fast motor with limited drive speed?

steverpm

New Member
Jul 6, 2017
2
0
1
59
Hi - picked up a bike already assembled with a Skyhawk 66cc motor - runs pretty well, revs nicely with the clutch in but won't go over 20 mph or so, not even down steep hills. The low-end acceleration is fine and at any time I can pull the clutch in and high-rev the motor, but when it's engaged (even downhill) the motor will only rev to a certain speed and will actually slow the bike to around 20 mph from a much faster coasting speed.

Seems kind of strange - I'm told these motorized bikes don't have speed limiters....

Anyone know what could cause this?
 

steverpm

New Member
Jul 6, 2017
2
0
1
59
thanks for replying - the rear is 7.5 inches (roughly) with 44 teeth, at the motor the front sprocket has ten teeth, shown here - http://grubeeinc.com/Skyhawk Instructions.html (scroll down)

I suspect both are standard with the kit - I bought the bike used and it had been sitting for a year or so...

When I lift the rear wheel and rev the motor it all goes nice, so I can't figure out why it won't speed beyond the usual 20mph down a steep hill....
 

Ryan1977

New Member
Aug 14, 2018
1
0
1
43
I am having the same problem. Why is my new motor so slow? It's got good compression, good spark, good gas! Is my clutch plate to tight?
 

crassius

Well-Known Member
Sep 30, 2012
4,032
155
63
USA
if it is new, it may need to run in a bit - if it doesn't get better, then check compression with a gauge and read some threads about 4-stroking

unless motor is reving really high while bike is going slow, it isn't the clutch
 

javy mcdees

Active Member
Jul 30, 2018
143
58
28
49
just started the MB deal few months ago and started out with my old bad habit of mixing super rich mix of 1.5 ounce of 2 stroke oil to a gallon of gas and tuned off that and so far runs awesome everyday just put 35 miles on her today. running a 39 rear tooth and runs 30 mph cruise and will run right up to 40 mph ready to rip the wrist pin out the piston or blow a hole through the middle of the piston. The NT carb ran good until I took a hammer to it. now use the Runtong carb runs better, better mpg and more top end, even the low end is acceptable. Just had to buy 3 of them to get one that worked.Make sure the cap is tight on the NT carb that holds the slide in, if it is loose it will pull in air and run like the OP issue.
 

Attachments

Tyler6357

Well-Known Member
Mar 15, 2012
1,142
170
63
Santa Barbara, CA
1.5 oz of oil for each gallon?? That's 85 x 1!! You better thickin up your mix or your engine will burn out, unless you are using Opti-2 you should be mixing 4 oz of oil for each gallon for 32 x 1.
 
  • Like
Reactions: Venice Motor Bikes

javy mcdees

Active Member
Jul 30, 2018
143
58
28
49
1.5 oz of oil for each gallon?? That's 85 x 1!! You better thickin up your mix or your engine will burn out, unless you are using Opti-2 you should be mixing 4 oz of oil for each gallon for 32 x 1.
Ok let you know when I hurt an engine, still going good so far like always. Today ran out of 100:1 now running 50:1 Dominator so far no smoke and no issues.