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Discussion Starter #1
I’m finishing up restoring a 2004 Sportsman 500. It runs great once warmed up, but compared to my other 3 similar Polaris ATVs, it seems sort of “cold blooded”, meaning it doesn’t start without choke when cold (the others all fire right up on all but the coldest mornings without choke), and it takes quite a long time running on various amounts of choke to warm up to running temperate so it doesn’t bog. Again, once warm, it runs great, spark plug looks great once removed, will run strong and idle forever once warm. I went through the carb and cleaned it thoroughly during the restore. All parts looked fine, it wasn’t even very dirty when I did it. The only thing different about this one is that the fuel/air mixture screw plug was still in the carb, so I left it in, which means I haven’t adjusted fuel/air away from factory settings. I believe this is the original Mikuni carb that came with the machine. Would the factory fuel/air setting cause this? Should I get the plug out and adjust the fuel/air mixture?
 

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Discussion Starter #3
Wasn’t expecting that answer. But, I guess that’s why I’m on the forum, to pick the brains of people who know more than me. I’ll check them as soon as the temp gets above 30 here. What should I expect to find that is causing this, too big a gap, or too small a gap? My guess is too much gap, and when it warms up the metal expands a little, closes the gap some, and it runs fine from then on.
 

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The valves in those overhead cam engines actually get tighter as the valve seats wear.
You'd be surprised how much quicker and easier they'll start when the valves are set correctly.
It happens so gradually you don't really notice it getting progressively harder to start and more cold natured. They'll usually start and run fine after warmed up.
 

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Discussion Starter #5
Wow! Adjusting the valves made a huge difference. I don’t have a gauge small enough to tell what they were set at, but I’m guessing around 0.002. After I set them to 0.006, it starts much easier with less choke, stays running, and warms up quicker. Not as perfect as my others, but much better.
 

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Glad to hear that improved it. I tend to set them a little loose rather than tight when setting them. So long as you have slight resistance on the feeler gauge its good. They will tighten a little with use anyway.
 
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