Hi guys I have a engine here from a 1974 125a roller.

No case markings so it must have replacement cases.
And is running a 40100 cylinder which is mx125a and then has 402 on the flywheel so is a mx125a engine 

I want to find the timing specs and double check thats right too.

Also had no carb and am trying to use a keihin pwk28 from a cr85 which runs a 35 idle and 128 main.
 Bike starts first kick but won't rev past quarter throttle .
I have tried a 110 to a 150 main with no difference.. 
Happy to buy a new Mikuni vm if needed as jetting will be listest in a manual 

  

Ok, my first & only guess at the moment--is--the second stage of the pulser coil is out of order. With 'that' type of pulser [trigger] it starts on the retard part then flicks magically to advance. Colors will be green/white & red/white [& guessing black], i'll go look later--plugs will be two separate double plugs more likely than a single 4 plug. As usual i might be wrong but [if it was that] it wouldn't get above an idle on full throttle.

found my book for an MX360 using the same style inner rotor cdi mag. Says white/red to white/green=50 ohms. then gives White/Red to Black= zero reading. Not sure that's right for last reading. i'll delve deeper. But on second thoughts it will be right as black from the cdi box goes to earth on stator black. & if any reading from the pulser trigger colored wires would mean an internal short in the pulser.
Also, charge coil Brown to Black=790. Then Red to Black=84.

Ok, hold that thought, might be wrong. Do you have a white/green & white/red coming from the pulse. If only a white/red then it'll be a single stage pulser [that i didn't know these had] But i guess 125's don't need retard to start as don't kickback hard like a 360. Just trolling manuals although no 125 manuals & getting confused as no two manuals for the bigger motors read the same.

I give up--or half give up. Here's a drawing pic of a YZ125A 1974 & can see the pulser should be a two wire because of two magnet strips show on the rotor=start then advance. Let's now what yours has. 

Ok, sorry i'm hogging your post, but just found a genuine yamaha service data sheet covering 1975 YZ125C which is the last year of the old style stator & reading are--Br-Bl 790. R-BL 80. W/R--W/G 50. W/R-Bl=00. I'm preparing to look stupid if its only a carb problem lol.

Will check this tonight mate and let you know 

Is thios you on another forum i stumbled on by by chance haha. Can see the two wires green/white & red/white in this pic. Cheers.ps, Check how good the connectors fit as they plug to the box. Just rethinking everything i've said previously i wonder if it has a source coil fault as think they have two & could be that the main one is ok but topuip coil is faulty & can't crank the voltage to go to advance & rev out. God i hate electrics when i'm guessing alot.
Here's a different take on it that i've told before--but!!. My DT360A with full flywheel but same type trigger--just magnets around outside rather than underside--Wouldn't start [no spark] but was a faulty first half of the trigger], so wired it to the advanced half & never looked back except had to kick it hard to avoid kickback. Yourse is sort of the exact opposite problem. If trigger check out with continuity then check connectors but defo check the two soucy coil things red & brown. I'm now guessing the Red to Black will test open.

Nail on the head mate
It was one of the 3 plug wires you suggested. I'm guessing it was one of the timing  advancing circuits.
thanks mate!

Cool, that's good. Had me worried i was loosing my touch haha.