I have been working off and on and my 83 project bike since this time last year. I purchased it with a blown head gasket which I replaced. After I determined that the motor started and ran I noticed a bit of roughness at low speed, just off idle however I moved on and fixed up a few cosmetic issues. This year I replaced both tires, battery, plugs and brake discs. Changed all the fluids and added some ATF to the gas. At this point I started riding it in order to see if some of the roughness that I originally noted might just work itself out with some regular riding. Well after 100 miles it has not. Basically it starts and idles just fine, however if you open the throttle just a bit there is a stumble and slight miss right up through to 2000 RPM. When starting from zero under load you really have to work the clutch and the motor sounds like it is laboring just to get the bike going. It also makes that mechanical sound that you get when you are in too high a gear at too low a speed. Once you get into second and the revs up things smooth out however it still feels lazy all the way up to 3000 rpm. After that it wakes up and pulls fine up through the revs. When thinking about the problem I thought it might have a weak cylinder. I have yet to get my compression tester adapter to fit the hole so I was waiting to do the compression check before going any further however yesterday I tried to find the weak cylinder by unplugging spark plug wires one at a time to see which one had the least effect thinking this might point me to which cylinder was weak. I discovered something interesting. When sitting on the bike if I unplug either of the back two cylinders the bike starts and runs. Of course it has a full miss but it will start right up and go to a rough idle OK. However it I unplug either of the front cylinders and try to start the bike, it will not start at all unless I really work the throttle and it will not idle. It really sounds like it is only running on one cylinder at this point. So I remember reading here earlier that each coil runs a pair of cylinders. Front pair on one coil and back pair on the other coil? If this is the case I think I have a pretty strong indication that my rear cylinder coil is weak. Is this logic correct?? I have already looked at eBay for replacement coils. There are lots out there but most are used and they seem to come as a pair. Other then redoing the ignition system is there any other options for getting coils for these old bikes? The eBay route seems like a bit of a gamble. Thanks.