I did some searching and couldn't figure this out.  My son and I were riding our CR250's (his is the 2001 and has a stock TMX carb) and having a great time.  We were on a wide, open type of trail - lots of wide open throttle - when suddenly he stops in front of me.  Turns out that his bike was suddenly holding a high throttle and he reported that the throttle was sticking.  I felt it and he was right - it wouldn't release all the way, and felt like it would "stick" when you first try to give it throttle.

I started the bike and it idled really high, so I killed it and checked for a kinked throttle cable.  Nothing.  Everything appeared to be fine.  I took it for a spin and it ran kind of gurgly, like it was missing or something, and wouldn't idle down.  I pinned the gas wide open for a second and then let off, then the throttle started working fine again.  We managed to get the bike back to the parking lot, but it runs, then burbles and dies.  The cycle repeats.  If we wait a moment we can restart it, but then it happens again.  Note - we finished our gas can into my bike and topped his up with fresh premium fuel from a busy gas station.  We put 1 gallon in our van to flush the 87 out of the pump lines, then filled the can (yes, I'm positive I put pre-mix in).  Also, recently replaced the float and seat, and have ridden it since.

Got home and pulled the carb.  Found that the needle has gouges on it, which fits that feeling that it maybe got jammed in the nozzle somehow.  But why all of the sudden, and why does it run like crap now?  Jets don't appear to be clogged, and the float and seat look perfect.  I thought maybe bad gas, but that wouldn't cause the needle to jam and scrape in the nozzle, and we were several miles out when this suddenly happened.  Thanks for any ideas...

Eric

Perhaps you bent the needle some when you replaced float and seat? That should have showed up from the start however.

Thanks for that feedback.  I looked at the needle and it looks pretty straight to me!  I gave a ring to the guys who are really good to me at the parts desk at my local dealer and I'm planning to bring the carb in to have them take a look (they're good to me like that).  They thought that maybe something go sucked through the carb and jammed the needle.  I'm about to go pull my reeds and take those with me too - maybe something got sucked through and damaged a reed??

I'll report back what I figure out.  Any more thoughts from anyone would be most appreciated!

So I pulled my (my son's, lol) reeds and found that one was chunked off on a corner, but maybe not even enough to prevent a seal.  Dang, I sure wish I could find an obvious problem here!  Anyway, the guys at the dealership agreed that the needle is trashed, and we figured out that something must have gotten sucked in that jammed that needle up!  I ordered up a new needle, plus the tube it goes into, and some new reeds.  I will clean the carb very thoroughly and then put the whole thing back together and cross my fingers!

Once again, any thoughts from you guys would be appreciated!!

Thanks,
Eric

Don't even consider starting it again without a Visufilter in the fuel line. You really should have known.

3 letters,

PWK

Okay guys, so here's the latest.  I installed new reeds, a new needle, and all new hoses (since I had it all apart anyway).  I cleaned the air filter and took the whole airbox out and completely cleaned that too.  I disassembled the carb as far as I could and cleaned it inside and out.  Suspecting that gas might be an issue, I cleaned out a glass pickle jar and drained gas out of the tank into the jar, then capped it and let the jar sit for a while to see if it appeared to have water or maybe some other contaminants - it looked perfect.  I did order a new nozzle too since the needle obviously had been jammed into it, but that is on back order until July (ouch), and the one I have appeared undamaged visually.  I also had a guy at the dealer help me check the float height, and that is right where it's supposed to be.

So, with everything super clean and all put back together, the bike starts right up, but it will only run for a few seconds and then it's like someone hit the kill switch - it just dies.  It will start right back up, but it seems like it only wants to run for a certain amount of time, around 5 - 10 seconds if only at idle, or a little less if you blip the throttle a little...kinda like if it only has a certain amount of gas to use and then the engine quits.  I just don't get it - there was the big, sudden issue with the throttle (caused by the needle jamming somehow), and now the thing just doesn't want to run.  I have very few hours on a new top end, and there is a ton of compression.  I just don't know what the problem could be, and am seriously thinking about just finding a PWK to swap out for this TMX.  Anybody care to chip in their thoughts please??  THANKS!

No chance this has something to do with ignition?

Thanks for chipping in a thought Jimmy.  I thought about that too...but it all started at one particular time when the throttle got jammed up and then the carb needle was gouged afterwards.  That was a physical problem, and up until that moment it ran just fine.  Now the running problem (starts fine, but just quits after a short time) seems like a pattern that is repeating itself.  I feel like the problem is right in front of me but I just can't figure it out and my son and I want to ride!!  Grrrrr....

What about the petcock? Did you take it apart and clean it? Reed block gasket? Bolts on reed block torqued to spec? Air leak somewhere?

shrubitup, on 12 June 2012 - 04:11 AM, said:

That is what I was just thinking.  If there is a clog there, it could be emptying the Carb float bowl of fuel and killing the engine, then it starts back up after the float bowl fills back up.

A plugged vent line on the gas cap will do funky stuff too......

shrubitup, on 12 June 2012 - 04:11 AM, said:

frdbtr, on 12 June 2012 - 05:43 AM, said:

seanmx57, on 12 June 2012 - 09:29 AM, said:

Thanks for the ideas guys.  I did just replace the reeds, and was very careful when I reinstalled the reed block, so I don't think that's an issue.  When I drained some fuel into a glass jar to look for possible water or other contamination, the fuel flowed nicely out of the fuel line, so I don't think it's an issue with the petcock or vent tube.  It really does seem like an issue with the carb not being able to supply enough fuel - but that doesn't fit with a sudden jammed throttle and now this running issue.

When I started it cold it didn't want to start or run at all with the choke on, so when I started it with the choke off, the exhaust had a lot of smoke.  I wonder if maybe the needle got jammed in the nozzle (the brass tube that the needle slides into which has a jet on the bottom) due to some dirt or something, and then maybe the nozzle got damaged a little bit (it's the only thing related that I couldn't replace since it's on back-order until mid-july), and now that's allowing it to run super rich, emptying the bowl quickly.  The nozzle looked okay when we checked it, but I know it wouldn't take much damage to allow a lot more fuel to flow up into the airstream!  At this point I'm thinking it's that nozzle...do you guys agree??  Any ideas on where I could get one right away?

Edited by ericinmichigan, 12 June 2012 - 06:17 PM.

while your gas weren't fouled in the pickle jar test you don't know for certain that the intake screen on the petcock isn't clogged somehow. Check that. Or maybe you did? How long did you let the fuel run into said jar?

run away sparatic throttle + cutting off/ starving of fuel = lean condition ... air leak, crank seal, carb gummed up

shrubitup, on 12 June 2012 - 06:28 PM, said:

Thanks for putting your time and energy into trying to help me on this!  I filled up a pretty big pickle jar that took a good 30 seconds or longer, all with the same smooth fuel flow rate from the fuel line (disconnected from the carb and routed into the pickle jar, lol).  So I'd say that I don't have a clog there...

terrobelone, on 12 June 2012 - 06:59 PM, said:

I appreciate your thoughts on this issue, thanks for taking the time to chip in.  The problem originally started with the throttle being sort of stuck not being able to close all the way.  My son got scared and killed the engine.  I got the throttle straightened out by taking it for a quick ride and "blipping" the throttle wide open and then letting off.  It returned to normal when I did that.  So all of the problems seem to have started all at once, and with a physical occurrence of that throttle sticking like that.  That's why I wonder if maybe the nozzle might have gotten slightly reamed so as to allow too much fuel to flow??

ericinmichigan, on 12 June 2012 - 08:30 PM, said:

I think it is time to ditch the mikuni and put a PWK on there.

What have you taken apart so far ?

Problem SOLVED!!

I only have my son with me every-other weekend, and I was just plain out of ideas on how to fix this thing.  I called a couple of my buddies who are mechanics and asked if they could sneak in a look if I brought it to their place some evening, but both of them are busy with other side work.  So for the first time, I broke down an brought it into the dealer where I know the guys and buy all of my parts.

I dropped it off late yesterday, and just got a call from them - they said it's the kill switch wiring.  Apparently it frayed and when the bars get turned one way, a wire rubbed against the frame.  $44 is way less than I was afraid of, and I'm really glad that the dealer was kind enough to understand my part-time parenting situation and get the bike right in.

Thank you to everyone who chipped in thoughts.  It's quite a coincidence that this kill switch problem reared it's head right when the carb issue happened, but that's the way it goes sometimes I suppose!  Thanks again!!

Eric