Well, I certainly learned a lot about carbs over the last week. As mentioned previously, the H cylinder was barely running during the idle circuit but operated fine over about 1500rpm. I swapped the coils, the ignitors, tested the pick-ups, and replaced the plugs. No change. Then I balanced the carbs again. Nothing. Pulled the carbs, cleaned again, and cleared passages with compressed air. Verified my jets, checked all o-rings, and the diaphragm. Still wouldn't run on the H cylinder only.
I decided to broaden my web searches and start reading about the mixture screws since it was the only thing left to adjust. Eventually found a few posts on Triumph Rat regarding enrichening the carb until the idle starts to drop, then leaning out a bit. Interesting....
See, all my previous bikes that actually ran, were inline four cylinders and I always set them back to factory mixture settings assuming they need to be the same. Well, that's just not the case. I fired up the Duc, enrichened the H cylinder carb and I'll be damned, it worked. I could pull the plug wire from the V cylinder and it ran! I threw in some fresh plugs and went out for a ride.
Afterwards, the plug on the H cylinder looked about perfect, but the V plug was a bit rich, so I leaned it out about a quarter turn. I also noticed I have leaky valve stem seals. While that is supposed to be a quick and relatively easy job, it will have to wait until I pull the engine and do all the top end seals.
The other day, I reached out to my friend in CT, aka Mr. Wizard and asked for his input on what I had learned about mixture screws and if them being at different ratios was indicative of a carb issue. He said, most multi-cylinder bikes actually rarely have them all at the same setting! *MIND BLOWN* I guess my inline fours were just compensating enough that I never noticed. Crazy.
Never stop learning, and stay safe out there.
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