Are you talking about the left pipe or the right pipe?
FWIW, from the colors I thought the bike might be a Greeves, but could not find any Greeves to match.
I had a '73 TM250 back in the day. I always thought the great dirt bike technology revolution happened between say '73 and '78, with the evolution of long travel suspension. The pic of the '68 makes me realize that alot changed between '68 and '73 as well.
I was told its a 1967 Suzuki. I didn't get the model, but was told it was one of 300 made and only 1 of 20 know to exist today. The bike was provided by Donnell Cycle out of Independence, MO. Out of all the vintage bikes at the reunion I attended, it was the most talked about one of the bunch.
The next machine is a 1968 Suzuki TM250. In 1965, Suzuki sent an engineer and one of the factory road racers to Europe to test and develop a motocross bike. A single cylinder and a twin cylinder machine were tested and they soon decided to concentrate on the single cylinder model. It's important to note that Suzuki was the first Japanese company to build a motocross machine. The first machine, the RH66 stole many ideas from the CZ250 Twin Port as did the 1967 RH67 which was somewhat refined from the 66 model. The Europeans laughed at the early combination of a poorly copied CZ and a road racer attempting to compete in the 250 GP's.
This would change in late 1967 when Suzuki hired Ollie Pettersson to develop the bike and later Joel Robert and Roger DeCoster to race the significantly improved machines. The TM250 is based off of the RH67. This model is the first production Japanese motocrosser and only 200 were produced World-wide, with the US getting 65 in early 1968. The bikes were sold with a parts kit that included a rod kit, pistons and rings, replacement clutch parts, gearing and other items. The American Suzuki distributor hired Gary Conrad, Preston Petty, and Walt Axthelm as riders to showcase the new machine.
The early TM250 was hampered by it's heavy weight (235 lbs), peaky power, and poor handling - not to mention the heat that was transferred to the riders bottoms from the twin pipes. This machine is one of my top 3 favorites in the collection. An excellent restoration by my friend Chris Carter of Motion Pro and it being extremely rare, make it very special to me. I can't tell you how excited I was when Chris and offered to sell me this motorcycle.
I took a look at the magazine test. Dyno charts, 1/8 mile drag times with mph, etc... Somethings (like motorcycles) sure have improved in the last 40 years. Not sure I can say the same for dirt bike magazines.