Author Topic: Thoughts on 125 twostroke powerband?  (Read 746 times)

0 Members and 1 Guest are viewing this topic.

Offline John Orchard

  • Legend
  • *****
  • Posts: 3041
  • ^^^ July 1984
    • View Profile
Thoughts on 125 twostroke powerband?
« on: January 19, 2023, 07:04:49 PM »
I've got a bit of a mental-block, so,'77 TS125 suzuki, ported to RM100 (50mm stroke) specs, RM100 pipe, VM32, the bike has an awesome midrange, revs out nicely but no top-end power.

I'm running stock ign timing with a high compression head, maybe I need to retard the ign timing? I'll have a bit of a play with jetting, might need a bit more fuel, ideas welcome, thanks :-)
« Last Edit: January 25, 2023, 02:04:37 PM by John Orchard »
Johnny O - Tahition_Red factory rider.

Offline sleepy

  • Legend
  • *****
  • Posts: 803
    • View Profile
Re: Thoughts on 125 twostroke powerband?
« Reply #1 on: January 19, 2023, 08:14:03 PM »
How old is the pipe, maybe full of carbon. Timing could be an issue as well as jetting.

Offline John Orchard

  • Legend
  • *****
  • Posts: 3041
  • ^^^ July 1984
    • View Profile
Re: Thoughts on 125 twostroke powerband?
« Reply #2 on: January 19, 2023, 08:27:12 PM »
How old is the pipe, maybe full of carbon. Timing could be an issue as well as jetting.


Thanks, no carbon build-up, maybe the comp is too high? Wouldn't have thought it'd rev out so freely if too much comp? Confirm jetting first, then try timing. Failing that, an extra head gasket. thanks :-)
Johnny O - Tahition_Red factory rider.

Offline sleepy

  • Legend
  • *****
  • Posts: 803
    • View Profile
Re: Thoughts on 125 twostroke powerband?
« Reply #3 on: January 20, 2023, 10:15:50 AM »
Unless your CR is stupid high I doubt that would be the problem. Years ago I did a Yamaha Gokart engine for a chat that wasn't racing just weekend playing. He wanted the motor made bigger and I managed to stretch it from 80 to 110 cc and on the first outing with indentical port timing to stock it had heaps of midrange enabling him to pass his mates out of the corners but wouldn't rev so they would pass him 3/4 down the straight. I adjusted the port timing and fixed the top without loosing mid. 

Offline John Orchard

  • Legend
  • *****
  • Posts: 3041
  • ^^^ July 1984
    • View Profile
Re: Thoughts on 125 twostroke powerband?
« Reply #4 on: January 24, 2023, 09:29:04 PM »
Fixed it, I'd fitted a piston with only 2mm off the skirt, thought it was more, just fitted a piston (RM125S) with a 6mm shorter skirt, that found the top-end :-D
« Last Edit: January 24, 2023, 10:32:40 PM by John Orchard »
Johnny O - Tahition_Red factory rider.