new guy greetings

[sawracer]

Hello all. Nice forum, much appreciated. Im a long time gearhead. I own an 05 zuma, a 61 vespa vbb 150, and an ancient honda elite 80 4 stroke. The honda is boring but i keep it around because its reliable and was a gift. I picked up the zuma and left it stock for about a month. I added a contessa cylinder, leo vince pipe, carbon reeds, upgear kit, athena variator, and athena crank. I destroyed the original crank using an impact to install the variator. (thrashed the splines due to misalignment). Rats. I then scrapped the oil injection in my divine wisdom and holed the piston due to a haphazard fuel mix. ( too much oil?). I then got to tear it down to parade rest once again to clean out the piston parts, and install a new piston. I'm now back on the road using it as a commuter for a 32 mile round trip here in sunny socal. 51 mph gps is my current best and I'm shooting for a solid 60 mph.

[Blackbomber]

Welcome, and good luck on hitting the MPH mark. Yes, too much oil in the premix could have been your problem. Technically the problem was caused by pre-ignition. Pre ignition is the fuel mixture being ignited by a hot spot in the chamber (as opposed to the spark plug). This is most often caused by lean mixture. The more oil in your premix, the less gasoline you are getting. For instance, if you go from straight gasoline to a 32 to 1 premix, you are effectively reducing the fuel available to the carb by 1/32nd or roughly 3%. Obviously differing oil ratios alter the effect accordingly. Let this be a lesson to us to always double check our jetting after converting from injection to premix.

The one thing I'm unclear on is whether all jetting needs to be increased, or whether one only needs to worry about the main jet size. My guess is that in theory this affects the mixture equally at all throttle positions, thereby theoretically requiring jetting alterations across the board. In the real world, however, I think upping the main jet is probably sufficient. Anyone who knows the right answer, please share.