Tork, read your post regarding wear on needle jet and needle leading to fouling at idle. I've read this from other places on the net. I have a 2000 AC 250, bought it used from a guy who used it for snow plowing side walks at his resort. This amounts to lots of idle and quarter thottle use - the things I've read eat needle jets on atvs. Been trying to solve plug fouling problem that occurs at idle to 1/8 thottle use. Plug fouls beyond use after several weeks of use. Checked the needle circuit - 1/4 to 3/4 thottle - plug burns grey. WOT test plug burns grey. Run at 1/8 thottle - plug turns black and sotty. Tried putting in a smaller pilot jet - but still black at idle and fouling. Also changing needle position dosn't help. Guys at the shop adjusted valves - no help. They also tried several smaller main jets - no help (plugs were burning white!). Dosn't seem to have any air leaks - boots look good. I really think its the needle jet thats worn. The guys at the shop say you can't replace the needle jet - would have to get a new carb. I found replacement needle jets for this carb (BST31 - 135A) at brownsleisureworld.com. My question is can the needle jet be removed and if so how? I thought about just replacing the needle, but from what I've read, would probably not help much as it's the soft brass in the needle jet that wears oblong. Anyway, other than the fouling problem and eating up spark plugs - the cat runs great through out all circuits. Thanks again, Tork, for your insightful posts and to the rest of the users of this forum. PS - I'm riding at 7000 to 9000 ft, 127.5 main jet, 3rd needle position, 137.5 pilot at 2 turns out, float adjusted to factory, freshly cleaned air filter.
Your dealer must not be very familiar with carb work or they like to sell carbs, you are correct that the brass tube will show the most wear. I would bet you get the needle and tube replaced and your problem will go away.
Tork, just finished installing new needle jet and needle. Still running a little rich in the pilot circuit but not as bad. I had to turn up the idle speed about one turn. Still some black soot on plug at idle to 1/8 throttle. Didn't mess with the fuel mixture screw or the pilot jet. I don't know if going back to the stock 145 pilot jet would help. Seems like that would richen the pilot circuit. Didn't put in the 130 main yet. Wanted to make one change at a time, but will need to put it in as plug is white at full thottle. Anyway, I won't know if this will solve the fouling problem until I ride the bike a lot. But the fact that it wouldn't idle with the new needle jet and the same settings tells me the old jet was worn and letting a larger drop of gas pass. Let me know if you have any other thoughts on this issue.
I would put 130 main jet in and try first, 145 pilot would make it richer, I will try to get pilot specs at work tomorrow. Sorry I haven't responded quicker, I've been gone on a youth group ski trip and just got back. Have a lot of catching up to do. Talk to you later.
Thanks for the reply, Tork. Glad to here you're helping out the youth. How was the skiing? Most the ski areas here in Colorado received 8 inches of snow last night. Windy and cold today. I'll put that 130 main in and let you know how it runs.
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. FordŽ is a registered trademark of the Ford Motor Company