GK76 Big starting issue

[FH700]

Hi all,
Had I only discovered this source of knowledge (gathering of more 400 freaks) earlier...
I've been hassling with my GK76 for weeks now, and she drives me crazy (and not with suberb driving and steering like she used to do).
What does and doesn't she do:
Starting is the big issue. Sometimes there is a spark, but it isn't always a strong spark and it isn't consistent. But actually most of the time there is no spark at all.
I managed to get her running again (with empty carbs and starter-pilot, to be sure that she didn't get to much fuel) and she ran perfect. But the next day she started running bad again. After that she didn't start at all, no spark, again.
(The empty carbs + starter-pilot didn't work again)

Checked:
- resistance on coils (with and without cables+caps) > ok
- resistance on pick-up coil (on the connector at the CDI, so that rules out the connector inbetween) > ok
- ground on CDI > ok
- input CDI is exact like the Ubat > ok
- the power supple on both coils is exact like Ubat > ok
- spark plugs were changed allready a few weeks ago > ok (are could they be bad again allready?)

- I've tested the steering signal from CDI towards the coils with a scope a while ago, and at that moment (cant check it now anymore, because I had to bring the scope back to its owner) the signal looked ok, the 1-4 coil and 2-3 coil were ok, the timing seemed to be correct in order to the TDC and the pick-up coil refered to the TDC correct aswell.

Does anybody recognise this behaviour and/or has some good checks for me that could lead to ending this torture?

Thanks in advance!!!

/ Edit, my apologies for this sudden question. Maybe a little rude from me to not intruduce myself first. My drive for solving this problem at a short notice, won from the manners my parents tought me.

[morris147]

Coils should be 1-3 2-4 If i remember correctly...

[Variablevalves suck]

Coils are 1-4. 2-3. If the o'rings are bad this could give bad starting, CR9 spark plugs give bad starting, but if you are getting a weak (yellow) or intermitant spark i would be looking at the electrics first.
Bad battery, electrical connection. BUT worth a look is the pick up at the point the wires leave the engine cover, ive had bikes run and then stop with correct pick up measurement due to the wire braking at the bend and then the spark is yellow.

[stripes1976]

Coils are 1-4. 2-3. If the o'rings are bad this could give bad starting, CR9 spark plugs give bad starting, but if you are getting a weak (yellow) or intermitant spark i would be looking at the electrics first.
Bad battery, electrical connection. BUT worth a look is the pick up at the point the wires leave the engine cover, ive had bikes run and then stop with correct pick up measurement due to the wire braking at the bend and then the spark is yellow.

But also check the wiring around the fuse box.
Battery
Crimped joint in the pick up wiring.
But i also would check compression.
Air leaks around intake.
And o-rings on vacuum ports.

[FH700]

Thanks for the comments!

Bad battery
> I checked and measured all with an extra (car)battery connected with jumper cables

the pick up at the point the wires leave the engine cover
> I replaced the pickup with another aswell, same measuring and didn't solve the problem. Also visual the wiring looks ok there.

But also check the wiring around the fuse box
> I've got 12V at the CDI aswell as at the coils, also when I push the starter button the voltage doesn't drop (that is: it drops to the same voltage as the battery itself)

But i also would check compression.
Air leaks around intake.
And o-rings on vacuum ports.
> Could cause starting problems, but then still I should get a good spark.


Any more comments to this? Or am I forgetting something stupid?
The one thing I didn't do is replace the CDI, but that is because I can't find any in Holland.

[stripes1976]

i've had a few where the contacts on the kill switch have been corroded. strip the switch and clean the contacts.
Have you tried borrowing a cdi a seeing if it makes a difference?

[dobbslc]

Check the wiring under the left side seat panel. There is a small diode hidden in there that corrodes.
Clean every plug you can find with proper contact cleaner & check all of the earthing points around the bike.
As Stripes said clean the kill switch too. I also found one bad coil that caused all kinds of starting & running problems (stalling when the lights or cooling fans switched on etc)
I did this all with mine and it now sparks well...

[bayz]

Have you tried borrowing a cdi a seeing if it makes a difference?

I dont know if you have solved this issue yet..

I had more or less the same problem with my current GK76 project .. and it was caused by my cdi..
As i said in my other post, my cdi was totaly messed,.. instead of sparking 1-3, and then 2-4.. it was sparking al four at once 1 and 3 would have strong spark.. then 2 and 4 would have a weaker spark.. but besides for that, it did the same as yours,.. then it would have spark.. and all of a sudden the spark would be gone again ..

so naturally i started looking for the problem at the end of the problem line,.. changed plugs.. did the same,.. made sure that the suppressor caps was properly screwed on and not loose.., that was fine, so moved a step back.. checked the coils out, wasnt sure what i was expecting to find there so i moved on.. i checked all the wires going from the coils and traced them to make sure none was broken or cut open to cause a short circuit that throws sparks away.. that was fine as well.. then onto the CDI.. thats when i realized my spark order is entirely wrong.. but it still didnt explain why i have spark now,.. and the next moment have no spark.. so i left it there.. thought to myself.. well the CDI is messed up, so let me get a new one first to solve my miss fire, then when thats fixed ill sort out why i loose spark..

and to say the least, when i changed the CDI not only was my firing order fixed, but also i didnt have spark loss anymore ..

so i go with what stripes said.. borrow a CDI that you know is not faulty from a friend and see what it does..

[ben2306]

sorry guys, like to ask.
how to you know which plug got spark or loss of spark?
if sitting on the bike, which plug should be 1,2,3&4? cos recently, i just changed the coils, scare the mech anyhow plug. i know there's 2 coils, so the left 1 should be with which plug? & how do you actually know which plug sparks 1st? lolx... so sorry. still learning...

[jamierooney]

To the OP, I have to say - you have gone through EVERYTHING that I did, and the only thing that resolved my problems was to clean the engine mounts as they were preventing the spark plug from completing their circuits to earth. EVERY SINGLE other option had been checked prior to this, and an easy test (before removing and cleaning the mounts) was a mighty big jump lead from the engine (anywhere there's some bare metal exposed) to the earth on the battery. As soon as we did this, she fire first time EVERY time.

Try it - it should only be a 2 minute test - and you should know then.

Rgds,
J