30 BHP Blog

The new port map looked like this:

As stated earlier, the ports were done very oval. Later that year the GP made it to the Lambretta Euro in Spain with out any issues, at the start of that rally I started using a cheaper 2 stroke oil, Rock oil groundsman. Its about a quarter of the price of Rock oil Synthesis which I was using and the spec of the oil looked good enough for an old Italian shopping bike.
The oil spec meets API TC, TD JASO FA, FB, FC GLOBAL ISO-E-GB, GC,GD

However on the way home from Cleethropes later that year, the scooter started running badly, no mater how I jetted the Mikuni it just ran very rich to the point of four stroking. When I got home I tried a fiends Mikuni to see if the problem was with the carb, it turned out that it was, with the newer Mikuni with the same set up the engine ran well but with mine it ran rich, I came to the conclusion that the fixed atomiser had worn so I looked around the Internet for another carb. I kept reading about bikers who were changing their Mikuni’s for Keihin Airstriker’s so I decided to get one to see how it would run.
Just before the Run to the Hills it arrived with the various jets and needles I had ordered, As no one was using these carbs on Lambretta’s to my knowledge I had no idea where to start with the jetting. With all jetting you start with the pilot, get a good tick over that drops down quick, however with this carb, no mater what I did with the pilot jet it just wouldn’t tick over. Instead it would just cut out as though the pilot was too rich, the air-screw had no effect at all with any of the jets I had, when I phoned up to get some smaller pilots I was told that I had the smallest one already in my arsenal. This left me a bit stumped. I decided to make the cut away in the slide larger to see if this would help, it did but I had to cut it very steep so I ordered the weakest slide which is a number 7. I ended up with a set up that I could ride with but was far from right.
The scooter made it to the Run to the Hills and ran quite well on the way home.

its next outing was IoW in August, we set out from Birmingham late on Saturday afternoon because of work commitments and while ridding on very little throttle due to a slipping clutch it heat seized solid so we got recovered home. next day I took it apart and saw it had been running very weak at that throttle position with the new carb. Obviously the small pilot I had used to get it to tick over wasn’t supplying enough fuel. The piston was ruined so I had to buy a new one.

This time I decided to buy the Wossner version of the H2 piston, it’s a lot lighter than the Wiseco, its Teflon coated and it has cut outs either side above the gudgeon pin. I had to do the same mods to the skirts but the ring pegs are in the same place as the Wiseco so there is no need to re-peg.