The "680" or as some people call it, the "686," is an easy and dependable update. All you do is bore 2mm oversize and install the 102mm Ross or J&E piston. Obviously, you will want to port it, add a cam and clutch springs but you do not need to split the cases.

Going to the 105mm you will need to replace the sleeve and bore the engine case. This is very invloved as you must remove the entire engine and perform a complete dis.

For the $$ and time, most people will be very very happy with the 102mm. I can honestly say that the 105mm with either the stock stroke or a 88mm stroke is for serious drag racing. There are no hills on this planet that the 102 will not climb as fast as a Banshee, built LT500, any 330R, DS, etc. I have put hundreds of hours on the 102 and never had a problem.

I have yet to completely test the 105 with stock and +4mm stroke. What I have noticed is that it is way more power than most people will every need or use.

 

To answer all your questions, " I don't know." Dynojet does not jet and Dyno quads as part of there moneymaking business. They do research and developement, and then market there products as Dynojet jet kits. They did mine for me as a research project. He did say that the jets used were regular Dynojet jets. He just found the right combination that worked best for my bike.I wasn't there when he did the jetting, so I don't know how many times he tried. I will ask these questions next time I talk to Mike. As for 42HP being low, I am at 2500 ft above sea level. I am VERY happy as to the results. Throttle response has definitely improved, and the power is there in every gear.