Carb Issue I Think

I'm mechanically sound, but a bit uneducated didn't own a dirt bike for 27 yrs.


2013 YZ250, runs perfect.  Bike even when cold starts on no more than the 2nd kick, when warm starts on the first kick.  Super reliable.


2 weeks ago changed oil, repacked muffler.  I don't think this is the issue, but it is a variable.


That Sat went to the trails and it wouldn't start.  Figured after a bit of kicking it flooded and put a brand new plug in.  Old plug wasn't fouled; wasn't fuel soaked, but "barely" wet.


Removed the fuel line from carb and let gas drain for a second.  Assumption:  carb is getting fuel.


Figured maybe float stuck.  Hit float bowl with screwdriver handle.  By then was ready for a break from kicking, friend took over and it started.  Ran like a champ the rest of the day - no further probs starting.


Yesterday, tough to start again - but not as tough as the first time.  Banged on the float bowl again and it started maybe 10 kicks later.  Once started, started fine rest of day.  Got it home and it wouldn't start - but it did half-ass fire a few times.  Only kicked it maybe a dozen times then put it to bed.




First thought is float is sticking, but I'm confused on why it would stick/be hard to start cold, then run fine/be easy to start when warm.


Seems like now it's tough to start when the engine is cold - even when using the choke.


If the float was indeed stuck, why would it run fine but be tough to start.  Does engine vacuum come in to play here?


I don't have a good grasp of how the carb works - is there a section/portion of the carb that just affects starting - possibly just cold starting?


Not sure how much time I'll have today to look in to this, plus tomorrow it's going in for susp work.







My guess is that your on the right track, in that it seems like it might be the float's sticking. With today's crappy pump fuel, it might have left a slight residue behind which is causing the floats to stick when the bike hasn't been ridden for a day or two. This is where I would start looking.

Thanks maniac.


Today what I did, noticed, etc.:


Removed fuel line from carb and drained almost 1 cup of fuel.  Didn't notice anything in there that didn't belong:  water, dirt, etc.  So fuel is flowing to the carb.


Removed subframe and cleaned air box/boot.  Holy hell - it was full of in almost dripping at the carb junction.  I'm actually wondering now if I'm flooding the thing.  Also noticed some "oily mess" around air boot/carb junction, and screw holding that junction wasn't tight enough for me.  Not loose, but not tight enough.  Hmmm.  Cleaned inside box/boot to near showroom condition...well almost.


Installed new/clean air filter.


Removed plug and it looked normal - normal for me as I like it a bit rich.  I change plugs every 10-15 hrs when I chng oil.


Opened throttle and things looked nice and shiny in there.  Cleaned what I could see with carb cleaner.


Noticed carb bowl drain plug wasn't tight enough for me, but wasn't leaking either.  Pulled the plug, turned on the gas, and it flowed.  Hmmm.


Put the entire enchilada back together, turned on the choke, left the throttle closed, and it fired up first kick.


I can't exactly state how I start it...I just start it.  I'm wondering if I changed my method and really just flooded the dam thing.


If so, stamp a big L on my forehead.  :lol:

Mystery problems are so much fun...

From what you've stated, specificly the amount of fuel on the airbox side joint, I'd look at the reeds to ensure they're sealing properly.

While the carb is off for that, it would be timely to take the carb apart & check the float level and inspect the jets & passages for any foreign gunk.


This will be something simple.

The problem will be in trying to not overthink it.


Good luck!

Also, remember to shut off your fuel lever when transporting a bike. The floats get jostled around in transit and then fuel might find its way into the crank area and cause a flooding issue. Here's to hoping you've got this figured out! :thumbsup:

Thanks guys.


What I need to find are videos, books, etc. to explain to me exactly how that carb works.

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