Alright you GS mechanical geniuses

[DrDoot]

I believe I've narrowed down my "not starting when hot" problem to the ignition coils. I have a replacement, but one of the spark plug caps has been cut off. Can I replace that with any spark plug cap, or does it need to be very similar/specific to my GS550? and what's the best way to splice it on to the coil?

[onchiman]

The original caps are NGK and simply screw onto the end of the plug wire. If you have enough wire left to simply screw on a new cap this is the easiest fix. If not, then you'll have to somehow remove the wire from the coil and fit a new wire and cap. Since this is epoxied in, heat may help loosen it up.

[DrDoot]

Alright, I got the other coils on, no starting though. I've now replaced both coils and the ignitor.

What else could be heat sensitive? (bike runs fine when cold, dies and then won't restart when hot)

[jonr]

Is the starter turning slow or do you get nothing at all?

J

[DrDoot]

Starter turns fine.

[jonr]

I know it sucks pulling plugs when the head is hot, but have you pulled each one out after it was hot and grounded the plug to see if there is spark? Don't do this near the spark plug hole by the way - there's a chance you could ignite the fuel.

-jon

[DrDoot]

I pulled one from each coil and couldn't see any spark while grounding against the cooling fins of the engine.

[koolaid_kid]

Actually, if you had a spare plug you would not need to pull a hot one, just use the spare plug and ground it to check for spark.

[jonr]

I know you stated that you replaced the ignitor, but if none of the plugs are firing, then I would suspect that the coils are not getting the signal to fire or that the coils are not properly grounded. I doubt that since you said you just swapped those out too. Are you 100% sure the replacement ignitor is good?

J

[DrDoot]

No, the replacement ignitor is from a parts bike. BUT, it doesn't matter which ignitor is on the bike, it will still die and not start again at about 10 minutes into running. I doubt that both ignitors would be partially bad in just the same way, but I can try testing one/both of them.

[jonr]

Doot,

You've got me stumped at this point. Your theory of it being heat-related seems right on, but where to go from here? Sorry I could not be of more help.

jon

[DrDoot]

Yeah I know what you mean. I'm reduced to mean looks right now.

[Nessism]

Well...if you are sure there is no spark when warm...and you have confirmed the ignitor is okay...next thing to check is the ignition pick-up coils, or points, on the right end of the crank. I'm not sure how to test off the top of my head but that's what I'd look at next.

[t3rmin]

I haven't got all the bugs worked out yet, but I'm having much better luck with my Dyna S system than I ever had with the stock ignition. At $120, it's cheap insurance against another stock igniter or signal generator failure down the line, too (assuming the Dyna is in fact more robust). And eliminating the igniter makes me hopeful that troubleshooting in the future will be much less of a headache.

[DrDoot]

What I don't understand is, that if it's a heat issue, I can plug in either of my two ignitor's when the bike is misbehaving, and neither work, but when it's cold, both work. This and the fact that both have the same thing happened when the bike starts and warms up. I will test, but don't think both ignitors are bad.