Hey guyz,
Not vw but aircooled none the less :-). Having some troubles with my 125 4 stroke trail bike.
After doing some work to my engine and putting it back together its not quite running right, it seems to have intermittant power...?
Its just rideable, but when riding it is lacking alot of power. Intermitantly how ever it will running 'right' and be powerful and run well, but only for a short period of time. For instant had it pinned in 2nd and was just thinking, what can be wrong. All of a sudden it started running 'right' and lifted the front wheel, i kicked it into 3rd and it just died again.
Its still got small flames coming out the exhaust if i work the throttle for it, which leads me to think the charge is not combusting properly, leaving the head then the next cycle and charge will ignite, which then ignited the unignited charge from the previous cycle that has now entered the exhaust pipe.
I have cleaned the carby.
Cam timing IS spot on.
Do have spark, but i cant tell if its intermittant.
Im pretty sure valve clearances are right.
Have tried a spare CDI, no change.
This list leaves me mainly focusing on the ignition system, possible a problem with the magneto, coil, or wiring. Yet intermittant power does not seem to be the result of a loose or bare wire as it is not bump related etc.
I have got a spare coil, i will try that next.
This has got me puzzled, any assistance, ideas, possibilities or experiences would be very useful!
I would have said coil/magneto. Maybe bad plug lead contacts? Sounds like a resistance change in the ignition circuit maybe, that wouldn't be affected by bumps.
A POSSE AD ESSE.
I live in my own little world, but it's okay, they know me here.
did some head work, porting, shaping, etc. Havent touched float level or air bleed, it was running fine before the work so i wasnt focusing on carby, but now its running rich i think it may b more likely.
Put a new plug in and it ran better, but really rich, and the plug is now fouled.
Am borrowing a spare carby off a mate to see if thats where my prob is.
Hopefully that is the problem... $20 fix off ebay :-)
heres a vid of it running.
i think the sound and image are out of sync which is annoying coz u cant see throttle position. But the sound is delayed by a sec or so, you will pick it up after you watch it.
ill post again this arv and you all know how the spare carby went, fingers crossed!!
I did notice it was firing out the carby tho, which suggests a timing issue either spark (wasnt very powerful blow out so i guess this) or valve timing, which i have spot on unless the flywheel is one rotation out, but it shouldnt matter... should it?
I guess what ive got left to try is take the timing gear off, spin the flywheel one rotation and bolt it all back together.
I can hear a bit of a ticking noise, sounds to me like valve lash... so hopefully nothing serious.
So now i have rulled out:
Coil
Spark plug
Ignition lead
carburettor
compression (sort of.. need a helper to get accurate reading)
All thats left:
Try valve timing with flywheel rotated 1 revolution
Ignition timing (same as above i guess), Have to do a bit more research on this.
Valve seating/seal
any ideas? Am i heading the in the right direction?
UPDATE:
Just spent 30 mins ruling out valve timing.
Must have damaged the magneto or something like that. Ive got a spare so ill whip it off tomoro and see how its goes.
so much for chinese simplicity lol.
Few more things to cross off the list,
Valve gap, both have clearance over the TDC period and both valves open and close as they shud (no sticking etc)
valve timing, spot on, tried it in 3 diff positions, no change at all to the running...
This f* up has gotten personal now lol, my sanity is at stake.
either i get it running soon, or its going off a headland in flames! (d/w will have vid cam if its the latter)
