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Discussion Starter #1
I have a quadrunner 250 that has recently had top end done, oversized piston and rings, cylinder bored to match, new valves, all new gaskets, carb cleaned and rebuilt, and now machine, will fire right up and run great until it warms up, then dies unless u feather throttle, and is very hard to start when warm.. Im going to double check my valves, but what else could cause this? It did run real rich when first run so i turn a/f screw down to 2 1/4, and took a washer out of needle, as there were two washers and a plastic spacer of some sort unter the clip.. what other causes are there, thanks..
 

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id run it a bit more on the rich side . . when something gets bored it needs a little more fuel.
 

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I am going through the same sort of problem and I am real curious to what could cause this as well. I was going to do the entire top end with timing chain but have not got around to it yet. I can tell you this that it was suggested I adjust the valves first and when I adjusted the valves it really made a difference and the machine would start and run better especially when hot. But about 25hrs of riding later the problem is starting to appear again. I did not have time to see if the valves were out of adjustment again which would tell me they are in need of replacement. I also suspect that my machine has a lot of hours on it but I do not know for sure. No Speedometer when I bought it. Please post what you find and I will do the same.
 

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By very hard to start, do you mean it cranks slower than when cold or it cranks normal and just won't start? If it cranks slow when warm my guess is the cyl was bored a little undersize and the piston expands and rubs on the cyl wall.
Mike
 

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Discussion Starter #5
it cranks normal, just wont fire, if u hold throttle on while cranking it will eventually fire, but will not stay running..
 

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Check for a faulty fuel petcock. When they go bad they can lead to all sorts of problems like backfiring, stalling, hesitation, power loss, poor idling, etc. When mine finally crapped out on my '00 300 KQ it refused to stay running without constant throttle. The minute i let off the throttle it would die. Anyhow, to rule out a faulty fuel petcock pull the vacuum line (Smaller Line) off at the fuel petcock. If fuel comes out the the vacuum line or the port where you removed that line then the fuel petcock is bad and should be replaced. Note: Do this test with the fuel petcock set in the (On) position and the atv not running.
 

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Check your valves,with the work you had done they are still wearing in.
 

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Also check the needle slide,the white plastic washer goes on top of needle and the spring sits on top of it,this is what holds the needle in place,if the plastic washer is under circlip its holdind the needle to high and letting it flood,if installed incorrectly the needle can cock sideways in the slide.
 

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Discussion Starter #9
i will check my valves again and petcock is on way, it was faulty and vents had been plugged to run as a normal shut off, on my needle the white thick washer is under the circlip and has/had a washer on either side of it, so it is really supposed to be above the circlip under the spring?
 

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Did you ever solve this issue? I'm having the same problem. I just rebuilt the top end cause it smoked like a freight train. But I think it was doing this befor I rebuilt it. I thought it was just fouling out from burning so much oil. Don't know much of a history cause I just bought it. I tried bypassing the fuel pump and connected directly to the petcock and put it on pri. Starts up fine then after idling beautifully for about a min it bogs down and dies. Then I can't restart without giving it some throttle. I did also go through the carb and cleaned it. I'm stumped.
 

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Also another note, the vacuum line to the petcock is dry. Also when I pull the line off that goes into the fuel pump after it dies it smokes a little out of the little plastic fitting on the carb.
 

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Please don’t reply to posts older then a year old, especially ones that are from 2013, (7 Years Old). They are considered inactive and you will not get a reply.


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