Vintage Dirt Bike Q & A

What carb have I got? in the parts catalogue it appears to be different for an MT250 I need parts for it but first I have to figure out what it is.
also what does the brass pipe on the float bowl do?? someones home made the brass needle, not sure if it works....

Anyone?

It is an MT carb. I have three, two on bikes and partial bought off eBay. Two of the 3 have the casting line like yours around the slide housing.

The tube in the float bowl is for overflow. There are two on the carb body <brass fitting pointing down on your pict> that vent to the air to equalize pressure. One of the two may just have a rubber plug on it.

The bottom brass fitting is just to drain the carb when you have a bit of water in it or want to get rid of any residue.

The MT took a special idle screw with a hole in it. If that is what the previous owner replaced, you may have trouble getting it to idle right.

Thanks, what parts should I buy to over haul the carb? theres a place here that I buy from in NZ, but I have to order them seperate, they dont come in a kit.

I'm bad at this. I always just get used carbs off eBay when I have a problem. Hopefully someone will jump in where I am wrong.

If you have the slide and top, try to find a "Keyster" rebuild kit. They are the most complete and have the most parts like float needle valve and seat. I think most even come with new jets.

My Haynes manual only lists the carb as Keihin type PW. I looked at two carbs and they both used a #58 slow jet. One had a #100 and the other a #115 main jet.

There should be some numbers stamped on the carb just below the choke lever pivot. The carb that looks like yours has
0040
BMK7
Stamped on it and the other has
0040
BNG7
Now this is where I get lost. I thought the stampings referred to the jetting and slide. That is the 0040 => a #40 slow jet. Since neither carb has a #40 slow jet and I am pretty sure the one I haven't looked at is a #58 too, I obviously don't know how to decode the numbers right. Maybe your suppier can give you some insight if no one here can.

This page might help out. It looks like the PE carbs are the closest to what you have in the picture.

http://www.sudco.com/keihin.html

...and jets:

http://www.sudco.com/keihinjets.html

...and on-line catalog:

http://www.sudco.com/cat32/127-128.pdf

...and a Mikuni alternative:

http://www.sudco.com/cat32/45-51.pdf

You can buy the whole carb from them I believe.