catraprez (catraprez) wrote in bike_shop,

Latest Project

For the last year or so a couple friends of mine have been trying to get me involved in vintage motocross. Of course not having a vintage-legal motocross bike has been my biggest deterrent. Well that and my experience racing motocross, back in 1990, was less than pleasurable after I crashed my brains out attempting to clear a double (jump).

All fears aside, vintage motocross is more inline with what motocross racing was like back in the 70s, due to the lack of suspension, and less about catching *sick* air. That still leaves the bike problem. Then, a couple weeks ago, my buddy Marc let me borrow one of his vintage MX bikes. The bike is an M-206 Bultaco Mk11 250 Pursang that he raced back in 2007. As you can see in the first pic below, Marc is kind of big to be on a 250 and he moved up to a 400 Maico for 2008.

Marc racing the Pursang at the 2007 Binghamton Vintage MX.

After a quick ride I reluctantly (yeah right, who am I kidding?) loaded the Pursang in my pickup and brought it home to give it a better look. Mechanically the motor has 5 hours on it after a complete rebuild (new piston, rings, con rod, bearings and seals). It also has a new Motoplat electronic ignition and a new Mikuni 36mm carburetor. Cosmetically it needs quite a bit of work to be a *museum* piece. While that's not my intention, I do like my bikes to look as good as they run.

Whats this, another Bultaco?

Even though no money has exchanged hands, once I got it home I started going through it. A WOT plug reading indicated the Pursang was running lean on the main jet. So I took the carburetor apart and got all the numbers off the jets. While I was down there I pulled the K&N air filter, cleaned and re-oiled it. Then I re-plumbed the fuel lines running from the tank to the carburetor and replaced the single automotive-style fuel filter with two motorcycle fuel filters. The fuel tank straddles the backbone of the frame and, unlike my Sherpa-T tank, does not have a balance hose between the two sides. There are two fuel lines coming from the tank to the carburetor. In the process of re-plumbing the fuel lines I discovered the right-side petcock was leaking due to a bad seal. Luckily I had a spare petcock that I put on. The sparkplug was one step hotter (NGK B7ES), so I installed a B8ES plug. Then I called Tim Weaver at Bultaco Motorcycles (formerly Hugh's Bultaco) and got their jetting specs for this application. The advice was free, but rather than being a moocher I went ahead and ordered the jets from Bultaco. The silencer has probably never been re-packed so I need to figure out how to take it apart or mount up a universal (re-packable) silencer. Finally I replaced the el-cheapo kill button with a better one I had on hand and re-wired it. Now I need to mix up a fresh batch of premix and take it out for some WOT plug readings.

What a pristine M-206 Pursang should look like.

As far as the cosmetic stuff goes I can put up with the frame being powdercoated the wrong shade of blue. At some point the plastic aftermarket side panels were hacked apart. Replacements are $50/side, so I'll be hitting up e(vil)-bay for some used ones. The fiberglass fuel tank has been sealed so it doesn't leak or bleed through, but it needs new paint, badges and decals. Mostly the bike just needs a good thorough cleaning, but before that I'll probably go through the suspension first. Over the years I've discovered it doesn't matter how much power your bike makes or how nice it looks if it rides like crap. The best modification you can do to any bike is tuning the suspension to your taste.
  • Post a new comment


    default userpic

    Your reply will be screened

    Your IP address will be recorded 

    When you submit the form an invisible reCAPTCHA check will be performed.
    You must follow the Privacy Policy and Google Terms of use.