Misfire on 1 and 3

[Guest]

Bikes an 82 GS1100G. I have checked the valve clearances, everything is good or only need minor adjustments to be back to factory settings. I then compression tested each cylinder just to make sure I was good and everything seems OK. I rebuilt the carbs and set everything the way it is supposed to be done, including a good bench sync then a vacuum sync once they were back on the bike (and the bike was warmed up) and everything was set good there. I then ohm tested the coils to make sure they were good power going to the plugs, per my Clymer manuals testing procedures and they are. I put new plugs in it and even set the gap with a micrometer just to be safe. Now in neutral I have an awesome sounding bike. The second you put it in gear and get past 2000 rpm, mo matter what gear you are in, I start to get a misfire. As far as I know, even after checking to make sure, the bike is completely stock. I only seem to get the misfire when in gear going down the road. I thought maybe it was a timing issue so I checked that and even played with it a little, advanced and then retarded the timing then set it back to stock, and ever thing seems perfect there. Again all this is done in neutral when the problem isn't there. I checked the points, gaps are good points are in good shape and again everything seems to be perfect. Then only other thing that I have done was plug off the vacuum line coming from the carb to the petcock and put in an inline fuel shut off valve. I had to do this because the diaphragm inside the petcock is bad and fuel flows, at normal running pace, no matter what and I don't like flooding the carbs when the bike is off. I have pulled the plugs and checked them after running the bike for a while, again in neutral when all the cylinders seem to be firing perfectly, and they are OK. I am lost now. Did I miss something? What else could I check, keeping in mind the bike runs like a beast in neutral and the problem is only when in gear going down the road. The season is still good and I really would like to put some more mile on it. Please help!

[rustybronco]

Do you recall what the secondary resistances were on the 1-4 and 2-3 coils?
What is the coloration of the spark plugs at tip,mid insulation and down deep where the insulator and outer shell meet? (good is not an answer)
Did you check the slide diaphragms for any holes or tears?
Did you verify that all jet sizes were correct?
Did you inspect the jetting for blockage through some sort of magnification?
How did you verify that the misfire was on cylinders 1 and 3?

[OldVet66]

Did you check your plug caps, they can break down when they get old. Unscrew each one, cut about 1/2" off each wire and screw them back on. I always started mine with an awl so the point screws into the center of the stiff stranded wire.

[adam]

Carbs are perfect. Jets are clear even under magnification. Jet sizes are all right according to Brenny's, they know their stuff so I used them to make sure. Spark plugs are nice and tan on the collar around the electrode. they are not wet and clean down in at the base of the inside (no major discolorations or electrode wear) and they are even gaped right. I have a nice healthy fat blue spark on every plug when cranking. I pulled the coils off again and this time did an primary and secondary ohm test with a multimeter. Primary on both couls is 4.0 ohm exactly. Secondary I cannot get a reading on either coil. Looks like I probably should start there. Any one know where I can get a set of coils?

[tom203]

".....Secondary I cannot get a reading on either coil. Looks like I probably should start there. Any one know where I can get a set of coils?"

you our got nice spark on all plugs, so your ignition coils are fine.
unscrew caps from plug wires, stick meter probes into plug wires, you'll probably get about 12000 ohms between them on each coil. The plug caps are deceiving to measure over.

[Brendan W]

I'd be looking for an air leak.

[adam]

No reading across any of the wires. I am using the 20K setting, I do believe that is the setting to use.

[adam]

No air leaks as far as I can tell. I used some older ways of checking like a can of spray cleaner to spritz the boots and around the carbs to check for a leak. If there was one there it would of changed the idle speed of the motor, either throttle up or down or die. Nothing happened. I also had a bike shop hooked up their set of vacuum gauges and I am pulling an even amount of vacuum across all the carbs. If there was an air/vacuum leak the carbs would never be able to be synced right. I also did a compression test and each cylinder is well over 100. After all this I then went to ignition possibilities and broke out the multimeter. Checked the points and timing to make sure it was sending a fire signal at the right time and it is, did this using the Clymer manual I purchased. Using the repair manual I bought I checked the CDI box for correct function (long processes there). CDI was good. Checked the leads going to the coils for damage and they looked ok and were able to carry a load. That's where the multimeter came in. Then proceeded to check plugs, according to my father in law after we cut up the plugs that were in it, they are all OK, not running to lean or rich. Keep in mind the bike will run like a dream, all the way up to 9000rpm, that means smooth and clean when not in gear. No hanging throttle or weird idling up or down and the response is fairly crisp for a 30+ year old bike. My father in law I do trust. Finally after all this I decided to test the coils. I am getting 4.0 ohms exactly on the primary set at the 20 setting and nothing on the secondary set at the 20K setting. I know it is possible the coils are not the problem but I ordered new ones anyway with new wires and boots. The old ones were a little rotted anyway and needed it. I know its missing on cylinders one and three because these are the cold ones, actually measured all the pipes about 3 inches past the first curve at the head and 1 and 3 measured about 80 degrees colder. They don't seem to miss all the time but about every other time. This could be an intermittent coil operation which would be really hard to find without a good set to swap them out with. We will see if the new ones fix it when they get here.

[JJ]

You have points on an '82 GS1100G? They came from the factory with electronic ignition.

[Brendan W]

Weird. I would try to make the misfire move to 2 & 4 by swapping over the ht leads on each coil. Spraying the leads with something like WD-40 can help if the problem is spark leakage.
It's just possible that you have a damaged wire somewhere that plays up when the bike is moving. Follow it back from the 'points'.

[adam]

Its alive, alive. New coils, wires, plugs, boots, and bit of a cleaning. Finally pulls this fat guy down the road again.
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