The bigger picture - help me troubleshoot ignition problem

marshall

Hi guys,

I'm making progress on this gremlin, and I'd appreciate some guidance!

1978 SE, stock.

Right cylinder's been missing erratically. I followed Ferrell's Shadetree instructions (on 650central.com) to diagnose whether the problem was from electrics or fuel, and the results said: electrics. Great! Er... what next...?

Now with the left side missing erratically I started moving pieces of the ignition system back to the right side, one piece at a time.

Swapped coils, left -> right = left cyl still misses
Swapped plug wires, left -> right = left cyl still misses
Swapped plugs, left -> right = left cyl still misses

Deduction: those three parts are not the problem.

I assume this leaves the points and timing settings as possible culprits. Is that what I should check next? I'm assuming condenser doesn't come into play since there's only one for both cylinders, and this problem moves from side to side when I cross the ignition.

Points are gapped at about .35mm. And I don't have a timing light.

What would you do in my shoes? Smile

-marshall

jayel

marshall wrote:

I'm assuming condenser doesn't come into play since there's only one for both cylinders, and this problem moves from side to side when I cross the ignition.

Points are gapped at about .35mm. And I don't have a timing light.

What would you do in my shoes? Smile

-marshall

ah but there are two condensers they are just piggy-backed togather 1 wire is 1 condenser, the other wire is the other condenser, both grounding thru frame, switch just those two wires, problem move?

ask around, someone will have a timing light and people like to show and tell

Retiredgentleman

Make sure there is no oil film on the points. If the points and condenser are old, its best to just replace them. Also good idea to check the wires that run from the points up to the first bullet connectors. Put an ohmmeter on the wires and do some wiggle testing.

marshall

okie doke. still stumped! read on for details!

first, some data that might be helpful which I left out of the first post: the cylinder miss is only noticeable at idle.

I applied the suggestions given above.

swapping condensers did not move problem (glad to know there's 2, however!) After that, I replaced the unit anyway since I had never done so since owning the bike. so now, new condensers.

checked continuity from points to the first bullet connector, and ohm meter said ok. I also closely examined all bullet connectors between points and coils, squeezing them a bit tighter w/ pliers so the bullet really 'snaps' in there and has little to no play. [sidenote: Bike's wiring harness is roughly three years old, from MikesXS.]

then I installed a new point set on the offending side, gapped to .016. still no dice.

other bits of fiddling and/or calibrating that I've done since last post:

* adjusted cam chain (got rid of that ticking / rattling sound I've been wondering about)

* gapped both point sets to spec

* set static timing using multimeter (each point set opens just as the rotor mark crosses 'F')

Sooo... I'm still stumped. At this point I have tracked the ignition system from the cylinder all the way to the points, and can't isolate any offending part. But when I swap the while firing system via the method I mentioned before, the problem sure enough moves side to side. What gives?!

Overall the bike is running a bit smoother and sounds better (after cam chain tightened), but there is still a definitive miss on one cylinder every few seconds, lasting for a few seconds.

jayel

try some new plug wires or move only plug wires and caps and then the caps themselves, if you have resister caps could be a bad resister in it

marshall

I did swap caps w/ wires during the first round of fiddlin' (in the 1st post)

I see that I didn't mention that.

What Happened to 650rider.com?

Yamaha xs650