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Discussion Starter #1
Recently I've been trying to get Jenny's carbs dialed in as perfectly as I possibly can. I have the carbs synced with virtually 0 difference using a DIY water manometer. The engine evened out noticeably after the sync, but I was still getting symptoms of a lean condition. The engine was responsive and would rev freely, but was a bit rough low in the revs and I was getting loud pops on occasion when lurching in slow traffic under 3k RPM. I've also been running slightly hot; slightly over 3/4 in Minneapolis traffic on 85F days. Pulling the plugs confirmed.

Problem was, I had bought muffler gaskets from Caltric and, of course, received the wrong part which were larger. I'm impatient so I butchered them up to fit at the expense of a perfect seal. There was a noticeable exhaust leak at the H-box joint on either side. I guess that was enough to throw off the mixture and cause my issues. I managed to track down all new gaskets for the headers and mufflers and installed them. The result? I'm back in from 3 turns out to the 2 1/2 baseline (which previously brought on really lean symptoms) and running much more smoothly at low revs. The temp has settled closer to center under the same conditions, but I understand this cooling system doesn't like lots of idling anyway (stock camshaft fan). The pops I mentioned have stopped and the idle when warm has come down enough so that there isn't as vast a difference from cold to warm. It's also nice to not have the leaking fumes accumulating in my helmet.

I feel like I finally have a reliable baseline now to start fine tuning now that everything is back to spec. Although a bit anecdotal, I hope this will help someone else some day mingling among search engine results. She's running so well! What an astonishing machine; especially held to today's standards.
 

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It's a wonderful reminder of how everything in the chain of events beginning at the air filter and proceeding successively through to the backpressure of the mufflers is inextricably intermingled in cause and effect. Change any one thing; everything else reacts. Change any two things and check yourself into a psych ward. A good tale of how engineering works in the real world.

And, yes, since my Harley pipes have been imperfectly gasketed (i.e. bodged) and I'm puzzling a bit over the results of my plug chops, you have helped someone else, today. Gratitude.
 

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To get meaningful results from plug chops you need to drive steadily for several minutes then simultaneously disengage the clutch and cut the ignition, then coast to the side of the road and pull the plugs while they are still hot. If you slow down with the engine running deposits from idling will obscure the readings.

BTW: Popping in the exhaust after you close the throttle is the classic symptom of a leaking exhaust system. IIRC, it is caused by fresh air being drawn in and providing the oxygen needed to ignite unburned fuel that has collected in the mufflers.
 

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Discussion Starter #4
Yeah, for sure; the Clymer manual set me straight on reading the plugs before I went out. I think it's exactly what you described. The roads through the MSP airport were nice and vacant for doing this.

I think I only randomly stumbled across someone here mentioning exhaust leak popping in another post about an unrelated problem but it was vague and wasn't that member's problem.
 
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