I have a predator 212 with a billet flywheel, a billet rod +.020 3.328, mod 2 cheater cam, 26mm nibbi carburetor 115 main jet, auto lite racing spark ar3910x plug, header exhaust, 26lb valve springs, and 10 clutch to 36 sprocket gearing, I have a monster moto mm-b80, the max I was able to achieve on a bus lane holding throttle for atleast 30 seconds on max it acts like it has a rev limiter sort of I don’t know what’s going on because it’s only going 60mph but other predator 212 stage 1 builds go 60mph I really want to know the fix as I am extremely nervous I spent all this money just to go 60mph when I take the chain off and start it up and rev to max it revs but then takes to dips down rpm’s a little I can take a video I just want to know how to fix it.
Minibike running wrong not going faster
- Thread starter Minibikeproblems
- Start date
- Tags help dont know whats wrong
I’m sorry I don’t know how to calculate my rpm’s I’m only in the basics of tuning and building not into the math of it yet and my rear tire measurements are 145/70/-6 they came very skinny tires the last pair I had were a lot wider and I’m running 4 maybe 5 psi on the back and around 9 psi on the front from 70% throttle to 100% there is no difference it doesn’t pull more and it doesnt rev up higher
Without a tach and knowing what your rpm is I can only guess. The 145 tire is 14.5 “ tall. The 10 tooth clutch and 36 tooth rear sprocket is a 3.6 to 1 ratio. The mods you did increase the rpms where the engine makes power and your gearing is preventing the engine from getting there. You should start at a 6 to 1 ratio but you need a tach to understand what is going on.you should never free rev the engine unless you want to see it explode.
That is the size designation, not measurements.
145/70-6
145 is section width in millimeters (145 mm = 5.71 in)
70 is aspect ratio in percentage (section height is 70% of section width)
145 x .70 = 101.5 (101.5 mm section height)
101.5 x 2 = 203
203 mm = 7.99 in
7.99 + 6 = 13.99" OD (tires vary and often don't match their designated size; it's best to measure the actual OD)
145/70-6
145 is section width in millimeters (145 mm = 5.71 in)
70 is aspect ratio in percentage (section height is 70% of section width)
145 x .70 = 101.5 (101.5 mm section height)
101.5 x 2 = 203
203 mm = 7.99 in
7.99 + 6 = 13.99" OD (tires vary and often don't match their designated size; it's best to measure the actual OD)
I agree with Ole, your gearing is way off; you need a much larger rear sprocket or a jackshaft.
JMO as an old fart who learned a long time ago that broken bones and 3rd degree road rash really suck, 60mph on something designed for a max of 23mph is too damn fast, especially on public roads. Get a motorcycle and proper riding gear.
JMO as an old fart who learned a long time ago that broken bones and 3rd degree road rash really suck, 60mph on something designed for a max of 23mph is too damn fast, especially on public roads. Get a motorcycle and proper riding gear.
Yes I don’t think it’s my gearing that’s bad because many people I know say they grab a mikuni and a header and 3.6:1 ratio and they clock out at 70-75mph I might try going for a 4.8:1 ratio and see what goes well the tachometer is also ok it’s way I’m going to see how much my predator tops out at with and without the chain and see if it’s power loss or there’s a different problem that may be restricting me any further from reaching that 70-80mph mark
Do you also think arc racing 26lb white valve springs would be ok or maybe the fix? I saw someone else in here that said they had the same problem at me but then they bought valve shims but I don’t have that much money to be spending so I’m wondering if I can use the white 26lb valve springs with stock valves and retainers?