No spark on cylinders 1 & 4

[eternal]

Okay guys, I'm starting to pull out my thinning hair on this one. I'm trying to get my '78 GS 550 running but there seems to be something wrong. I've replaced the coil, done the coil relay mod and still am getting no spark on 1 & 4. I've tried checking continuity from the coil to points- all seems good there. I'm getting 11.7 V input to the coils and both coils test out as functional.

Anybody out there got a bright idea about what I'm missing?

[rustybronco]

first questions... what are the resistance measurements of the coil primary side and the plug cap to plug cap on the secondary side of the coil?

[Dave8338]

Okay guys, I'm starting to pull out my thinning hair on this one. I'm trying to get my '78 GS 550 running but there seems to be something wrong. I've replaced the coil, done the coil relay mod and still am getting no spark on 1 & 4. I've tried checking continuity from the coil to points- all seems good there. I'm getting 11.7 V input to the coils and both coils test out as functional.

Anybody out there got a bright idea about what I'm missing?

How is the battery? Fully charged? 11.7 V should be enough to make the coil fire... is the ground / mounting point clean to bare metal and free of paint?

[rustybronco]

a shorted condenser is a factor... one step at a time...

[Texas Don]

I think rustybronco is on the right path. A shorted condenser would be my logical choice. Or you could have a set of points bridged due to arcing caused by a shorted condenser. Take the point cover off and put a wrench on the end of the crankshaft nut and rotate it clockwise. Observe the points opening and closing. There are various devices made to check capacitors, but you probably don't have one. Besides, it's less expensive to just purchase a new condenser and put it in the circuit to see if it fires.

[rustybronco]

swap the condensers... it's cheaper!

still point contamination, pitting, mal-adjusted, ect are other areas that need to be explored.

[flyingace]

Swap the coils - this will effectively split the problem in half. If 1&4 continue to be the problem, it's upstream of the coil (points, condensor, etc.). If it changes to 2&3, it's the coil or the plug caps/wires.

[mike_of_bbg]

If the coils test out OK and you'd like to keep the bike for a length of time, I'd suggest getting a Dyna S ignition and forget all about those points... $130 or so now but a lot less headache going forward.

[eternal]

Thanks...

I've had the coils bench tested, they are operating normally. I like the condensor option. Cheap enough to replace without breaking the bank. If it works, great. If it doesn't, they probably needed replacing anyway.

E