Vintage Dirt Bike Q & A

hi I know this is honda world I have 2 75s &a79 250 But this ? is about a 82rm125 i bought.I figure it may have an issue someone has seen b4
im getting oil in the carb running out the overflow.Bike starts easy runs okay .no oil in air cleaner! crankseal ? reed? but why in carb overflow and bike starts easily and seems to be okay.Any help appreciated.Thanks

I can't imagine that bike has an overfilled crankcase and a crankcase vent tube running up into the airbox somewhere. That would be way too street-bike nerdy for a dirt bike.

You've got to mean that you have fuel coming out of the carb overflow. Premix sure, but with fuel in it. Are you seeing an oil slick on the ground? Maybe there is so much premix flowing out that after the gas dries up it still leaves a glaze of oil on the ground.

Bottom line: You probably have fuel entering the carb when it's not suppossed to. Check the whole system from the petcock to the fuel inlet needle and seat to the float level.

The petcock will have an old dried up rubber washer thingy inside it. Search ebay for "fuel petcock gasket" and get a new one. There's a guy up in Canada that stocks tons of them. I wish I knew of somebody closer.

The fuel inlet needle and seat can be checked by taking the float bowl off, holding the carb upright, then blowing on a newly installed (not nasty tasting!) length of fuel line. When you lightly (very lightly, no harder that if they were floating in a bowl of fuel) push the floats up toward the carb body the airflow should be cut off with none seeping through. Likely issues include not just the needle/seat contact area, but also a rubber o-ring around the whole seat where it fits into the carb body. After 20 some years that o-ring will harden and pass gas, just like.... well nevermind.

There's a quick check to see if your float level is okay. The float should just begin to compress the needle spring when the float arms are parallel with the float bowl surface. If you have to push the floats up really high to get the needle and seat to seal, then you will have your cause of fuel coming out the overflow righ there. Just bend the adjustment tab to bring the closing point back where the float arms are parallel with the float bowl surface.

If that doesn't cover it, then throw it all out and buy an Elsinore.

Enjoy,
Jon

Hi thanks for the reply.But its oil.I have the ? because it is so unusual.I am an auto mechanic and have been pulling bikes apart for 20+yrs
I've asked my other rider friends and nobody knows.I can't figure out how its getting into the carb?

Is it engine oil or 2-T oil?
How much? Just a drop, or dripping out?

If it is 2-T oil from the mix, and just a drop after sitting for a few days, I'd say that it is normal. I have seen this sometimes on many old bikes. The fuel vapour pressure pushes the fuel up the tube when shut off hot, the fuel evaporates, but the oil stays and creeps out, down the overflow tube.
Try turning the hose and securing it in a "U" upwards, higher than the fuel in the carb. If you can see oil still pushing out, there is another problem.

There are only two possible sources:
The transmission is overfull and is pumping oil out of the transmission vent up into the airbox then it's running into the carb. Check the engine cases for a small diameter tube that runs from the top of the transmission case area. If that tube's other end is in the airbox then you might have found your oil source. Check the manual for the bike and see how much oil it should have in the transmission. Most two stroke dirt bike require well under 1 US quart.
The other only place it could come from is oil settling out of the premix. Most modern oils stay suspended pretty well in gasoline mix. Others can settle out of the gas mix over time. Try mixing something modern in with the gas at around a 32:1 to 40:1 ratio. If you run castor oil at 15:1 you probably will see oil coming out of the overflow after the bikes been sitting.
If your fuel petcock has good seals and if your needle and seat are sound and if your float working and set correctly, you shouldn't have anything coming out of the overflow tube.
If this really is just a little drip now and again sitting at the end of the overflow tube, there's nothing odd at all about that. If your overflow line runs all the way down below the engine and is cut off at an angle, then you'd probably never even notice it.

Run it!