250-500cc Carb Issues...HELP

Hello guys.
Last weekend something went weird with my carb. It dumped a bunch of fuel into my air box, pipe and cylinder, and was constantly weeping out of the overflow tube...This happened while in the box of my truck.

I drained the pipe, cleaned out the air box, and pulled the plug and did change the transmission oil.
I did get the bike running again...But what i'm wondering is what happened??

Also thinking about changing the carb. and getting a Lectron- Does anyone know what model i need.

Thanks in advance.
AA

Did you check/clean your float needle/seat?

Was the petcock turned off when it was in your truck? It should be...

What carb?

Sounds like a problem with the float needle. Two possible causes: crap in the seat (as Idacurt suggested) and a worn needle, seat, and/or o-ring. To check for the former, just rotate the carb, remove the bowl, and thoroughly clean it out with carb cleaner. For the latter, you can buy a replacement set of parts from any decent carb parts place like Sudco.

My WR was dripping before an enduro this year, I rotated the carb, removed and cleaned the bowl, and had it all back together in about 15 minutes in the race parking lot, and it solved the problem. I try to replace the needle, seat, and o-ring every 5 years or so because they wear/dry out and then you're stuck with a leak until you get new parts.

Kyle asks a good question there I left my petcock on and had a similar experience
when you bump and bounce down the road fuel splashing and your carb keeps refilling itself it will end up going somewhere

Check the vent tube in the cap. Heat can cause the fuel to expand and if the vent isnt working it will push it past the needle ans seat.

To answer the easy one, Kelly (Motosportz) can get you sorted, but you'll be wanting the 38mm for a 300 if you go that route.




Also, not sure about up there, but if you had a "winter blend" gas and it was an unusually warm or sunny day for that time of year, the gas probably expanded quite a bit in the black tank. We've seen this happen down here in February/March races if the weather got too warm too early in the year -- as in while the bike was being ridden the gas would expand so much to flood out the engine if the vent clogged -- So, like Gordon said, check the vent line as well.

Stuck float can be unjammed by tapping the fuel bowl. If the fuel keeps pissing out, open the fuel cap, if it stops you have a blocked vent.

The guys are all correct, leaving the fuel on whilst transporting or in storage, will result in either gumming or pressure forced on the float valve.

Your best bet, and with any carb bike, is to practice pulling off the bowl on the bike, and giving it a blow (carry clear PVC tube), will save you heaps if you get stuck on the trail....although nothing beats pulling the carb off and giving it a blow down with a compressor.

Good Luck!!

Well it was my bad--i did leave the fuel on. And it was sitting in the sun, so it probably heated up and pressured up the system that way.
The bike is very new (2012) with low hours, so hopefully it not failed or worn parts.
Also good news, was the transmission oil didn't smell like fuel.

I did also notice that when i tip the bike over on hard angles it pisses gas threw a vent tube ...Anyones else find this, Or do i have some other issues.

Tomorrow i will tilt the carb and inspect for crud and crap in the bowl area.

THANKS for all the help guys!
AA

if you still have the stock Mikuni TMX, ditch it and buy a lectron or a Keihin PWK. Way more user friendly.

Yeah it's 100% stock.
I'll be looking into the Lectron carb for sure! Any idea the model number to upgrade to?

Honestly your best bet is to call Kelly at motosportz. The regular lectron sounds like it will give you hell to install as its too long. Kelly has some ones lectron modified for our applications plus you have someone to call if you need any help getting it dialed.

Nah, that's pretty much standard design to stop the engine from being flooded...

Heating up the fuel won't pressurize the system unless the tank's vent system is broken. Normally the vent is open and so any expansion is just relieved there.

The reason it's bad to leave the fuel on during transport is because of the bouncing/vibration. That will bounce the needle valve off the seat and let fuel into the bowl. If you're lucky, all that fuel will come out the overflow (that's why it's there), but sometimes it goes into the engine instead. On a 2-stroke this makes for hard starting, on a 4-stroke it fills the crankcase and your oil is junk.

On a 2-stroke, the transmission oil is in a separate "container" than the crankcase (where the intake, fuel, and premix oil go). If fuel in the crankcase was leaking into the transmission, you'd have big seal problems.

If it's coming out a vent tube, you have problems. However, it is probably coming out the overflow (the tube from the bottom of the bowl), and that is normal. If the float height is set wrong, it will drip out without much angle at all, so that ought to be checked, but in general that behavior is normal.

I have seen a lot of WRs with incorrect float levels as delivered, so that they drip with only a little bit of tilt, and that will also potentially mess up the jetting, so it's worth checking.

I don't aim to rain on the Lectron parade, but I'd get the jetting right on your stock carb before spending a bunch of money to upgrade, and see if it works for you. Plenty of people are happy with the TMX, it depends on your riding style, terrain, preference, and a bunch of other stuff. I ended up with a PWK on my bike, mostly because of the power delivery characteristics; it's not "better," per se, just works for my riding style. If you get it jetted right and still don't like it, then upgrade!

Well the PWK has better power delivery characteristics, isn't nearly as finicky to jet and at leaSt around here Ifor I needed a jet or something for it most motorcycle shops had them. Not saying they can't be made run decent because they can just saying a PWK is an upgrade.

I think what draws me to the Lectron is once it's set up it can deal ether with elevation changes and temp changes then either the PWK or TMX. And you can richer it up or kean It out a bit on the outside of the carb. That would be nice

Re: gas drips - yes float is too high. Bend tab toward top of carburetor some. This STOPPED my spooge issue completely. Same bike with TMX and JD kit. Works good.

Thanks for all the replies and help guys.

My jetting is bang on---I think i'll pull off the bottom of the carb and play around with the float level.