Vintage Dirt Bike Q & A

Should also ask if you did anything with the carb or if it still idling at red line?

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74 MT-250
06 Husky TE-450

I will leave the oil pump alone for now. After I get the idle fixed, I'll drive it around and see how it goes, if Im fouling plugs often or what. I havent touched the carb yet, that is next on my list, and Im hoping that cures the idle problem. I dont think the idle is related to the left side crank seal, because there is no fuel oil mix anywhere on that side, its dry.

Hi candt,
I am going to give you my two cents on your RPM & smoking problem. It sounds like an air leak!! I had a very similar problem on my 73 CR. Once every so often it would start reving to the moon. After doing this on and off for awhile it started to smoke more and the reving became more frequent. I decided to finaly fix it. What i found was that the gasket between the two center cases had rotted. That allowed air and oil from the gearbox to enter into the crank case.
Now If the previous owner leaned the oil pump out because it was smoking bad. And was having the same trouble with the RPMs? It could be a similar problem?

Or it could be the oil seal on the clutch cover side?

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W.F.O. All the way!

Can you give us a little history on the bike like how long it has been sitting? How it was running before it was put away? Letting a bike sit especially without fluids can cause seals and gaskets to dry up. Warm dry climates probably add to the problem. Loren posted instruction on building a leak down testing devise that would confirm the problem. You can search the knowledgebase for it.

If the bike has been sitting for a couple of years you may need to dismantle and clean the carb.

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74 MT-250
06 Husky TE-450

Elsinore, thanks for those suggestions. That is something I will be checking out.

I think the bike has been sitting for several years. The guy I bought it from, purchased it from the original owner. The guy I bought it from only had it a few months....he purchased it with plans to restore it, but didnt have the time, so I purchased it from him. When I got it, it had fluids in it, oil, trans oil, gas. But most likely the carb is gummed up. I know the bike has lived its entire life in Wisconsin. My dad and I did a compression test on it, and it read 125 lbs. As for how the bike ran before it was put away, I have no idea. Im tempted to bypass the oil pump and premix the oil and gas right in the tank, so I know I am getting the correct amount of oil to the engine. Thanks for all of the help, I definately have my work cut out for me this winter.

An update....today I took apart the carb and cleaned it out (it wasnt that dirty). I put it back in the bike, and got it running, and about 20 seconds later it died....the plug had fouled. During the 20 seconds it was running, it sounded good, but I have no idea if the revving problem is fixed or not, would like to have it running longer than that to come to a conclusion. The bike has been fouling plugs a lot, and my first thought is the crankshaft seal on the clutch side, but the bike doesnt smoke that bad. But I dont know what else would be causing the fouling of the plugs?

When you cleaned the carb did you make sure all the passageways were clear or did you just clean the float bowl? If the air way to the slow jet and mixture screw is plugged it will run rich. There is also an airway to the needle jet seat that can plug. Both passageways start at the air filter end. You must remove the main jet, bend down the locking device and remove the seat to access. A rich carb will certainly foul plugs. If you have a compressor you can blow out with a basketball inflator.

Did it run well with all the jets you are using now? The only things you want to change in a rebuild are the gasket, o-rings and the main metering valve for the float. Do not use steel wool on the needle.

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74 MT-250
06 Husky TE-450

When I took the carb apart, I cleaned out the float bowl, and blew out the passageways. I didnt take the seat out, because I didnt see a way to get it out. It looks like its pressed into the carb body. I took out all the jets, and blew them out. One thing I noticed is that one of the screws (not sure if it was the idle speed or idle mixture screw) was screwed all the way in. The other screw (this one had a spring on it) was about 1 full turn from being fully closed. This may have something to do with it?

When the bike runs, it does seem to run fine with these jets in it.

The piece that I refer to as the seat screws in from the float side. It screws into the piece that is pressed in. There is actual a space between the id of the pressed piece and the od of the area that I refer to as the seat. One of the holes on the air filter inlet leads to that space.

The screw that stops the slide is for setting the RPM. The screw with the internal spring is for setting the mixture. 1 to 1 1/2 turns is about right. Turning the screw clockwise restricts the air and will make it burn richer.

You may also want to check the clip setting on the needle. The middle of 5 settings is a good place to start. Also when putting the needle back in the slide the clip must be underneath the plate to hold the needle in place. If it is assembled incorrectly the needle can slide up and burn richer.

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74 MT-250
06 Husky TE-450

After a bit of research, I have figured out that it was the mixture screw that was in all the way. I will back this one out. I will check the clip on the needle like you suggested, although I didnt mess with the slide or clip at all, so it is probably where it was set from the factory. Thanks for the suggestions.