Ignition problem

[750hopper80]

I have a 1980 suzuki GS750. It has 2 coil packs, one runs cylinders 2 and 3, one runs cylinders 1 and 4. Cylinders 1 and 4 aren't firing. I used a multi meter to check voltage at the 2 terminal plugs for each coil. The coil for cylinders 2 and 3 read 10.5 volts on each with the ignition on, the coil for cylinder 1 and 4 reads 10.5 on one terminal and 1.5 on the other. Also with the coil unbolted and the ignition on the mounting bolts become magnetic. I bought a new coil and got all the same results. Any help would be greatly appresiated

[koolaid_kid]

Hopper, you need to go to BassCliff's site and run the ignition tests he has listed there.
Your ignitiion has 3 parts: the coil packs, the igniter (often mistakenly called a CDI) and a signal generator. You need to test all 3 parts before you start in parts replacement mode. As you have discovered, parts replacement mode can be very frustrating. If the igniter or signal generator is faulty, I suggest getting a Dyna S and be done with it. A very popular item around here, and much cheaper than replacement OEM parts.

[mike_of_bbg]

I believe that on the early factory electronic ignition only one coil is grounded at a time (the coils fire by having their grounds pulled). For the un-grounded coil your multimeter is completing the circuit, so you'll see roughly the same voltage at both sides of the coil. On the grounded coil you see the voltage drop across the coil.

Clearly you do have enough voltage loss to be problematic. The current to the coils has to pass through a few connections, and any of those could be dirty causing your voltage loss. The ignition switch itself is a common culprit. Many of us (myself included) have done the "coil relay mod": we use a relay to take current directly from the battery. The relay works just fine off of the lowered voltage to the coils.

That having been said, if you're still firing on 2 & 3 with the reduced voltage, full voltage will get you a fatter spark and probably easier starting, but probably won't make 1 & 4 start firing. +1 to Koolaid_kid that the Dyna S DS3-2 (~$120) is a good upgrade for the aging electronic ignitions in our pre-83 bikes.

You should use the ohmeter in your DMM to check across the secondaries of both coils. The coils themselves are typically ~14kohms, plus the resistance of the caps. Stock caps are ~10kohms, and the recommended NGK replacements are ~5k. So with stock caps you'll get a total of 30-35kohms, or about 20-25kohms with NGK caps. If it's much higher unscrew the caps and test them separately. When they go bad their resistance usually goes WAY up.

[750hopper80]

Thanks for the info. Went to Bikecliffs website and printed off a few papers to take to the shop. As far as adding pics i will try, at first it wouldnt let me for some security reason

[terrylee]

After doing all the test it would be good to do the relay modification for the coils, should be on Basscliffs' site also. terrylee