340 Cyclone ignition issues

[toomanysleds]

I have a very low mileage '76 340 Cyclone that I am trying to get running. It only runs on one cylinder (pto side). When idling on the one cylinder, the rpm's will sometimes surge/pulsate. Checked compression and it's strong/similar on both cylinders. When I rest the plugs on top of the cylinders and pull it over, both plugs produce a nice strong spark. However, once installed the mag side remains cold (not firing). Why would it lose spark when under compression but have great spark just lying loose? I have switched the red & white wires to the coils and to the spark plugs (isolating the coils and cylinders one at a time) and it then ran on the mag side so I assume both coils are fine. The common denominator is that the cylinder that won't fire is which ever is connected to the white coil wire. My uneducated guess is a bad cdi box. Agree???? Is there a multi-meter test I can perform on the red & white wires? Is there any way to bring these cdi's back to life? I realize it's an old beast that has just been sitting around but it's pretty disgusting that a cdi box should fail with only 30 miles on it. I have read the FAQ section on cdi troubles but didn't see any testing values for this particular year/model engine. Any positive input would be appreciated.

[lwb140]

only 30 miles !!?? wow thats awesome wade

[harleysportster]

It takes more energy to fire a spark plug under compression. I would say the CDI Box is bad if you followed all the tested as outlined in the FAQ. There is no test for the CDI Box unless you have the original JD tester. Since you have an old machine, I would also replace the crank seals if they are original.
The 76 Ignitions were known to be bad out of the box so having only 30 miles is not unheard of.

[JDT]

If the machine only has 30 miles on it than the original seals are toast. At least to one on the mag side.

If the seal is out than it will not draw the fuel up through the transfer ports on that side and then it will not fire.

But It could be the CDI as Pat mentioned.

Replace both seals either way.