of the carb. Open the drain plug on the bottom of the carb. Make a loop with the hose going back up higher than the carb. That should show you where the float is. (I usually put it just below the top of the bowl) If the fuel level is much higher it will go out the overflow. I think there may be a video on youtube showing this also. My friend that is a mechanic showed me this. Some time you can bend the float tab to raise or lower it. It is a lot of work to make adjustments but it is worth it. We have set up a few 500 carbs like this. After you shut the drain plug, go for a ride, leaving the loop in the tube. Drain the tube first then check for any fuel in the loop after the ride. It should not be leaking any when the drain screw is closed tight. Assuming the carb kit had a new needle and seat it would be the float that causes this.

Maybe check the fuel valve on the bottom of the tank. Perhaps it got gummed up bad or is leaking? What jet came with the carb kit. I ran a 155 in the last 500 I set up. Ran great with stock muffler and air filter. When you find the cause, let us know what was wrong.
 

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Discussion Starter #4
OK, I'll try that. Thank you Ronin. I am wondering what jet I put in there.....The last rebuild kit I bought from the Polaris dealer didn't specify what jet came with it. So, I have no idea. I know it was different than the one that came out of it. I tried opening the gap a hair on the plug and I up'd the Idle a bit higher, but no change. In fact it might have been a little worse. I would think that if the engine is failing if it would not start, like last time, but it does start instantly and idles like no tomorrow...

I did a compression check today and it was at 45PSI (closed throttle). I know they have decompression pins, but shouldn't it still be higher than 45?
 

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I think the stock jet is 152.5 and the rebuild kits come with 155 for the ethanol fuel. Not sure what the compression should be. I think you have a fuel issue, not in the engine. Let us know if you get it fixed. Put a stock fuel pump on if you can to rule that out.
 
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