Only firing cylinders 2 and 3 - Timing off?

[Guest]

Hi,

I have a '81 GS550L and got the bike running this morning after installing a Dyna S ignition and rebuilding the carburetors.

I noticed that the bike only runs on choke and dies with throttle or when I take the choke off and decided to check the plugs.

Only plugs 2 and 3 have any kind of soot on them, while 1 and 4 have no soot.

Is this a problem with the timing? 1 and 4 are not firing at the correct time?

I am new to all of this so sorry if this is obvious.

Thanks,
Kyle

[Rich82GS750TZ]

first I’d pull those plugs, plug them back in to their caps and one at a time, touch the threads against the engine as you crank. Should see spark. if you do, problem is likely fuel/carbs. If you don’t see spark....

1 and 4 are fired by the same coil, so I’d look at the voltage in from both wires to and at the front of that coil and the voltage out of both HT leads from the coil at the plug caps.

did the bike run before? What changed? Did something happen to cause the timing to be off?

[kylekochan]

Was running 6 months ago but throttle cable broke and decided to call it for the winter, took some parts off the bike to re-paint. Emptied the carburetors immediately in the winter and rebuilt them recently with a kit as the jets were all stripped. Then added the Dyna-s recently as well. Today was my first time starting it since the winter.

I've checked for spark as you said earlier and all 4 plugs were giving spark.

I will check the voltage as you say soon.

[kylekochan]

I just checked the timing as well. If I'm correct, the timing marks from left to right go TDC, Firing, Fully advanced? So if I rotate the engine clockwise, I would go fully advanced, firing, then TDC according to the fixed mark? So when I attach the test light and I rotate clockwise in that order with the advance magnet fully turned clockwise, I get the light to turn on at fully advanced. I have the same situation if I move the test light to 2-3 and rotate the engine 180 degrees from the fully advanced symbol on 1-4.

[Rich82GS750TZ]

High tension leads or high tension cables or spark plug wires or spark plug cables are the wires that connect a distributor, ignition coil, or magneto to each of the spark plugs in some types of internal combustion engine.

So you have spark. I don’t see a need to measure the voltage. I’m sure there’s a way to measure it, I’m not sure exactly how you would now that I think about it.

you say not soot on 1 and 4 plugs, those cylinder could just be running lean? but are you certain those cylinders not firing? Are those exhaust pipes cold?

If their cold this would lead me to believe your issue is more fuel related than spark.

[tom203]

Double check your dyna-s connections...since it was running 6 months, it’s likely related to the new ignition. Don’t hesitate to call dyna about your issue

[kylekochan]

I have nearly 400mV at cylinders 1 and 4 and 0 at 2 and 3 out of the HT leads, with 10V going into both coils.

Does that make any sense since cylinders 1 and 4 aren't firing and they have voltage out the HT leads?

Edit: I think this would make sense depending on what position the engine is turned over to?

[kylekochan]

Yes, they're cold to the touch when I can feel 2 & 3 hot. I just checked the float bowls and 1 and 4 both have fuel in them.

[salty_monk]

10v little low but shouldn't stop it running. If you have sparks on 1-4 and the timing is right (just follow the Dyna S instructions) then I imagine your pilot circuit is blocked or something else in those carbs you just rebuilt...

Did you get the KL kits? Those don't get much love round here...

[kylekochan]

How would I check if my pilot circuit isn't blocked? If my cylinders 2 and 3 are firing, would I theoretically be able to unplug the spark plugs, turn over the engine a few times and all of my plugs should be wet with gasoline?