I'll make this as short as I can. My grandson has a 1988 Trail Boss 4X4 250CC. A few years back, Carb, recoil starter and other parts were stolen from it. I am trying to get it going again. I found parts on eBay. I have it running. It starts as soon as you hit the starter. But it seems to be running real rich. I got new jets that the 1988 calls for. But I can't get it to idle unless I open the throttle a bit, it wont idle on the pilot jet alone.I have a lot of white smoke at all speeds, and a lot of oil coming out the muffler. It does not stall, but revs a little sluggish. I also have a little fuel blowback thru the carb inlet. Since there is no reed valve I wonder if I might have stuck rings. What do you think? The compression is 100PSI. Is there supposed to be measureable pressure fron the oil injection pump? I am an old Harley Hog man and don't know a lot about 2 Cycle engines. If I don't have you confused enough. let me know.

 

Bumping up for a man in need of assistance.

 

Hey 7haj3. I don't have an 88, but I have two 04 250s. I looked at Ronnies and the carbs for the 90 seem to be the same as mine. Have you cleaned the carb real good? A plugged idle air passage could cause it to run rich at idle. The idle mixture screw is an air screw, so it leans out as you turn it out. My manual says this should be turned out 1 turn. The carb could be running rich if the choke plunger is not sealing. Being the carb is quite old, the rubber seal on the plunger may not be sealing. At higher throttle settings, the needle on the slide meters fuel through the main jet. This is much the same as many street bikes. The oil pump does not create a high pressure. It is a low pressure pump that precisely meters the oil to the carb. At zero throttle setting, the line on the injection pump lever should line up with the line on the pump body. Hopefully this will give you something to start with. Let me know if you have any more questions.
I hope this helps you
BryceGTX

 

Hey, since this thing sat has any condensation or possibly water gotten into the crank case? white smoke has always meant water to me. Also if it sat too long make sure you drain out the old injector oil, or at least freshen it up with new stuff of the same brand. Is there a drain plug on the bottom of the case? also Pipes on these 2strokes can get soaked with oil, when you get it running correctly take it out and run it hard, and see if that doesn't burn some of that gunk out . Check your pump timing as brycegtx described just line up the marks. Hope some of this helps, sorry for the delay, this forum is full of good people. I'm new and love it.

 

I have already done all that is suggested and it still runs rich. The only way I can get it to run right is to remove the bolt in the throttle housing that I suppose limits the throttle valve height to prevent overreving. Then it runs fine and idles fine. The carb has a 45 pilot jet and the manual says to use a 35 pilot jet. Will that make much difference in, it won't idle with the bolt in the housing. you have to crack the throttle a little to get it to idle, and then it runs rich at all speeds. The smoke is not pure white, it is oil smoke. I have tried using the oil injection and a 40:1 mix and no change. The dealers, 3 in my area wont get a 35 pilot jet because they have to order 10. I am adding my other message I posted to this thread.

I disassembled the carb again today and found nothing wrong. I forgot to put the bolt in the throttle barrel that limits the height the throttle valve will raise to prevent overreving (I think that is what the bolt is for) and the engine would idle perfect and it would revup good and not run rich. I put the bolt back in and the same old problems again. What do you think I need to do ? Remember this is a used carburetor to replace the one that was stollen.

 

I have researched the Polaris Parts Catalog from 1985 thru 2000 and I dont find a carb with the bolt I am referring to. It may also be a bolt to hold the choke actuating lever. The carb is a Mukini, with 169 and 00 stamped on it, the engine side inside throat measures 28.5MM. Looking from the airbox toward engine the idle screw is on the left side the fuel inlet is on the left side, the pilot jet air screw is on the right side, and the choke is on the right side but is different from the Polaris pictures. the choke stem has a small hole in it like where a lift arm link would attach, my choke cable does not fit it. The person I got the carb from said it came off a 1990 Trail Boss, but I wonder if he was wrong. The carb has a 145 main jet, a 45 pilot jet, a O4 needle jet and a 5DP7 needle.

 

To start with your pilot jet is to big. It should be a #40 and yes this will make a big difference. If you want to order or see the correct parts and part numbers go to Partsland.com. Go to the atv section and this will break all the atv's down by year and model. Then you can click on the parts area you want to look at. It will break all the parts down by number, price and picture. Good luck!

 

Thanks to everyone for your help. I have been there done that and every thing except replace the 45 pilot jet with a 35 like the manual calls for. The reason I have not changed it is my 3 dealers will not order one because they have to order min of 10. I will order one from Partsland, I was waiting to see if you thought it might correct my problem. I have a 1988 Parts and Owners manual. I thought the last time I cleaned and reinstalled the carb, that I had it fixed, it idled perfect, reved perfect and then I noticed I had left the bolt out that holds the choke lever on. It was sucking enough air thru the hole to lean it and make it run good. I put the bolt back in to cover the hole and I got the same old problem, won't idle and runs real rich. So if you think the 35 pilot jet will cure the problem I am ordering one.
Jay

 

One thing we also didn't address is the e clip position on the needle, there should be five slots start in the center one. If the setting is too low the needle will come off the main jet causing a rich situation. good luck, sounds like you've got it.

 

I had already raised the e clip to the top groove and it seemed to help some. Maybe the 35 pilot jet will cure the problem, when I get one. Thanks, but if you think of anything else I wil be watching this thread.
Jay