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Sorry to bump this thread, but for the sake of anyone having similar problems as well as to give credit to a great suggestion here is an update:
First took off the float bowls and soaked+sprayed the main jets, and anything I could access on the bottom of the carburetor got a good shot of carb cleaner.
No change.
Then I inspected the fuel line and found a very subtle pinching turn. Replaced the fuel line, routed it better and the power came back! Smooth throttle response again. Top winning suggestion was given by bonanzadave and chuck hahn.
The backfiring and lean looking plugs were still there though...
so I inspected the previously sealed airbox and found a few sources of air leaks. I resealed the whole thing, and reseated the intake boots (which are new in the last year, still very "rubbery" and no doubt form a good seal). All air leaks plugged. A very subtle change in the spark plug color, just a very faint, almost unnoticeable tan dusting tells me it's richer than the pure white it was before, but still too lean. There's also still popping upon deceleration/engine braking, though much less than before I sealed the airbox. I still think it's possible that my carbs were unknowingly tuned to compensate for the extra fuel coming from a leaking petcock, so when I finally replaced it these problems logically began. I think I need to adjust some screw on the CV carbs, but I'm not sure what, or how much I need to adjust. If I cannot figure it out with the search function, I will post something in the carb/fuel/exhaust forum, as I think that's where this might have belonged in the first place.
Thank you to all who helped!
First took off the float bowls and soaked+sprayed the main jets, and anything I could access on the bottom of the carburetor got a good shot of carb cleaner.
No change.
Then I inspected the fuel line and found a very subtle pinching turn. Replaced the fuel line, routed it better and the power came back! Smooth throttle response again. Top winning suggestion was given by bonanzadave and chuck hahn.
The backfiring and lean looking plugs were still there though...
so I inspected the previously sealed airbox and found a few sources of air leaks. I resealed the whole thing, and reseated the intake boots (which are new in the last year, still very "rubbery" and no doubt form a good seal). All air leaks plugged. A very subtle change in the spark plug color, just a very faint, almost unnoticeable tan dusting tells me it's richer than the pure white it was before, but still too lean. There's also still popping upon deceleration/engine braking, though much less than before I sealed the airbox. I still think it's possible that my carbs were unknowingly tuned to compensate for the extra fuel coming from a leaking petcock, so when I finally replaced it these problems logically began. I think I need to adjust some screw on the CV carbs, but I'm not sure what, or how much I need to adjust. If I cannot figure it out with the search function, I will post something in the carb/fuel/exhaust forum, as I think that's where this might have belonged in the first place.
Thank you to all who helped!
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