I was riding the other day and on the snap of fingers my 250 moto-4 started running crappy it lost power, started back firing and would stall out going up hills. The funny thing is it idles fine and most of the time it revs fine. its like if just doesn't have the power to pull its self. I working on it one day last week and I took it out for a test drive and it was doing the same thing, then all of a suddenly it just started running great, I road it for 30mins thought it was fixed and put it away the next day it was right back where it was running crappy.

I have been through the carb 3 time and have found nothing, I cleaned the **** pit. I have put two new spark plugs in it, and I have checked the timing. I have noticed when I pull the plug it is black but not wet. I have checked all the connections I can find but not luck. Has anyone every had this problem before that might be able to help me out, am almost at my wits end

 

i have a warrior 350 so i can easily say i have never had this problem. but on the other hand i was fouling spark plugs left and right. if you plug is black then it's carbon fouled (dry fouled). this means your air/fuel misture is off or your jetting is off. black means your running too rich (getting too much fuel) your plug should golden brown. i adjusted my air screw and put a bigger jet in it and the problem went away.

if you have a book on it look and see what the stock jet size is and how many turns your air/feul screw should be set at and write it down. the first thing you can do is turn your air/fuel screw all the way in and back it out counting the turns to the specified adjustment and see how it runs. if that doesn't work then you may have to change your jet size. if your running rich you may have to go down on your main jet size.

if that doesn't work i would start looking for an air leak somewhere. you can make it easier to find an air leak if you take a can of starting fluid and spray it where any air hoses would be around air box and carb to motor. if the idle goes high then you have an air leak.

 

I took the air/fuel screw all the way out yesterday and it ran the same as if it was screwed all the way in (does that make sense). Just to be sure I adjusting the right screw, this is the screw at the bottom of the carb that is hard to adjust, when taken out has a spring on it and shaped like a needle on one end. Does any one have a book that tells how many turns this should be set at..

 

yes that is the air/fuel screw. if you take it out or put in all the way in it won't make a difference really beacuse with it all the way out it will be getting too much air. and with it all the way in it will be getting too much fuel. my warrior's air/fuel screw setting is at 1 1/4 turns out. your best bet to do it with out a book is to take it all the way in until it lightly seats. then back it out to 2 turns out. see if it runs any better if not you have to keep turning it out a 1/4 turn at a time. if it starts to run better at more than 3 turns out you need to go up on your main jet size.

 

Thanks for the help!!!!

 

87 W offers good advice. I have the gen II 250 T-wolf and gen III beartracker. the engines are almost the same, but I do not know about carb in the Moto 4. The twolf as a vh26sm and the mixture screw is at the bottom. 1.25 turns out to start, I go 1.5 in winter. If it is wet oil fouled, you may have some blow by due to age or valves. Adjust valves? Hotter plug d6ea?

Weak ignition can foul the plugs as well, but I am electronically impaired. I know the 250's stators have been suspect, but you might want to check connections. There are several guys on here who helped me with ignition questions.

 

let us know how everything works out.

 

I bought a coil on ebay I'm waiting to get that before I tare down the carb again. The funny thing is when this problem started I had been riding it for 20mins and all the sudden it started this problem (in past years it has never done anything like this), missing and sputtering on acceleration real bad). then other day I was working on it and it suddenly started running great again, ran great all that day then next day right back where it was all this in a week. I kinda think it may be ignition, something breaking down. I called my local dealer and they said the coils in these 4-wheeler never go bad but I got one for 10 bucks figured I would eliminate that from my equation..

 

give it a shot and see what happens. and every coil for any motor will go bad. nothing electrical lasts forever.

 

Well that didn't work, the coil wasn't the problem. I know yall think it could be the jets but with it starting all at once and clearing up for a short while, makes me think it might be something else, plus i'm running straight stock everything. My compression tester wont fit in the hole it is to big. so I cant test that right now. Do you guys think it could be something in the top end of the motor causing this problem, values, rings, rods, head gasket.? I sprayed starter fluid all around the jug, intake, carb, and no response, so it seems I'm not sucking any air from the outside