GS1000G - firing on all 4 plugs at same time

[Guest]

The heading says it all. I have now replaced the CDI unit with another unit and the same result. Anyone ever encountered a similar problem?

I rebuilt/rewired an 81 GS1000G recently. The old loom was removed and replaced with a complete loom from another donor bike. I removed old tape, checked for cracks and open wires before re-taping the loom again. All connectors etc. was left intact as they were still in good condition.

When I switched on for the first time, all lights, flickers, brakes, hooter etc. worked perfectly and all seemed ready to go. Trying to start, nothing happened except the occasional backfire.

Did all the checks for correct fuelling, carbs were properly cleaned etc. no problem so it seemed electrical. The long search then started and I eventually removed all 4 plugs, inserted them into their caps and grounded them all on the engine. I removed the cover of the pick up and using a 19 spanner turned the engine with ignition on. I got spark on all 4 plugs when the crank sensor arm passed the (1+4) pick coil up and the same when the sensor passes the 2+3 pick up coil.

Removed CDI unit, unplugged the one on my personal GS1000G and connected to the problem bike. Same result. I then ensured a 12V supply to the orange/white wire to the coils and bypassed the loom by connecting the black/yellow wire from the cdi directly to the coil and did the same with the white wire. Still getting the same result

Logic tells me it cannot be the cdi. I am stumped - any advice will be appreciated.

 

[Killer2600]

I removed the cover of the pick up and using a 19 spanner turned the engine with ignition on. I got spark on all 4 plugs when the crank sensor arm passed the (1+4) pick coil up and the same when the sensor passes the 2+3 pick up coil.

I would do this test cranking with the starter and see if the results are the same. The OEM ignition operates a bit different than the modern hall-effect based ones that most are familiar with. Running at speed is necessary for the pick-up to properly trigger the ignitor. That said, because your ignitor is being triggered and you tested two different ignitor units (what you called CDI), I don't think your problem is with ignitor function. Ensure the mechanical advance mechanism is free and functioning and then move on to other causes for a no start.

 

[Guest]

Problem solved. Do not know what the actual problem was but took out igniter, pick up, plugs, coils, all fuses, sprayed some q20 on all connectors, tested as per tests in manual and re-assembled. First turn it started and runs smooth. Now just for carb balance on then time for the road.

 

[dorkburger]

Not 100% sure, but I thinks these bikes ignitions are the "wasted spark" type, meaning that the plugs will still spark on the exhaust stroke.

 

[GregT]

Not 100% sure, but I thinks these bikes ignitions are the "wasted spark" type, meaning that the plugs will still spark on the exhaust stroke.

Correct - but only in pairs. 1-4 and 2-3. All 4 sparking at the same time is a wiring problem IMO. The OP's cleaning of all connections was the correct thing to do first.