kh125, I need help!

[Graeme77]

I have a kh125, have had it for ages. Its never run. Previous owner couldnt get it running. Owner before that rebuilt it.
I tried everything, then laid it up for a year.
I just stripped engine, rebuilt it and am trying again but it still wont run!
 Carb is spotless.
Rebored, new piston, rings, bearings and seals.
Got good spark (but no battery power, shouldnt matter).
Cant see any way to adjust timing except by altering points gap.
Ive had the rotary disc valve in both ways round.
Got cood compression and clean posh petrol. Petrol is getting to carb, plug is getting wet but might just be oil. Ive tried a bit of fuel down the plug hole and ive tried brake cleaner squirted in the carb lol.

I just dont understand why it wont run!

Anyone know anything about kh/ke 100/125?

Im at the stage now where I just want to set fire to it.

[matthewmosse]

I have one, was my first bike, love it when it works, hate it when it breaks which seems all too frequent. Timing marks on mine were out so I had to set and adjust using dti gauge ( I made up a dummy spark plug to hold the dti gauge to determine true topmdead centre)  and extra base gasketts after it developed a habbit of blowing holes in pistons. Even experienced pro rebuilds have failed to get true reliability, but boy the bike is fun when working. On mine I had lots of issues with spark plugs that wouldn't run it, like they were fouled but they were actually clean and sparked outside the cylinder but once installed, no go. New plug would sort it but had about 3 started missbehaving after  few minutes. Eventually cleaning with a brass brush and carb cleaner might render the 'faulty' plug working again. I have about 3 bikes of this ilk in an attempt to get a decent engine but so far not got there. I intend to go though the lot at some point as given a decent clear run at it I reacon I should be able to get 3 engines built up and build the bikes up to runners in a week. Famous last words, I bet I get 99% of the way there and have 3 bikes cluttering up the shed that all refuse to run. I think the ngk iradium range plugs proved a bit better, and I may have replaced the coil in my quest to get her running when I had a spark with plug out but no running when plug in.

[Graeme77]

Thanks.
so new plug next and maybe a good known coil.
In your experience, will they start ok with a completely flat battery? Its 6v so I cant charge it yet.
Usual story, dont want to spend money on it till it runs but needs money to get it running.

[matthewmosse]

I seem to remember mine was ok to run sans decent battery, but I think I had the old dead one still connected, and whilst it still had some tiny trace of life it ran, I vaugely recall that it eventually demanded a new battery to even start when the old one gave out and no longer gave electrical continuity. The saving grace of these bikes is batteries and virtually everything else are so cheap. I think a coil was under a tenner and the same for a battery when I last looked at mine, which was a few years ago.

[Graeme77]

Thanks. It has a battery but its been flat for years. Ill get another.

[AshimotoK0]

Thanks. It has a battery but its been flat for years. Ill get another.

When I was a poor student back in the dark ages, I used a large electrolytic capacitor on my CB250K in place of a battery. You would just need to check that the 125 has some sort of voltage regulator.

http://www.ebay.co.uk/itm/Capacitor-10000-uF-40VDC-Electrolytic-Radio-Spares-/311444547316?hash=item48838aa6f4:g:nRcAAMXQRPRTIeYn

[matthewmosse]

It is 6v and has a 3 wire regulator behind the tank and a magneto ignition. I think the regulator did not like running sans battery as I had to replace it around then. Only just remembered that when you mantioned it.

[Graeme77]

Fitted a new plug, charged battery, bought easy start, still wont run.
its got spark, but dont know if its sparking under compression. I only have the front exhaust pipe fitted at the moment and its dripping with a fuel/oil/easy start mess so fluid is obviously making its way through the engine.
It must have no spark.
Any things to test? Ive been trying to measure voltage at the coil when its kicked over but its inconsistant (and low) but im clutching at straws. Dont really want to replace battery, coil, regulator, stator and rotor without knowing whats at fault.
Bike needs work, its rough as its been sat in the garden. I dont mind spending on it if it runs but dont want to throw £200 at it in the hope of it then working.

[Graeme77]

The offending pile of junk.

[Graeme77]

And a pic of my cb750 to brighten things up a bit

[Graeme77]

Took the top end off again and have been poking the multimeter about.
Coil has 5k resistance on the secondary but only 0.3 ohm of primary. I guess its knackered. Ill order a new one and see if thats it.

Im still not convinced its drawing fuel through properly but I cant see why it wouldnt.

Its maddening, multi cylinder 4 stoke I can fix, 2 stroke with 3 moving parts and im stumped.

[matthewmosse]

They can be very finincky. Mine was a first kick starter for a couple of years, then some W**sok who was meant to be a mate decided it would be funny if I thought it had been nicked, only thanks to the lock they just managed to drop it, breaking the mirror off and disconnecting the 2 stroke oil bottle, the mirror was stuffed back into the hole badly and the pipe disconnection was inside a cover so the first I knew of this glorious prank was the mirror fell off nearly hitting a following car, not long after the engine locked up. Then Bt rang to say I had exceeded the £100 credit limmit on my new landline - having made about 2 local rate calls to my parents, same mate had run that up in a fortnight calling god knows what premium rate numbers on my phone. Friends eh? Compared to that a few engine siezures from the bike made it the better company. The bike has stayed with me. The friend is long gone. My kh would deffinately grace a skip if it were not my first ever bike. I have the factory manual for it if you need any info from it.

[Graeme77]

It would be very helpfull to know the coil resistances and exciter coil resistance.
Would also be good to see a picture of the disc valve as fitted, or any info that would give me a deffinate answer as to which way round the disc valve is fitted.

The plan with this bike is a run around for the wife, but a little tuned, stripped down, expansion chamber and a 60's style race fairing to mimic the old A1R racer.

[NigelWilmshurst]

Welcome Graeme
I grew up on tuned up 2 stroke twins, still love to hate them, they become part of your soul!
Spark plugs not working under compression were always an issue, as Mathew says iridium spark plugs or similar are a good investment, back in the day we had NGK R plugs, if the new coil doesn't solve the problem I suggest meticulous points and timing set up is essential, I used to have to reface the points with a chisel sharpening stone every 50 miles or so to maintain the power band,
Buy new points and condenser or strip the points into 2 parts and re face perfectly level, check the timing is exact, all else fails clean the plug and use a lead pencil to draw over the electrode and heat up with a lighter, then put a cap full of petrol down the plughole, put the plug back in and fire it up!

[matthewmosse]

I belive the tuning mod for these bikes is to bung a larger bore carb on. Numbers are someting I cannot recall at the moment, but I think it sports a 19mm mikuni, and a 22mm one will unlesh a few extra horses, at one point I discovered mine had had this little mod, about which I was not ammused as I was on L plates back then, plus I rather suspected it might have contributed to some of my troubles with reliability. I hope to dig the manual out later for you.