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1&4 cylinders fire strong, 2&3 cylinders fire sporat

  • Thread starter Thread starter Anonymous
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Anonymous

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I just recently put the head back on my '82 GS750E. Everything went back together just fine and the timing has been checked twice. Don't seem to have any bent valves after the head was flowed and milled. When we went to fire her up, she wouldn't fire and it would backfire through the 1 & 4 cylinder. Tried looking at the timing again and everything matched up perfect. Then we did a spark test and found that the 1 & 4 cylinder had a good strong spark and the 2 & 3 cylinder's spark plugs would fire sporatically. Since this was a used engine, I went through and resoldered connections that looked corroded, old, etc. Still 1/4 were firing good, and 2/3 weren't acting right. Then I tried a spark test by switching the 2/3 spark plug wires to the coil for the 1/4 cylinders. Come to find out, the plugs that go into the coils for 2/3 were badly corroded on the end, and the ends for 1/4 cylinders were in great shape. I still decided to switch the wires on the coils. 1/4 were still firing strong, but 2/3 were still not sparking correctly. Am I to assume that it is just the corrosion on the ends of the wires, or is there something else I might be missing in the whole equation?
 
You could unscrew the ends and cut 1/2" off and re-screw the ends back on the wires and then check for spark. Or you can swap the pickup wires or ignitor wires and see if the problem moves to the other coil. If it does move then it's not the coil but a pickup/ignitor problem or bad connection somewhere.

or

set a multimeter to ohmsX1, unplug the ignitor from the pickups and touch the probes of the meter to the ignitor pins, you should see a spark on one coil as they touch and a spark on the other coil as you remove them.
 
Well, I picked up new wires and ends and got them installed this morning. I also switched the ingitor wires and spark plug wires on the coils, but that didn't seem to make a big improvement. But the new wires and ends seemed to make a little better improvement. Before, it seemed like the 1/4 cylinders were back firing. Now it seems like all the cylinders are backfiring at some point. One other interesting point to note, when I was using a spark tester that fit on the end of the spark plug wire to test for spark, I would get a spark when I turned the ignition off. This happens with all four spark plug wires. Is there something I am missing? It has an aftermarket dyna ignitor, aftermarket coils, and the signal generator doesn't have the blue and green wires running to it that the manual talks about. The signal generator has a red, white, and black wire that runs to the dyna ignition box, so I am kind of confused as to how to do the test with the multimeter.
 
I also forgot to add that while trying to start the engine up, it seems to pour a lot of gas out the overflow tubes. I also went through this morning and blasted the spark plugs since I didn't have time to run and pick new ones up this morning.
 
Sounds like you may have a couple things wrong with your bike. I would pick up an inexpensive multimeter (they are $3 on sale at Harbor Freight) with a 1x ohms scale and check the primary impedence on my coils and the secondary impedence. Since you have problems on two cylinders that are affected by the same coil, the coil is a likely cantidate for the problem. The impedence check will tell you if you have a short in the windings and the coil needs to be replaced. If you have a service manual it will tell you what the values should be and where to place the probes to perform these checks. In general, the primary impedence will be 1 to 3 ohms on most bikes and the secondary 15K-20K ohms. If you have readings other than what your manual suggests you should have, your coil is dead. Coils can sometimes work sporadically and may test OK once and then not the next time. This is the nature of a short. The innards of the coil is wire wrapped in plastic stuff and if wires touch (burned insulation) sometimes, they may not touch all the time. Dyna at http://www.dynaonline.com sells coils for your bike. Keep in mind that you will need two output per coil type coils and they need to be the corrected primary impedence. CDI type igntions use 1.5 (or something like that) ohm coils and regular electronic or points igntions use 3.0 ohm. If you use the wrong coils, they will tend to overhead quickly and fail.
 
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