HRC_V4 Posted September 5, 2021 Author Share Posted September 5, 2021 The coil is from MG Cycles, I am betting a 3 ohm, going to check it. I will pull the plug wires and caps and check them first, I am going to smoke a 8 lbs butt today, so I will have some time to work. The jumpy tach makes me think coil, also, when something runs well for about 10 minutes then starts to get flaky I normally think electrical, it heats up and fails. Several local parts places have coils that will work, so if I need to, I will go get one, might order a Bosch Blue for the future, or just not leave the d@mn key on so long while chasing gremlins... 1 Link to comment Share on other sites More sharing options...
HRC_V4 Posted September 5, 2021 Author Share Posted September 5, 2021 Now I am really confused... The coil is 2.8 to 3 ohm across the + and - terminals, about 8.5k from either + or - to the cable out to the distributor. The resistance of each plug wire with cap is about 4.5k ohms, and they have 5k ohms printed on the caps. To me that is all close enough to what it should be that I think it is OK, although once in use and hot those may change and cause my issue. Now where I am struggling, on the distributor cap, both wires out to spark plugs are no resistance from out to in on the cap itself, but from the coil (center hole) to the spring loaded button I am getting resistance from 30 ohms to 50+ ohms, and it bounces around, even if I try to hold it in the same position. If I pull the spring and button and out and just check just the cap, there is no resistance, so all the resistance is in the spring and button. So I took my old cap and looked at it, old and dirty, but no resistance to the plug wires, but 1.2k ohms in the center hole to the spring and button. I pull the spring and button out and it is the same, so it seems resistance is in the cap itself, and it is very consistent when pushing the button in on the spring, or it is too low to be picked up based on the resistance in the cap. I will keep playing with it, I might swap spring and buttons and see what that does. 1 Link to comment Share on other sites More sharing options...
HRC_V4 Posted September 5, 2021 Author Share Posted September 5, 2021 I found my old coil and measured it, only 1.5 ohm between positive and negative, so no good, found a new coil for an agricultural project that measured correct, so I installed it. I also put the spring and button from the old cap in the new cap and that got resistance down to 10 ohms and much more consistent. Put it all back together, fired right up like it always does and she ran great for about 10 minutes... Then back to pop and stumble, so I checked plug wires while hot, they dropped a touch to 4.2k ohms, still not bad, checked the coil to points, 0 resistance, no issue there, coil to distributor cap, about the same, so no issue there. Only thing I can think of now is the condenser/capacitor for the points, I may run to the parts store and pick one up for a 76 VW Bug and put the right connector on it and see if that helps, I am to the point of throwing parts at it... 1 Link to comment Share on other sites More sharing options...
HRC_V4 Posted September 5, 2021 Author Share Posted September 5, 2021 This issue is definitely in the ignition system, I put a spark tester on it as well as my chainsaw tach, the spark tester showed spark get inconsistent as the RPM picked up on the left cylinder as it ran on the right, the bike would not run on the left cylinder other than start and idle, but even then you could see some inconstancy in the spark, the chainsaw tach showed pretty much the same thing, wild fluctuations in RPM while the bike was missing but staying about the same rpm. I even cleaned the old cap and put it on and it acted just the same. I think parts store run for a condenser to see if that helps. Link to comment Share on other sites More sharing options...
80CX100 Posted September 5, 2021 Share Posted September 5, 2021 7 minutes ago, HRC_V4 said: I think parts store run for a condenser to see if that helps. If there's a selection of condensers available to you, you may want to go with a name brand or made in a country with a reputation for better quality control, higher price? etc. I've read that some of the new off shore replacements are poor, and a 50/50 coin toss if they'll work. fwiw good luck 1 Link to comment Share on other sites More sharing options...
HRC_V4 Posted September 5, 2021 Author Share Posted September 5, 2021 1 hour ago, 80CX100 said: If there's a selection of condensers available to you, you may want to go with a name brand or made in a country with a reputation for better quality control, higher price? etc. I've read that some of the new off shore replacements are poor, and a 50/50 coin toss if they'll work. fwiw good luck I'm going to have to order a Bosch off the interweb, might get a blue Bosch coil at the same time just to have, but... SUCCESS!!!! Chased my tail for a $10 part that I can't test... I just bought what they had on hand, made in Taiwan, maybe better than Mexico or China, not sure, but after putting the right end on it, she fired up and ran great. Let her run on the lift for a while, sounded good, I think the idle has picked up a little, after about 10 minutes of that, out on the road. Last time it was the second climb up the hill where she started to miss, this time she did fine, even rode down to a buddy's house and then back, maybe 5 miles, but that is 4 more than last time. I will keep a spare condenser with the bike going forward and a small slotted screwdriver and an 8mm wrench, which may be in the tool bag. Now, about 2 more hours for the Boston Butt and all will be right with the world, at least for me!!! Thanks for the help! 2 1 Link to comment Share on other sites More sharing options...
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