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Hello and thanks for reading this post. I have a 2003 Arctic Cat 250 4 X 4 Utility ATV. It has been running very well all summer and into this fall....until a few days ago when it lost power at about 1/4 throttle. I checked the air flow and found no issues there (I replaced the spark plug at an oil change 2 months ago). There was about half a tank of fuel and the fuel valve was in the "On" position. This issue first happened Thursday evening when it was about 32 degrees outside. When I got off work Friday afternoon, I fired her up and she ran perfectly without me doing anything except starting and riding it....it was about 54 degrees on Friday afternoon. Saturday morning (32 degrees), I fired her up to saw and haul some firewood and the issue came back. It started fine and ran normally for about 3 - 4 minutes at idle and then riding out to the woods at 1/4 throttle and above, sputter and putter, as if starved for fuel. I limped to the woods in first gear and then back home the same way. Letting it sit for a few minutes would permit it to run properly (all the way up to full throttle) but only for a very short while and then it would sputter at 1/4 throttle. I figured maybe there was gunk in the carb or perhaps a cold weather related vacuum leak in the carb......so I swapped the carb out with a clean and properly functioning spare carb that I keep on hand (I also checked the fuel flow in the fuel line and it was fine and there is no fuel filter in the line)....and it ran perfectly for the rest of the day.....even hauled 3 cart loads of cherry firewood chunks with it (probably 500 pounds in each load) up a steep incline and it never missed a beat (it was about 40 degrees by that time).....so I figured it had been a dirty carb. This evening (45 degrees out) I fired her up to put out a little shelled corn for the deer and after a few minutes of riding, (slowly puttering around) the issue has returned....so I had to limp back home in first gear. It acts like it is starved for fuel.....so I even filled the fuel tank up and after that it would actually run in second gear but it still sputtered starting at 1/4 throttle.....but the full fuel tank did make a slight improvement in performance. Any ideas on things to troubleshoot would be greatly appreciated.
 

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It could be starving for fuel. Change fuel setting on petcock to RES and see if that makes a difference. There has been issues with petcocks plugging up and of course, limiting fuel flow.
 

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It could be starving for fuel. Change fuel setting on petcock to RES and see if that makes a difference. There has been issues with petcocks plugging up and of course, limiting fuel flow.
Thanks for the reply! I did move the petcock from "On" to "RES" this evening and it did not make a difference......I cycled the petcock through its full range of motion several times and then left it on "RES" but it did not help. Maybe I should just order a new petcock and start there. Just seems like the near freezing temps are playing a role too..... Thanks again.
 

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If you’ve done that I don’t think it’s the petcock then. When it starts starving for fuel have you given in a little choke? If so did that make a difference?
 

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If you’ve done that I don’t think it’s the petcock then. When it starts starving for fuel have you given in a little choke? If so did that make a difference?
I did try that and it doesn't help.....but that is expected because the choke on this particular machine (OEM as well as aftermarket carbs) is a bit odd.....at idle the main air intake "butterfly" is essentially completely closed and the choke mechanism pulls a little valve that closes off a tiny airway passage that, when open, allows a small amount of air to bypass the main intake......so when you throttle up and the main intake butterfly begins to open, the choke mechanism has essentially no effect on air flow......but when the throttle is "off" the choke cuts off the little bit of air that bypasses the main intake. I hope that makes sense. Essentially, and by design, the choke has no effect once you start to throttle up.
 

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I did try that and it doesn't help.....but that is expected because the choke on this particular machine (OEM as well as aftermarket carbs) is a bit odd.....at idle the main air intake "butterfly" is essentially completely closed and the choke mechanism pulls a little valve that closes off a tiny airway passage that, when open, allows a small amount of air to bypass the main intake......so when you throttle up and the main intake butterfly begins to open, the choke mechanism has essentially no effect on air flow......but when the throttle is "off" the choke cuts off the little bit of air that bypasses the main intake. I hope that makes sense. Essentially, and by design, the choke has no effect once you start to throttle up.
Update on my Cat's issue. I verified that fuel flow is not the issue. When the issue was occurring, I pulled the fuel line off at the carb fuel intake and fuel ran out the fuel line like nobody's business.....so it is not a fuel pressure / fuel flow to the carb problem (I had already swapped out the carb with a known to be working properly spare carb). After verifying the fuel flow was good, I noticed that the intake air pipe (makes the transition from the carb output to the cylinder head intake) was showing show tiny cracks and splits so I figured perhaps that was allowing air to leak into the fuel / air mixture right at the intake port of the head......so I replaced the air pipe / felt gasket / and O-ring that all serve to seal that pipe with new OEM parts. The machine ran perfectly after that new part install.....until the following day (yesterday) when the ambient air temperature was about 34 degrees rather than 40 + degrees the previous day. Unfortunately the issue remains......when the engine itself is cold and the ambient air temperature is low enough (somewhere around 40 degrees and below), the engine will start just fine and run properly for a few minutes......then while riding, once the engine RPM gets a little bit above idle, she sputters and putters, so I have to ride around just above idle until the engine gets warm enough and then the issue disappears. As the engine is warming up (it takes a while - 20 minutes or more), I am gradually able to run the RPM's up a little bit at a time until she finally runs properly. The issue definitely appears to be cold weather related. If it is a cold air infiltration issue, I don't know where else to check for leaks. If it is not cold air getting into the fuel / air mixture past the carb, I don't know where else to check for air / vacuum leaks.....any suggestions here? What other cold sensitive / potentially failing components (CDI - timing issue / some sensor issue - it is a 2003 so I don't think it has any emissions control crap....Suzuki made the engine for Cat back in the day so it is essentially the same machine as the old Suzuki King Quad 250 from the same year) do you think could cause this issue? This machine ran perfectly last winter all the way down to zero degrees F. I greatly appreciate any suggestions. I use this machine primarily for work (working up logs / hauling firewood , etc.) and puttering around the farm .....not for ripping and racing. Thanks. Guy
 

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Have you inspected the crankcase ventilation tubes and connections?
 

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Have you inspected the crankcase ventilation tubes and connections?
I checked one crankcase breather that runs from the crankcase into the air box and I pinched it off at the airbox and that did not help......but I need a second set of hands to pinch it off at the crankcase to see if that helps. I will have to trace out and check the other vent hoses. Thanks for the additional suggestion.
 
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