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'79 GS850g cam chain stretched or what?

  • Thread starter Thread starter svahnm
  • Start date Start date
S

svahnm

Guest
Hello folks,

I have some performance problem with my engine. It works fine idle and quite fine with half throttle untill 4000rpm, and after that starts to pop and cough specially if throttle is opened even more.

I wonder if my cam chain is still in good (or adequate) condition? Before the main question I give a brief what happened and what I have done already. If my brief is too boring to read jump to question chapter...

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Everything started while cruising normally at 3-5k rpm. After next turn on the road I applied more throttle and realized that power is missing. Sounded like 1 or 2 cylinders missing. I pulled over and checked spark plug wires and caps (new coils, wires, plugs, electronic ignition). All connected well. I headed home (10km) slowly 2-3k rpm gentle throttle. At home I checked ignition timing (freshly installed Boyer transistorized ignition, new coils etc...) and realized that ignition timing plate had moved little bit (looked like). I have had troubles to keep it steady, because it is made of circuit board material and I was afraid to tighten it too much.. It has slided before also. I timed it first without lamp roughly, but top power was still missing.

I started to suspect that cam chain would have jumped or something.

I checked timing and Clymer manual says that when crankshaft is TDC, then exhaust cam sprocket's arrow no1 should point forward head level or preferably 1-2mm below. Then intake cam (can't remember those numbers in sprockets now..) should point to 20th chain pin counting from exaust cam's another arrow.

What ever, after noticing that when sprocket arrow was pointing head surface level, crankshaft was pointing out of TDC maybe 5-10 degrees. Looked like 1 teeth had jumped?? I had to take cams out to be able to jump the chain easier. I pulled away slack from chain and installed it on exhaust cam sprocket. Counted 20 pins to intake sprocket's arrow. Installed that guide thing and tensioner by the book (At least as I understood).
**********************************************
Conclution is that I can't make that exhaust cam sprocket's arrow pointing exactly aligned with cylinderhead gasket surface or little below when engine at TDC. It is pointing few mm above the surface or almost 5mm below (depends which teeth I use of exhaust sprocket).

Furthermore, camshafts are not pointing exactly towards (when aiming those grooves right end of camshafts). Exhaust cam is more advanced (like chain would be stretched). Is this normal?

Is it really so rough timing?
At the moment I don't have time to repair it more :cry: (or my wife strangles me if I don't finally finish our building project too) but winter time I am going to fix it and any help is needed specially now when I still remember what I did with camshafts...

EDIT: And yes, I don't ride with that a single meter before I fix it...

I apologize too long post...:oops:
 
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The timiing was probably fine before you messed with it, With factory marks they are close not exact... I would check the gas for water, crap. Then I would check the coils/wires/caps & your Boyer ign. CHeck the valve adjustment.
 
Thanks, valve clearances I checked after installing back camshafts-> ok.

I think I will move chain back to its place and start with fuel and spark anyway.

Is there any chance that only carburetors would cause that loss of power on high rpms and open throttle? Just asking because I just "fixed" ignition with new parts, and if it would have failed again, I am at starting point again.:(

Oh, I tried also with petcock PRI position, but I should check fuel flow overall..
 
I finally found the reason for rough and powerless operation -> ignition, again...

Thanks SqDancerLynn1, my chain was correct timing at very first before I screwed it up.. Well, now I have done already removing camshafts etc. So valve clearance adjustment in future isn't a big deal.

So, somehow the spark was not in condition. I installed a new battery, sparkplugs, caps and extra powerwire to to the coils. Now all the pipes get immediately equal hot at idle too.:-) Even with old original coils and wires!

Those electrical problems are sometimes so wierd!!](*,)
I tried to pinpoint the problem eg. swapping ignition wires, plugs, caps and coils. Measuring resistances and voltage etc.. Anyway there was always same two cylinders working fine and others did fail at least part of the time. That made me think carburetors needs cleaning although just the spark was weak.
 
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