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Discussion Starter #1
Hello all, new to forums.
I am writing in regards to a problem I am having with my dirtbike. I live at an elevation of 5300 feet and am wondering what size jet I should use. The stock is a 160. 160 had always worked fine at this elevation and higher elevations. A couple weeks ago I was up in the mountains and my dirtbike would foul out at wide open throttle. It would not die completely. If I turn the gas if it will run fine until it runs out. Anyone know why this is happening. I fired it up where I live at 5300 and it does the same thing it will run fine but as soon as I give it full throttle it just dies out. I can turn the gas off and it will run perfect until the gas in the line and bowl is used. I checked my petcock and it works perfect. Pulled the bowl off of the carb and the floats are working fine. Any help would be greatly appreciated.
 

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weather

what kind of weather conditions are you having up there? air density can play a factor, especially if the air is thin. is your air filter clean? did you change filter oils?

are you running the same heat range plug you always have? same gas, premix oil, ratio? carbs usually dont just become out of spec like that.

160 MJ should be right and since its only up top(which is odd) then your needle clip positions arent gonna do you any good. your air screw should be about 1.5 turns out, you could play with that a bit. more turns out, more air, less turns. less air etc. not really sure if that would do anything for your top end at wot. I would check into gas/oil. maybe you got gas from a different station that has poor quality. Ive gotten cheap gas in my truck before and it took a full tank to drive 4hrs, but on the way back with new gas only half a tank.

matt
 

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Discussion Starter #3
When this happened I was using my friends gas. I changed the plug and put new gas into it. I cleaned my airfilter also and still have the problem. I think it is strange that it will run fine when I turn the gas off.
 

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not sure

Im not sure but its probobly leaning out when you have the pet **** turned off because its gravity feed and you are not venting it anymore. im not really sure because that is odd. Id first try one heat range hotter on the plug and see where that gets you, if it doesnt help go back and maybe try a smaller main jet. its really guess and check. you could try to do a plug test. If you have a nice open area to ride put a new plug in your bike and then start up and ride to the top of first then the top of second and shut the motor off while still accelerating and pull the plug out. ive never had to do this but im told other people have to check the plug. how much gas have you run through it since you used your friends gas? and what kind of gas/oil did he use and what ratio was it mixed? you could also play with your ratio. ive always run 32:1 and its worked good for me.

another remote possiblilty that could just be unrelated to your gas is the ignition system has a problem at high rpms. you could have a weak spark and your air/fuel mix is fine just the spark is hot enough and gets put out.

sorry i cant be more help
matt
 
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