Research

The following are links to various forums where the performance, specifically the top speed, of the sh50 Yamaha Razz is discussed.

http://www.provoscooter.com/vbull/showthread.php?t=9677&page=4&pp=35

http://www.scooterinvasion.net/forum/viewtopic.php?t=270

http://www.provoscooter.com/vbull/article.php?a=29

http://www.provoscooter.com/vbull/showthread.php?p=94383#post94383

http://www.provoscooter.com/vbull/showthread.php?t=9248

http://www.provoscooter.com/vbull/showthread.php?t=8612&page=3

http://www.mopedarmy.com/forums/discuss/7/26326/26312/

In one of the provoscooter links, the existence of the CDI limiter is discussed. I lean more toward the solution proposed in the mopedarmy link. If the CDI was the problem, all Razz owners would experience the same top speed problems. Instead, there are mixed reports on top speeds of optimal condition Razz’s with minor modifications.


The last link, to mopedarmy, is what I believe to be the closest and realistic solution to fixing the top speed issue. The post seems to suggest that there is either no CDI limitation, and it is merely an issue of an underpowered engine coupled with a single speed chain drive. Perhaps an insufficient CDI is partly responsible for the Razz’s underpowered nature.

Out of all the research I've found, this makes the most sense. This supports why nitro methane would have an effect on the top speed. It simply makes the engine work harder and turn more RPM's. This would also validate a few provoscooter member's claims of high speeds. Maybe the top speed limitation is a combination the underpowered nature of the engine and the low geared set up of the chain drive system?

I have decided to test the information in the mopedarmy forum. Instead of different clutch springs, the factory air box, and a fabricated exhaust system, I will use a 17mm K&N style dry flow air filter, the factory exhaust with four 1/4 inch holes drilled into the back of the muffler. I will also opt for a larger carburetor. If this is successful, I may reach speeds in the low to mid 40mph range.

This is all, of course, no more than simple hypothesizing. I think the case of the Chinese Razz clone, the Qingqi Kasea 50b should also be looked into. According to one of the links above, it is an exact clone of the Razz except that it can achieve speeds of 40-50mph. If this is true, then perhaps pullies and a CDI more friendly to high speeds are a direct swap to the Razz.
Also discussed are the CDI boxes from the Yamaha Blaster and Marshin Predator. I have not been able to find any conclusive information on the Marshin Predator, I believe it to be another Chinese bike, more than likely not a Razz copy. The pictures I have attached show the CDI’s from the Predator and the Razz. In appearance they are the same. If I can find a dealer or parts carrier I will also try the Predator CDI. Perhaps the Chinese retro adapted a Yamaha design CDI on their bike. This would support the claims of the Yamaha Blaster CDI appearing the same as the Razz.