48cc 2 stroke bogs and vibes

G

graydog8josh

Member
I have a 48cc china that is bogging at 1/4 throttle and vibrating really hard at hi rpm. ive opened the ports a little and trimmed the skirt on the intake side but nothing too extreme. Im running a puch jammy pipe from treats and the sha 16.16 carb with a 65 jet and the 50cc hi comp puch head. anyone have any experience with slide tuning?
 
you may need to play with the emulsifier tube in your carb to get it running well at low end. you may need to widen the lower hole or add a third hole
linky
that link covers some good basics about this kind of carb, talks about slide tuning a little and talks about the emulsifier tube too. a couple of good links in there as well.

as for the vibrations the first thing you should do is double check your motor mounting. some decent advice I have heard on here "grab your bike with one hand and the head of the engine with the other and try to pull them apart, if you get any movement at all your engine needs to be held in better."
 
yeah my jetting is too lean for one, i went up from .65 jet to a 68 and still running hot, might go to a 72 jet. I also used a really tiny 1/32 drill bit and opened up the bottom emulisifier hole. I also am in the process of making my own rear motor mount to fit my seat tube 1.015625 made of solid aluminum.
 
I also am getting a reed block maybe that will help out bottom end power. Wondering if anyone else is trying a mikuni on the 48cc's with mild mods
 
lots of people do mikunis and reed valves, but do that is less of a "bolt on" upgrade and more of a "now I can cut away half of the piston skirt, and rebuild the porting from the ground up for a race mtor" upgrade.

a longer intake is a more entry level upgrade for low end power. also the SHA carb is not a bad carb at all (sometimes needs some tuning though) you should be able to get your engine pulling hard without too much modification.

also if your mounting is even slightly loose that will screw you over more than not having power.
 
Yeah, i was def too lean went up from a 65 jet to a 72 jet over the last couple of days. Now its 4 stroking for a few minutes on top but its much more responsive on low end then when it gets hot its not four stroking anymore. I was hoping that the reeds would make it even stronger on low and mid range because this bike ive geared low to try to get it to pull wheelies.
 
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