Two Stroke Help!

[rickam03]

First post here so ill try not to be too vague!

My first bike i have bought is an old '86 NS125f, i love it, but unfortunately the feeling is not mutual. Was insured less than a week before i could not ride it, as i was heading down the A2 and lost all power, since then i have not been able to start it up again (2 weeks ago) i have since replaced the piston and piston rings, the cylinder was absolutely fine considering the age. New spark plug and a general top end rebuild. Spark is fine and gap is fine.

So i did a complete oil change and also changed the clutch springs while i was there (still awaiting clutch plates as the clutch lever is excessively hard to pull) built her back up and now the kickstart is much harder to kick and she still doesnt turn over! tried bump starting etc.. Im lost.. had a friend over who granted isnt a two stroke expert, knows his shit and he is baffled. He expects it to be a fueling issue, but the engine will backfire down the exhaust at irregular intervals.

I have spent too much money on this bike already (lol) and i really want to know what it is best doing as im not willing to be charged out the arse for garage work just yet..

If anyone can help me that would be very very very very very much appreciated.

[Vincent]

Backfiring suggests ignition........'might be worth checking all the ignition contacts - on the coil, CDI, pulse pick-up etc. Check the plug on the reg/rec for overheating too and see if it's working by checking battery voltages, (not sure if a duff reg/rec will stop an NS125 from running).

Have you got a manual?
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[bikenut]

flywheel key sheared??????

you say the engine will not turn over?? ie the piston does niot go up and down and the flywheel /crank does not rotate??
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nuts about bikes

[MarJay]

You haven't been very clear. Do you really mean that it won't turn over? Or do you mean that it turns over and won't fire?
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[Taught2BCauti...]

If you've had they flywheel off, check the woodruff key was in place when you put it back on!

Sometimes, the woodruff key can fall out whilst the flywheel is off - and if you weren't aware, the ignition timing will be off.
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[rickam03]

Sorry for the vagueness,

the engine doesnt start up upon kickstart, pistons will move up and down and ive had the spark out and there is deffinitely compression in the cylinder, have even tried putting a small amount of petrol into the cylinder, and it just backfired out of the exhaust.

[rickam03]

if it helps, up until the engine died on me on the road, it worked a charm, revved high and accelerated well, never realised any issue with the bike, upon rebuilding the engine the old piston was fucked and rings shot, the lass in the car behind me was a friend and saw a spark come from the exhaust as this happened (before the back wheel locked up and i started sliding)

i do not have a manual no.

[Vincent]

I presume the back wheel locked up before you rebuilt the top end...ja?
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[rickam03]

yes, the back wheel locking up and the loss of power which lead to a dead bike prompted me to rebuild the top end.

[bypass2]

as said maybe the woodruff key. how old is the spark plug try a new spark plug. is there a good flow of petrol from the petrol tap to the carb have you had the carb off and restricted the petrol flow.what about the HT lead/plug cap faulty

[rickam03]

New spark plug was put in and the spark is fine, did the old put it against metal trick. Most likely be this key? Although I did out of stupidity kick the bike over while it was in gear and it did jolt forward.

[Pete.]

Where in Kent are you?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[andys675]

aren't the pistons in these marked A/B/C to get the clearance right?

have you checked this?
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[Teflon-Mike]

It's a 28 year old 2-smoke. Likely thrashed whenever ridde by succession of kiddie-go-kwik owners, with minimal maintenence when-ever it's broken so bad as to not move.
I would suspect its probably never had a full engine rebuid, and at 28 years old, eve if nothing more is buggered down below, I would imagine that the crank-case seals have almost certainly seen better days, and are likely to be hard and not best sealing... if not, then you can have all the compression up top you want, but no good if you have no compression down below to shove it up top.
However, as mentioned, check rotor wood-ruff as first port of call... actually no... check the fucking manual as port of call! What the hell you doing trying to rebuild an engine without the book! Where did yo get things like cylinder head stud torque settings from?
THEN check rotor key, then check your exhaust for pin-holes. 2T's are exhaust sensitive, harmonic resonance is only reason they work... any hole or leak in the pipe screws that up and they dont work. Most 'carburation issues' tend not to be in the carb but in the pipe... Also.. did I mention GET THE FUCKING BOOK! Answers so many stupid questions so you don't have to ask them here And tends to be more useful way to spend £20 than on a back-street mechanic to 'have a look' and tell you its not worth his time to fix it.
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