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Discussion Starter #1
I have a 1998 Indy 500 and was riding this morning and it was running fine and then bogged down and wouldn't rev above 6000 rpm or get over 30 mph. I did put 330 jets in to replace the stock 350's. it was really cold so i thought the jets might be part of it.
 

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Why did you replace the jets? Sounds like you leaned it out. 20 down is quite a bit and it would be amplified by cold temperatures.

Colder temps or lower altitude, you go up in jet size. (denser air needs more fuel)

Going to 330 from stock 350 is usually something you do if you are going over 5000 ft.
 

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Have to agree with Bear here. I went down to 340s because I was too rich for my area. I also use BR8ES equivalents instead of the BR9ES Polaris calls for. That one hotter plug and the one down jet is perfect for me and my area. Pages 5.15k-5.15p will tell you what jets you need for air and elevation or page 33 for the 500/500RMK.

http://www.vintagesnow.com/Polaris_files/96-98_Fuel_SM.pdf

Also here is a spark plug chart for if you want to do some testing if that will help.
64872
 

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Discussion Starter #4
I replaced the jets because it bogged down in warm weather when we go ice fishing. I figured out it was just a bad spark plug and it had only been running on one cylinder.
 

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Bad jets are not going to cause it to run on One Cylinder. That will be something else like a spark plug cap being loose or broken, a bad cdi, a bad stator, issue with the carbs especially on that one side. I would start with the plug caps and cut a 1/8th or a 1/4" inch off of it along with replacing the cap itself as those are cheap and can be had at any parts store.
 

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Look through the carbs or take the muffler off and look back through the Y pipe at the pistons. Yes, it can still run fine with a scored piston, but it can cause bogging, particularly when it is running lean.

I bought one of those bore-scopes that connect up to your phone. Really nice for inspecting inside the motor without taking it apart.

 
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