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Discussion Starter #1
  • I'm working on a 2012 Sportsman 500 H.O. that won't start. It has spark, a new carburetor with a good supply of fresh gasoline to it, a new fuel pump, and the compression is good (about 148 p.s.i.). Upon checking the spark plug after extended cranking, it's dry! Shouldn't the plug be wet with fuel after the engine cranks but doesn't start? Also, when I prime the cylinder with gas, the engine will start briefly, for about 2-3 seconds. I've made sure all air is out of the fuel lines from the tank to the carb, and seen fuel pulsing out of the supply line when it's removed from the filter right at the carb. So, have any of you had this experience with a similar (or same) Polaris? Have you ever bought a carburetor that was defective or non-functioning right out of the box? It's pretty obvious that there's no fuel being delivered by the carb to the cylinder. I'm focusing on the carb because the ignition system has been gone through completely, and there doesn't seem to be any intervention going on by the electronic safety nannies, like the ETC switch. It does have spark during cranking. Any advice is welcome. Thanks.
 

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Defective new carbs are not all that uncommon when buying the Cheap Shit Chinese carbs from Amazon, Ebay or other vendors. Some Chinese carbs are not too bad - Kun Fu, Standard of Japan, Mikiny and Dekni are fair quality (and there may be others), but it always makes me wonder why you replaced the carb with a cheap piece-o-crap instead of buying a quality Mikuni or Keihin replacement. Perhaps now you have an idea of why Amazon and Ebay carbs that "FIT" are so cheap. They are not guaranteed to function, only to fit. The function is up to the installer. With a few hours of tweaking and tuning - a hundred dollars of the correct style of jets, slide needles, needle jets and air jets it might be adjusted to function properly. Instead of spending $45 for junk, spend $570 and get the OEM style carb that will just bolt on and function with minimal adjustment or spend $300 to $400 for a quality replacement carb (maybe an Edlebrock) or just have the original carb repaired for $150 and enjoy riding instead of scratching your head and sitting on a 5 gal bucket trying to figure out what it needs to run.

You already have spark and compression and apparently spark at the right time (since it will fire when fuel is introduced into the air stream).

OH! and to answer the question about the shouldn't the plug be wet? No - the plug should not be wet! Liquid fuel does not burn - only the aromatics (vapor) burns - if the plug comes out wet, the engine is flooded. Other liquids vaporize better than gasoline, but are harder to store and may only be liquid when under pressure. Hydrogen vaporizes above -423 degrees F, Liquefied Natural Gas (LNG) vaporizes at -259*F, Liquefied Petroleum Gas (LPG) vaporizes at -44*F and butane vaporizes at 31.5*F - gasoline contains butane as one of the aromatics.

Science is fun - want to know why a gasoline engine is hard to start at below zero temperatures? Want to know why a gasoline engine will start at -40*F? Compressing air raises it's temperature - the increase in air temperature due to compression promotes the vaporization of the aromatics in gasoline which ignite with the spark at the spark plug. Simple!
 

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Discussion Starter #3
Thanks, Latebird, for your insight. I appreciate your time and effort. You make alot of sense. I think the owner of this Sportsman is going to buy a new Polaris carb. O.E.
 

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Unless the carb is somehow broken it is a lot cheaper to rebuild the original.
 

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Discussion Starter #5
Good idea, but I don't know if the owner still has the original carb. He should, I'll have to ask him. See, I didn't start this job, but it's up to me to finish it. One of those deals. Ha ha!
 
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