kh125, I need help!

[matthewmosse]

Ok, found I have 3 copies of factory manual as you look at the disk valve installed, if the carb inlet is at 1 o clock then on the crank there is one cutout that is wider on the centre of the rotary valve, as the rotary valve just clears the carb inlet going clockwise  that wider cutout in the centre should be at about 4.30.
Apparently it is marked by what looks in the photo like a scribed line, possibly with a direction arrow. It doesn't show up on my camera very well at all.
ignition coil resistance - primary winding meter @1ohm reading should be 0.4 -1.2 ohm secondary winding meter @ 1k ohm reading should be 4- 8 k ohm
magneto resistance meter @ 1 ohm, reading should be 1 - 3.5 ohm
hope this helps. I am happy to scour for further info if needed.
The manual does stress the iggition coil tested by these readings is not definitively tested and reccomend the use of a kawasaki electro tester that makes the spark jump across a 5mm gap as this tests for layer shorts or insulation breakdown under high voltage. In all probability an electro tester is more cost than a new coil....

[Graeme77]

Thanks, very helpfull. Seems my coil is only just about out of spec. I was hoping it would be way off spec and therefore more likely to be the problem.

As for the disc, im struggling to visualise your explanation. Ignoring where abouts in the rotation it is, the larger center notch, is it nearer the opening to the right, or nearer to the left?

Thanks again, much appreciated. Im surprised how little info there is on the net about these, they made them for long enough!

[matthewmosse]

On the right. I may try to get that page scanned tomorrow and post as a picture on here. Rotary disk has a service limmit thickness of 0.52mm and normal thickness of 0.67 to 0.73mm, the cover for it should be 1.1 -1.2mm deep with a service limmit of 1.5mm.

[matthewmosse]

Better lighting helps, energy saving bulbs....

[Graeme77]

Fantastic, at last I have a definitive answer to which way it goes in and luckily, thats the way I fitted it.
I hadnt even considered it would wear or any of it would have a service limit! Im not taking the clutch out again to check lol.

So mechanicaly the engine is fine and electrically I cant find any issue so im left with randomly replacing parts till it runs

[Graeme77]

Yes, 22mm carb peps them up. Also 4mm of the disc valve each side. Those, the expansion chamber and maybe a bit more compression is all id do.
I have found a 12v comversion with rotor, stator, regulator, coil erc for £200. Pretty much replaces everything and gives electronic ignition and 100w of generator output.

Im tempted.

Ill try a new coil and if it runs ill think about investing. Reliability is good when its my wifes bike and it will be me getting the call every time she cant start it!

[matthewmosse]

Iradium plug, then new coil, probably a battery, you should get change from £30. If you are lucky, then you'll have a dead 12v battery awaiting scrapping that gives off 6v to get it up and running.... as long as you don't want to go far or bungee the battery to the seat. Glad  I dug the manual out as I can now remind myself of a few details, might even inspire me to sneak the kh engines into my loft in the house and do a sneaky rebuild in the warm, dry and electrcally lighted space rather than in a windowless draughty shed whilst stood in a puddle. That loft is looking tempting after a bit of a tidy up when fetchinb the tree and decs out.
12v conversion, do tell me more!

[Graeme77]

https://www.powerdynamo.eu/shop/show_product.php?cPath=4_46&products_id=570&SESS=4ru07autj8foqt8vjnf82585rusb0539nghuj4emd3br98klne71


looks good doesnt it!
Would solve alot of problems.
Thing is, if I get it and it still doesnt run id be really stuck!
Ive had the engine apart and everything looks new but I still dont quite trust that its drawing properly.

[matthewmosse]

I shall cirtainly be thinking of that carefully, not for a while though, got my new car and the family run about to mot this week, first time in my life that I am ducking out of bikes for the colder bit of winter, new job, 6 am starts and a modern bike that is rotten on ice. I wonder if the cost of 2 cars will finally give us the push for me to fix the cb500/4 sidecar, though I was kind of hoping to semi retire it and not trash it further on salted roads every working day.

[Graeme77]

I gave up riding in winter the second year I was riding!

Been having another go at it, checked everything, re annealed head gasket too. I opened up plug gap to 'huge' and spark jumps no problem. I set timing perfectly with my meter.

It should run!
Doesnt though.

Wondering if I have compression issues. When doing the timing I can turn engine over easily by hand with the rotor. Not much resistance at tdc. Its got a fresh (perfect) bore, new piston and rings and all surfaces and gaskets are good though so no idea why it could be low. Do 2 strokes have proper compression when being turned over slowly?

You can see someone has cleaned up the exhaust port a little on the sides but the opening hasnt changed so I dont thing thebports have been messed with.

loads of compression feel when using kick starter though.

[matthewmosse]

Crank seals and the rotor disk are part of the seal system in these I think, they do turn over easy though.
I believe my mate who knows them moderatly well says the crank seals can perish or go hard and loose you compression if I recall correctly. I just dumped 3 dismantled engines in his shop and collected 1 decent one and left most of the details to him. Like I say, plugs sparking fine outside the cylinder but not running was an infuriating problem, and I ended up with about 10 plugs that sparked fine but would not run, normally after a few minutes use. Not a clue why, all ngk plugs, but from different sources and a decade appart in age.

[Graeme77]

I stripped the engine this time round as I suspected crank seals but they were new, along with new crank bearings and big end and small end. That was only 3 years ago but it hasnt run since. Has been full of oil though.they all seemed supple and spot on.

Im going to a local 2 stroke place and bike breakers tomorrow to pick up a coil. Ill pick their brains and see what else they have.

I think its getting close to crunch time, either just spend whatever it takes even if thats a few hundred quid and comit to getting it sorted or give up and find her a bsa bantam.

[Rozabikes Tim]

Graham,

Who are the 2 stroke specialists and where - Chesterfield? Just a friend in Wirksworth has just bought a 250 yam ? Not running cleanly and he was after said expert....

[matthewmosse]

You will pay a premium for a bantam and I would bet the kh would blow it away in economy and preformance, spend on the kh. At a geuss a bantam will be a worn out wreck that needs a lot of new bits to get right. They are all getting a bit old and have probably done a lifetimes work already. I know where I would spend my money, my last rebuild was £127.88 inc parts ( main bearings and seals etc) and labour, though the spitefull kickstart shaft snapped a month later. Whatever else you can say about the kh, it is very cheap on parts.

[Graeme77]

Yes, bantams will be knackered, expensive and slow. But, I like em amd the wife loves them. I also recently discovered they still race them and a 125 bantam can be tuned to top 100mph
I figued a stupidly highly tuned and unreliable 80mph rigid framed D1 sounds like fun.

As for the specialist, I may be over hyping them a bit. Im talking about syd smith in sheffield. I say 2 stroke specialist as they deal alot in motocross parts where as all the other places I know only really deal with 4 stroke stuff.