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1980 GS850 GT - ignition timing issue

J

John Eldridge

Forum Newbie
Hi everyone,
My bike won’t fire up after a rebuild. It was previously running (albeit a bit rough).
It’s getting fuel because unburnt petrol is collecting in the exhaust pipes.
I have strong spark on all 4 cylinders.
It backfires so I’m assuming it’s a timing issue.
I’ve re-checked the valve timing
  • The cam chain is properly positioned (20 pins)
  • All valve clearances are within spec
I’m thinking there is a problem with the signal generator.
Does the photo below look right?
In the photo, the T mark for cylinders 2 & 3 is lined up exactly but the arm on the rotor is well past the pick-up coil. Doesn’t this mean the cylinder is firing before reaching TDC?
This would account for the backfiring wouldn’t it?
Resistance across the blue and green wires from the signal generator is 304 Ohms (spec is 250- 350).

Any help would be appreciated, thanks JE
 

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    signal generator (Custom).jpg
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I had a most impressive backfire when I stupidly cross-wired the 1/4 and 2/3 coils.
 
Just to double-check your cam chain pin count: It is NOT 20 pins between the cam marks. Pin #1 is NOT over the mark on the EX cam. The pin that is directly over the EX cam is Pin 0, THEN you start counting. Pin #20 will be over the mark on the IN cam.

It is disturbingly easy to be off by one pin if you mis-iinterpret the counting instructions.

.
 
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