Holy Backfire Batman

[rtaylor522]

You guys can check out my other thread about 72 rebuild and brakes, but I've just gotten my bike running after a complete top end rebuild and carb overhaul....Overall things were going good, after 2 years of not running. Some leaking oil around base gasket on left side and thats it so far that was a major concern...
Anyways had been riding for about 2 miles and had bike running at idle for awhile before that. Just as I go to roll on the gas back down the street, The thing let out the 2 loudest backfires I had ever heard and quit....after some cussing etc. I pushed it back. After a few tries at starting, I'm seriously concerned...It continues to backfire and pop but no starting....prior to this it was a one start kick at idle all day.

I'm seriously at a lack of words for even where to start....I looked in the timing cover on the left hand side and everything is where I had left it with set screws tight, so nothing loose there.

This was so loud I'd believe it if someone told me I Holed a piston or blew a ring, but I have no idea what would cause this sudden death of my bike....AHHHH

 

[jay760]

Try looking in the right hand side where the advance is, to make sure it hasn't come loose

 

[ady66]

Check it hasn't blown the carbs out of the rubber boots when it backfired.

 

[Tech7]

Check all basics. Needs fuel, air, compression and spark. Don't overthink it. All 4 cycle engines work the same. Suck,squeeze, bang and blow.

 

[rtaylor522]

Okay guys...popped the right side advance cover and guess what...the locator pin fell out and the whole unit was loose.....ooops...gonna have to try and put that back together today. It's worth noting that I replaced the advance springs so those should be good...I'm just not sure why it came loose, but the whole thing was spinning freely with the locator pin riding around in the side cover.

I'll let you all know if it works, but i'm sure thats the problem...by the way, the carbs are still seated FYI but thanks for the reminder to check!

 

[TeeCat]

Okay guys...popped the right side advance cover and guess what...the locator pin fell out and the whole unit was loose.....ooops...gonna have to try and put that back together today. It's worth noting that I replaced the advance springs so those should be good...I'm just not sure why it came loose, but the whole thing was spinning freely with the locator pin riding around in the side cover.

I'll let you all know if it works, but i'm sure thats the problem...by the way, the carbs are still seated FYI but thanks for the reminder to check!

I wonder how in blue blazes that pin came out?! Thinking back to when I replaced my ATU, I can't imagine how that would happen, unless maybe the lock ring was really loose and allowed the plate to back off its seat.

Hope that's a fix!

TC

 

[rtaylor522]

Okay great news...bike is running...running poorly, but running. After re-assembling the ATU on the right side, I realized it came back from the engine shop installed 180 degrees off (i.e. the two line marks were'nt lined up, and the ring nut was'nt tight). So over time the ring nut loosened up and the unit popped out locator pin came out etc.

So when I reassembled ATU I put it together properly per the manual....guess what...still backfiring and not running.

Re-gapped points and tried to set timing but could'nt get it right. Well as I'm looking around I figured out that when we re-hung the engine we had the grey lead going to the left condensor and orange going to right side....exactly opposite of what it should be. Well Since I reinstalled the ATU the correct direction but the points wires were still reversed it was firing the cylinders at the bottom of the stroke isntead of the top, and on the wrong side.....swapped those two wires and re-seated my carbs since they decided to depart the boots during a backfire and guess what....started right up...

So I guess it was running by coincidence that the point wires were reversed and the ATU was 180 degrees off yesterday, but once I rebuild the ATU properly the points wires needed to be put back to the correct cylinders....weird sequence of events.

I think it's the original points on the bike and I am having a hell of a time actually timing this thing properly with the gap set....cant seem to tell what the widest point is to do the measuring and I cant get the right point into the adjustable range when the right side is at the "F" mark....not sure if they are just so thin and old that when gapped to .4mm that they can't close fully or something.

 

[jay760]

When you put the ATU back together again it pays to use loctite, I've had one take the end of the cam off!

 

[rtaylor522]

Ok...will do the loctite thing...btw just realized looking through a Pamco thread that I have that ring nut installed backward *lip in * so now I have to take that damn thing back apart....someone shoot me!