125 SM revving problem

[Jamie]

hi guys,

Could do with some help on this one.
Just stripped and replaced the piston in my sm125, rebuilt it got it running and the bike wont rev, i open the throttle and it just revs at constant speed no pick of which to speak.
I am wondering if its the ring aligment, loose rubber, or plug.
No oil leaks, no smoke from the exhaust, no water in the oil or vice versa.
This one is beating me, then i thought of all the knowledge on here.

Any help would be appreciated.

Jamie

[DAVID THOMPSON]

check the intake rubber holding the carb on the head
and did the cable come unhooked from the slide in the carb while it was apart
Dave

also if new parts piston and rings dont expect it to rev high till its got some miles on it

[Jamie]

I will recheck all of them.
No the cable did not get disconnected, but worth a look.
Do i have to reset the valve clearances for replacement piston?

Will get back to you either way.
Thanks Dave, I knew i could rely on you or someone on here.

Jamie

[DAVID THOMPSON]

also check to make sure choke is not still on or stuck open (fuel enrichment valve)on carb

if the head is off the bike then the valves need checked
but may be OK
Dave
never done it on the 125 yet and not looking forward to it
as it will probably cost toooo many $$$$$as it requires parts to do

[Jamie]

Well dave, did as you suggeted, wasnt the choke or the carb slide.
The symptoms are, full throttle only produces what seems to be half throttle revs, for a while, then some smoke and cuts out, it seems to be that there is not enough fuel being drawn into the cylinder, and then it runs out of breath, which seems to be a ring problem, so stripped it, to find a lot of carbon on the valves, which wasnt there when i did the first striop down and the oil scraper ring was not too good.It broke whilst trying to re assemble
Will need a new one, not to bad £25 from Grahams.
My question is do i need to recheck the valve settings? on re assembly, and how do i do it.

Jamie

[DAVID THOMPSON]

not sure about the valves as i have never had a bike with the shims before
dave

[Jamie]

UPDATE, well Dave got it all back together and working,
its been running a week now and better than ever, just needed the rings to bed in.

Thanks for your assistance.

Jamie

[DAVID THOMPSON]

when mine was new it took about 3000 miles before it seemed like it was broke in
now at 20,000 miles it seems like its getting a bit tired
but still runs good for what i use it for running around town where the speed limit
is 45 mph or less
Dave