Vintage Dirt Bike Q & A

Hey this is my first post on this site so I'd like I'd like to say hello. Also I have a question about my mt250 I inherited. So a little back story it had been sitting for roughly 25 years before I got it. I ended up taking the carb apart and cleaning it like crazy and did some other work on it and it has been running perfectly for the past 4 or 5 weeks until yesterday I was running it and out of nowhere it started dumping fuel out of what I thought was the bowl drain but I'm thinking now it is some sort of over flow. I have tested the floats and they seem to be working like they should but its still dumping fuel. Is this a known issue? And is there any good place to start looking? Thanks in advance.

I got rid of my stock carb a long time ago so I dont know for sure if its a vent hose or a drain hose. If its got a screw next to it then its a drain line and the screws come loose. If not its going to be a vent tube and the floats are not working as they should. Its dosnt take a whole lot to make the float stay open and gas to come out the vent on the bowl.

Thank you for your reply I got it fixed. There must have been something blocking the float from closing completely. There are many other things I am working on for this bike trying to get it back on the road and if anyone could help give me suggestions I'd love the help. This bikes been sitting since 87 so there's a ton of work most I can figure out but one thing I'm not sure of is both the speedo and tach seem to be sticky or something because they move very slowly and will randomly get stuck is this something I can't take apart and lubricate or do they need replaced thanks a ton.

Try warming the speedo and tach up with a gentle heat source, like a small space heater a few feet away. Sometimes the grease inside gets really hard, and the heat can soften it up just enough to move it out of the way by using the cable and a variable-speed drill. I would NOT use the drill cold, as some of these instruments have clutches or similar inside to deal with jammed gears etc, and something could start slipping.

You could also heat up some penetrating oil and put a few drops at a time down into the cable entry, let it work for a while in front of the heater, then spin it a bit.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

There is a good article in the VJMC October/November issue of their magazine showing how to lube speedometer guages. Apparently, the bushings inside the speedo are often impregnated with oil and can dry out over time. He recommends using an armour chili can, setting the speedo on the side, setting it on a candle warmer, and filling the can with 10w40 until it covers the entire stem up to the bottom flap. You leave it for an entire day so the bushing warms up and the oil saturates into it. Shut it off, then pour the oil back, and let the speedo sit for another day to drain. The cooling will draw more oil into the bushing. Afterward the speedo should move freely.

They also mention an alternate issue is offered in the june/july 2014 issue.

Regarding the carb. Be sure to turn off your petcock every time you turn off the engine!!

These Kehins are notorious for dumping fuel and will fill the cylinder with gas if given a chance. (That is not terminal my any means, but it is a nuisance and a fire hazard.)

Also, make sure to empty the carb if you store it outside in the winter. While I am the only one I know to have experienced it, I had the float bowl drain tube crack. I believe it was from water/condensation expanding when it froze. Regardless, it caused the carb to constantly dump fuel when left sitting, because the float would never rise enough to stop it.

When you fixed this crack, did the leaking stop 100%? I ask because it seems like nearly all OEM MT250 carbs overflow to some degree. I've always wondered if it isn't the kickstand leaning the bike over so far.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

I ended up buying a carb on ebay and replacing the bowl. Problem was solved.

I will find some occasional drips after riding if I don't turn off the fuel prior to shutting down the motor. I attributed this to changes is barometric pressure, but it could be from leaning over.

I still make sure to turn off the petcock. I don't ever want to have to take off the muffler and use the cylinder as a sump again.