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Have had ignition issues in the past, installed Twin Tech external module, to get away from heat in nose cone. Worked great, went for ride this morning got few miles and felt like cylinder cutting out and backfiring like crazy. Last work down was replacing seals in pushed tubes, will check push rod set up. Any ideas? Thanks in advance. Be safe!
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I had a similar issue with a 1980 Shovel head, (i bought it used from a good neighbor and friend). He had removed the speed O and tach, had some 8" tall risers installed under the drag bar clamps. (He was just a lit' guy) The only man i ever met that had to duck to walk in a garage door and i'd guess his weight at around 300 lb. ( While i was a 6' bean pole in comparison at 170 lbs.) (Why i give all these useless facts will make sense) :

I removed the risers from the bars and softened up the suspension as much as i could get away with. As the bike rode like a po-go stick with my skinny ass! Right after i made these changes the bike started giving me issues with backfiring.
Not the common de-cell pop, but on acceleration it would fire off like M-2 firing burst! Around town it would back fire once or twice (sometimes). I'd get it out on the super slab, it would run great (for about 20 miles). Then all of a sudden it would fire another M-2 burst whenever it felt like it. It didn't matter if i was just cruising along or making a rapid acceleration. It would throw flames out of those shorty drag pipes! I would pull to the shoulder in near panic. No matter what i did, i could not make it backfire when i wanted it to. ( Rap the hell out of it and back off while at the shoulder of the road) It just responded with "Well lets GO!" I would drop it into gear and pull back onto the highway BAM-BAM BANG- before i would get to third gear! (I very seriously considered taking it out back and shooting it, just to put it out of my misery!)
I can't even tell you how many times i / we checked and re-checked the timing, valve clearance, points (yes it had been converted back to points). Inspected every item on that bike, over and over again. It ran PERFECTLY in the garage... Bill (the friend i bought it from) would test ride the bike: All good, every time! (He's thinking i'm crazy by this point) That bike loved him but, it hated ME! I would throw a leg over the saddle and BANG! It backfired before i could pass his house (next door)... This time it just happen to be dusk.
Back into the garage, (with the lights off in the garage) Rev the hell out of it, snap the throttle back to idle, over and over.. finally it backfired in a controlled environment. This time i just happen to be looking at the bars when it did it. I saw a faint blue reflection of a spark as it backfired! Finally have a direction to look at! Started digging into the front end. Low and behold, found the culprit!

Way back when Bill removed the gauges (many thousands of miles ago), he cut the wire feeding the tachometer. He just let that wire fall into the neck. The bike didn't care. With his weight on the saddle, the bike was smooth as silk. But, put my skinny ass on it, that wire would rattle around in a constant search for a grounding point! A simple electric cap cured the whole mess!

To the OP, I seriously doubt this is the issue you are having! It was the biggest P. I. A. problem i have ever encountered on a M/C. I just had to share it. While it is related to your post.
 
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