Possible ignition problem?

[pablohoney]

hi,
I have a 1979 xs650 special with pod air filters, open exhaust with a small baffle, and a pamco ignition system. I went up one on the main and two on the pilot, and did nothing more. Here's the deal, it was running pretty good, then the bike was having issues which turned out to be a wire from the ignition plate rubbing then grounding on the ignition unit rotor. Pete sent me a new plate and it all ran fine until, one of the orange wires going to the coil got disconnected and destroyed the trigger and coil. I replaced the coil and put the old trigger on with the wire repaired. Now it starts and idles perfectly and runs great for a few minutes until the bike backfires through the intake and knocks the carbs off their boots. Before I buy a new trigger, does it seem likely that is the problem? The advance unit has new springs and seems fine. I bought the trigger about 1.5 years ago and when I got it, I had to file the plate down a bit to get it retarded enough, didn't have to do that at all with the new plate pete sent me. Seems weird. Thanks a bunch!

 

[retiredgentleman]

Are you using a timing light to check at idle and full advance?

 

[pablohoney]

Just at idle, what do you do if it isn't right at full advance?

 

[pablohoney]

Anybody?

 

[retiredgentleman]

The full advance timing is the most important, as far as preventing damage to the engine.

How old is your camchain? Perhaps it is stretched and needs replacement. You want to have the camchain adjustment correct before setting the timing.

Backfiring...................timing likely not correct.

If you can't get both the correct advanced and idle timing, the ATU bob weights are worn excessively. There is a mod (grizld1) that I use, or you can buy a new ATU.

Since I've had the bike, I realized the timing range of the ATU was too large. When set at the F for idle, the timing would go well past the fully advanced mark. This was not safe for engine longevity, so I would compromise by moving the idle timing towards the TDC mark. Not the best solution!

grizld1 had mentioned a few years back that you can adjust the advancer weights to bring it back into range by peening. I thought I need to try that, but never got around to doing it. Well, finally this spring I took the weights out and peened the little tangs on the weights. grizld1 was right as usual.

I found my tangs at 0.156". At first I only peened mine to about 0.161", but the timing range was still too expanded. OK, so I removed the weights again, and I decided that the answer is to keep peening the weights until there was a very tight fit in the slot in the "slotted disk". Yamaha made the slot in the slotted disk a specific size for a reason................it gives the correct timing range of 25 degrees (15 to 40 degrees).

So, I just peened some more and did trial fits until the tang fit in the slot was a very close fit but not too tight that it would bind. It ended up at 0.168". That's a 0.012" increase in width of the tang. Your bike may be different. Just peen and trial fit until you get that "tight" fit in the slot. My timing light now revealed I had correct timing at both idle and at 4000 rpm!!

Thanks grizld1 for a great tip...................a very simple fix.

 

[pablohoney]

I made a quick video here, I first set the timing with the weights secured with a rubber band to get the full retarded position. This video is with no rubberband, hows it look? Thanks

 

[retiredgentleman]

You should not need a rubber band.

The video at idle is extremely short, but seems to be correct both idle and advanced.

 

[pablohoney]

Ok, the manual said to secure the weights while checking idle.

 

[pablohoney]

Didn't seem to be wandering a bit?