GPS speedo wrong or am I going insane?

[DaPope]

Original gearing
12 tooth on torque converter 72 tooth on rear. 15 inch tires

New gearing
15 tooth on torque converter 60 on rear. 15 tires

Top speed on both is 44mph. Tested repeatedly on same stretch of road. I knew I wasnt going to spin to the same RPM, or at least was hoping not to but it for sure got up there, Tested with gps speedometer by Cool Niks.

So can someone help me out? Is the gps speedo wrong or did i really just go from spinning 6k down to 4k rpms?


I mean on the bright side, I quelled its desire to wheelie from a dead stop.

 

[Kyminibiker]

not enough motor to overcome wind resistance is my immediate guess. what engine? I am gonna try a 15t/54t with a stock 212 on mt thunderbird, I weigh about 205. I plan to mod the 212 a good bit but still curious what the stock 212 will do when I run it.

 

[DaPope]

modded briggs 6.5hp ohv. i figured wind resistence would stop me from hitting the supposed 60 plus that the gearing said was possible but literally the same exact top speed has me questioning.

 

[Kyminibiker]

if all things check out like fuel, spark etc, might just be a brick wall that takes more power to bust through. Could be luggin the motor with those higher gears. Might need the deeper gears to keep it in the cams powerband. could be a lot of thiungs without knowin all variables its tough, but I did take a edumacated guess at it lol

 

[DaPope]

im thinking tomorrow Im going to throw the 72 back on the rear and try again. the mikuni was leaning out on the top end, and seems to be again which made me think the rpm were similar. guess tuning that a bit better will be first, then try the 72.

 

[Kyminibiker]

im thinking tomorrow Im going to throw the 72 back on the rear and try again. the mikuni was leaning out on the top end, and seems to be again which made me think the rpm were similar. guess tuning that a bit better will be first, then try the 72.

yea fatten her up and see what happens, you might be surprised.

 

[DaPope]

Sorry for the delay. Throttle got stuck wide open on a start and snapped the twist connector. Just got a new one in.

Getting the 72 back on was tight but now it is good. Will need to tighten the chain before riding more. Typing on a break. Just set a top speed of 51mph and it wasn't at full throttle. I'm think I need bigger jets as full throttle begins to bog her. But at this point I have no idea what is going on and could use help.

To recap
12/72 top speed 44 mph
15/60 top speed 44 mph
15/72 top speed 51 mph


For now I'm keeping the 72 on the rear. And I guess will order jets in a few weeks.