'78 XS750 no start - popping and backfiring

[oldyam80sg]

Good job but don't keep using starter fluid. My boss at work had a Kawasaki Vulcan that burst into flames using starter fluid in the air filter.

[beard_thicc]

Good job but don't keep using starter fluid. My boss at work had a Kawasaki Vulcan that burst into flames using starter fluid in the air filter.

I'm not spraying it in the air filter though?? I don't even know why you'd do that. No offense to your boss, maybe h just didn't know any better.

I WAS spraying it in TINY LITTLE SPURTS into the carbs to test and make sure ignition was working.

But I'm now past that stage and trying to get it to run off fuel.

[beard_thicc]

SOLVED!!

The issue (or at least the main one) turned out to be that the harnesses for the #2 and #3 ignition coils were swapped. The previous owner said he had them off so he probably accidentally switched them.

I used this wiring diagram for reference, though on my bike where the wire is supposed to be green, it is grey instead:


The reversal was causing cylinder 2 to fire too late, and 3 to fire too early, which was why it was backfiring so spectacularly.

I hope this helps someone in the future! Check your wiring!

[Radioguylogs]

Wow - that is an unexpected cause.

Congratulations on solving it - even if it took a year!