In October of 2008 I traded my '01 Gas Gas XC300 for this M206 Mk11 Pursang.
Despite the ongoing saga with the Sherpina I was somehow drawn to add a second Bultaco to my stable. My background has been in racing enduros and while I believe trials can help anyone become a better rider it certainly didn't fulfill my need for speed. So I had the bright idea to get into vintage motocross. In a round about way I ended up trading my 2001 Gas Gas XC300 to my friend Mark B. for his M206 Mk11 250 Pursang. The Pursang, with it's long travel, relatively speaking, suspension is actually a post-vintage motocross bike. It also had the standard left-side shift/right-side rear brake which would save me from possible disaster in a panic situation.
Mark rode the Pursang at the 2007 SMOG East Trail Ride.
I was quite familiar with this bike and knew most of its recent history. Mark had campaigned it in the AHRMA Northeast Post-Vintage class, but had a number of problems with the bike. For 2008 he switched to a Maico 400 to campaign in the Vintage class. I spoke with SMOG Grand Poobah, Ken Mcguire, who actually built the motor in the Pursang. His comments led me to believe the motor was solid and it just needed some minor tweaking to get running reliably. More than one person warned me that Mark's mechanical skills are somewhat questionable. Still my Gas Gas needed some work as well and resale on a seven-year-old Gas Gas is pretty poor. I actually considered it a fair trade, as did Mark.
Mark racing the Pursang at Broome-Tioga in 2007. He's a bit big for a 250.
I test rode the Pursang at the '08 SMOG ride and right off the bat I could tell the jetting was way off. The motor would barely idle and would die once you let off the gas unless the choke was on. It also would stumble just off idle, but ran very lean in the top of the RPM range. The Pursang had a Mikuni carburetor installed by Mark with a K&N air filter. Additionally the fuel lines from the tank to the carburetor resembled a spaghetti factory with an inline Fram automotive fuel filter. The Mk11 was the first Pursang to use a "high-pipe" expansion chamber. On previous Pursang models the expansion chamber ran underneath the frame where it was more prone to damage. To facilitate using a "high-pipe" the fuel outlet on the left side of the tank is angled away from the pipe and an inline fuel tap was used. Mark obviously did not give much thought to plumbing the fuel lines.
The Pursang looks right at home in the garage, sandwiched between my '03 Gas Gas EC300 and Sherpina.
It took me a week and about $15 for some 1/4" fuel line and an inline filter, but I got the fuel lines plumbed correctly. Next I spoke with Tim Weaver at Bultaco Motorcycles, who gave me some approximate jetting specifications. Since Mark had left the stock jets in the Mikuni I went ahead and ordered the correct ones from Tim as well as a few larger main jets to compensate for the free-flowing K&N air filter. I also went ahead and cleaned/re-oiled the air filter as it appeared to have been a while since this was last done. Along the way I noticed the spark plug was an NGK B7ES, one step hotter than the recommended NGK B8ES, so I swapped it out for the correct (heat range) spark plug. In addition to this I also changed the primary oil, transmission oil, fork oil and dumped the leftover premix in the tank. I mixed up a fresh batch of premix using 92 octane pump fuel and Castrol 2T two-stroke oil at a ratio of 32:1. It took me a few runs, but I got the jetting dialed in fairly spot-on. As suspected I had to go up two sizes on the main jet, but the motor pulled clean from idle all the way up to the top of the RPM range.
