Ok I've changed my jets and almost narrowed it down to whats best. 95 is golden. Trying 98 and 100 main tomorrow. I also cut the skirt of the piston at TDC so it could get more gas. Gained 2-4 extra mph now it does 35mph at most. I've seen in other posts about widening the exhaust port will benefit my motor greatly. Question tho, how much do I need to cut? Someone on YouTube said about 2mm from both sides, top and bottom. I think that's a little to much. I've already ordered a new cylinder just in case I mess it up. This will be my first time doing this
Jetting a 21mm pwk carb at 164ft above sea level?
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ive cut around 4mm form the top and around 1mm from each side. these engines have very little exhaust port duration (around 135) and you want at least 165 for general use, you can cut a lot out but if you go too far, you can ruin a cylinder, id get a degree wheel and measure what you have, and cut accordingly, a digital caliper is a very useful tool as well. (becareful!! this takes around 3hrs, so don't rush the bit, and go in baby steps!)
also, the size of the port is not really important, the angles of the port is more important.
clean all the ports first, then see what you want out of it.
good luck, and cant wait to see the build!
FNTPuck
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With the 21mm OKO drilling a 1mm hole into the circle boss right at the "D" when looking at it from the bottom with the bowl off helps tuning a lot with these tiny engines.
Basically widen ports, match the transfers to the case, run a good carb (VM18 or PHBG 19mm is fine for most stock bore builds, OKO21 works but a bit overkill unless youre a big bore or Frank), and an expansion pipe. The tune is everything, most people don't jet properly.
My chinagirl does 53mph without anything expensive.
Basically widen ports, match the transfers to the case, run a good carb (VM18 or PHBG 19mm is fine for most stock bore builds, OKO21 works but a bit overkill unless youre a big bore or Frank), and an expansion pipe. The tune is everything, most people don't jet properly.
bike4life
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what kinda of speeds would you guess of a predator 212 bike with governor removed? 70mph then???
FNTPuck
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Very simplified:
55-60 but it gets there WAY faster than a chinagirl. Valves begin floating around 4500 but doesn't hit full on valve float until around 5k when new. As it gets miles and the springs wear, it acts as a limiter and starts dropping down to 4900, 4800, etc. No internal gearing means that even with all that TQ, you are kind of limited in gearing choice so you need to run a proper jackshaft or tq converter.
Very different motors...10k+ rpms from 70cc can get nice top end, but will still be slow from a dig. A 212 is a monster from a dig, but the low rpm limits your top speed until you start spending money on cam, port work, valvesprings, etc. Can't just go tiny rear sprocket because then you get clutch chatter and surging down low and can ruin parts.
Many people do it but I wouldn't remove the gov without at minimum billet flywheel and HD valvesprings. We're talking like $120 for not only more performance and 6-6500rpm capability, but also safety - a flywheel letting go at 5,000rpm is moving at over 150mph and can literally kill you. Now I think they are bolted in, but on older clones the timing magnet would launch out of the flywheel as well.
If it will see over 5-6k often than I would change the rod too for insurance...starts getting expensive pretty quickly.
For 212 and up 4stroke info I would skip the motorized bicycle pages and look at gokart performance sites. They have been using and abusing those motors for YEARS before the MB guys started and know all of their pros and cons inside and out.
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id try some blue locktite, and id CC that cyilderhead, as chances are that it's a 8cc low compression head.
So a better head would be best? Any recommendations?
a genuine fred head 6cc is the best, stock head is good,
a 8cc one is good for cooling, but horrible for performance. .
Yeah it does stay pretty cool. The pipe is even touchable after riding. So the stock would be better than the one I have lol thats crazy. Wished I'd asked before buying this one lol
