Perplexing No Start Saga '79 GS850. Requesting your help!

[Gorminrider]

Sure i'd agree carbs can atrophy over a winter but it's a bear getting them out and dissappointing if it doesn't help. .On simpller engines where your plugs are wet and your cylinders smell like gas and it's still not firing, it's pretty surely spark but on these more sophisticated engines, it's hard to get them to flood in that way by just turning them over with a starter.... so Gas down the plugs or if you can easily spray a dose a dose into the airbox inlets might do as well to see if further is needed..

[DesertRatliff]

Carbs are pulled. I'll be going through them again.

So that it's all fresh in my mind and since I have a working Dyna S ignition now, I'm going through everything again. With carbs pulled, I figured I'd spray starting fluid directly into the intakes. Bike doesn't start but I'm getting a backfire/afterfire out of the 3/4 exhaust. What could be causing this?

I've got:
-Ignition statically timed for 1-4 and 2-3 where it says is appropriate. Signal voltage is indicated at the F 1-4 window and the 2-3 window on the rotor.
-12+v to the coils at rest, 11+ volts to the coils while cranking
-Coils hooked up to the appropriate spark plugs
-fresh spark wires going to the caps/cut about a 1/2inch off of all four and re-attached to the caps
-new non-resistor NGK spark plugs on all 4 cylinders
-checked and adjusted valves to spec
-spark on all spark plug wires. Not what I would call strong spark, but I do have confirmed spark on all 4 cyl.

Why the backfire with an electronic ignition that's statically timed right, though? I'm scratching my head.

[rphillips]

I remember, years ago, I'd had my bike apart & when put it back together it wouldn't start. A friend helped me figure it out & I had installed something on the ign. backwards & the timing was 180 degrees out of time. I,m thinking maybe the spark advancer, I remember it was something very simple & easy to correct.. Just wondering if there's enough plug wire to swap the plug wires on 1 & 2, and on 3 & 4. pretty simple just to be sure it isn't 180 out of time. If this is stupid, just forget it, it's been 40 yrs ago & I can't remember for sure.

[DesertRatliff]

Thanks for posting. I've swapped signal leads to no avail but I'll try swapping the rotor orientation around. I thought I did it by the book but something about the firing order just can't be right

[DesertRatliff]

Only change with the pickup rotor swapped 180 degrees is a slight pop out of a carb instead of a backfire out of 3/4 exhaust. I'm slowly losing steam.

Glad my 1980 GS850 is running well as I've been enjoying that.

[Gorminrider]

spark on all spark plug wires. Not what I would call strong spark, but I do have confirmed spark on all 4 cyl.

They never are on my bikes. OR on a coil + plug just flickered on the bench using a 12 volt battery. It's not like a lawnmower or an outboard where they give an audible "crack" and light up a room ! Like due to a finer dwell and that they aren't running from magnetos. You can't see plasma? and..these MC run at fairly high compression too which affects ignition. These are my theories that apply to my well-running bikes. A visible spark is usually good enough

[Gorminrider]

I'm expecting it's the fuel supply (very common) ...you'd have to be making big efforts in your sleepwalking episodes to change the ignition parameters so much. But of course, fairies DO exist and they're pretty good with animals so they can easily get past your Guardian Critters. But it's not the likely thing from your descriptions...
with gas supply to even 3 out of 4 carbs, enricher on, it should go. NOTHING happening Points to petcock or (much less likely vacuum ; valves, timing chain, etc)

[DesertRatliff]

Thanks for your responses, Gorminrider. I do have confirmed spark on all 4 cylinders per your description. Also to note, for anyone who cares, when I go to start the bike, I've connected the coils directly to the battery with a fused lead to take the switching/relay/wiring harness variable out of the equation.

As for fuel supply, I thought I took that variable out of the equation when I sprayed ether into every combustion chamber, once from the spark plug holes, now directly into/past the carbs with the airbox removed. All I get is lots of cranking and then a very loud afterfire out of the 3/4 exhaust. Ear protection has become part of my routine now.

Other than timing, improper fuel delivery, etc. I've read that afterfiring can be caused by leaky valves. So I did a leak down test and have discovered that cylinder 3 is leaking (out of what I believe to be the cylinder rings) at about 9% (at 90psi, cylinder 3 leaks down to 82psi, audible hiss from when I open the oil fill/crankcase). Checked valve clearance again on that cylinder and it's in spec at .005. Buckets spin freely at TDC. The other cylinders are tight as a tiger and not leaking.

But even with that, it should still run on 3 cylinders, right? And I've never experienced smoke on start up in the dozen or so times the bike has run since I got it running again.

Yet I still I have nothing.

[salty_monk]

It would still run on 3. If the bike sat a long time expect those numbers to come back up with regular use. Probably a stuck ring.

Weak spark if it's not coils or leads or plugs (Have you tried turning it over in the dark? Sometimes splits you can't see allow the spark to "leak" to the head before it arrives at the plug, pretty easy to see at night) would say to me that something (probably coils or Dyna S) is wired backwards.

Also just to humor me... try running a totally separate temporary line to the power for the Dyna S. I had that problem once. I did the relay mod but the Dyna S was for some reason pulling the voltage way down. Putting it on a separate line (temp and then permanently) solved it.

[DesertRatliff]

It would still run on 3. If the bike sat a long time expect those numbers to come back up with regular use. Probably a stuck ring.

Weak spark if it's not coils or leads or plugs (Have you tried turning it over in the dark? Sometimes splits you can't see allow the spark to "leak" to the head before it arrives at the plug, pretty easy to see at night) would say to me that something (probably coils or Dyna S) is wired backwards.

Also just to humor me... try running a totally separate temporary line to the power for the Dyna S. I had that problem once. I did the relay mod but the Dyna S was for some reason pulling the voltage way down. Putting it on a separate line (temp and then permanently) solved it.

With your advice, I'm 25% of the way there!! Thank you, Salty!! As you suggested, I temporarily wired the (+) power lead to the Dyna directly from the battery and the bike started, although it appears to be running only on cylinder 4 right now. But it's a big start!! Especially considering I ran out of ether and have re-introduced the fueling variable again. I'm headed to the auto parts store to get more ether but will keep you all posted. I know you're all as excited as I am right now. Thank you thank you thank you! Just the lead I was hoping for.

[Grimly]

Well, don't over-do the ether as that kills engines.

[DesertRatliff]

I started all of this with a nearly empty can. Thanks for your concern and advice, though. I'll go easy on the stuff.

[oldGSfan]

I remember, years ago, I'd had my bike apart & when put it back together it wouldn't start. A friend helped me figure it out & I had installed something on the ign. backwards & the timing was 180 degrees out of time. I,m thinking maybe the spark advancer, I remember it was something very simple & easy to correct.. Just wondering if there's enough plug wire to swap the plug wires on 1 & 2, and on 3 & 4. pretty simple just to be sure it isn't 180 out of time. If this is stupid, just forget it, it's been 40 yrs ago & I can't remember for sure.

That reminded me, not helping here but an anecdote - I replaced the timing chain tensioner on my first car, it was the first real mechanical task I had ever did. I was 16. I put it 180 out of whack (18RC Toyota). Not so easy to correct, but I realized the distributor could be installed 180 out as well, so I did it. I wondered if the next owner ever found that out

[DesertRatliff]

I hope some of the "learning" I did on machines in my youth won't ever be discovered by the living! I've got a few of those stories myself and really hope this bike won't be cataloged with them!

[salty_monk]

Glad you've taken a step forward!