I do understand that.
not trying to insult your intelligence here, however, the carb had zero evidence of even being dirty.
Been doing this alot of years and cleaned many carbs with great success.
The evidence the carb is NOT clean would be the occasional backfire you're writing about. Not clean, or not adjusted properly. Take your pick. It's lean, one way or the other. It's not getting enough gas through the idle jets. No clue what this carb looks like, but would add that this COULD be a leaking o-ring as well. This would allow carb vacuum to leak by it instead of pulling (enough) fuel from the float bowl.
You wouldn't be the first one with tons of experience to have a carb humble you. I would include myself in that group.
I generally prefer to work on Honda's only, and then just 40-90hp models. So I'm very specialized - and I STILL occasionally have to go back through them for something or another that's not right.
My advice for an advanced carb guy would be to start at the tiny jets in the carb throat (by the throttle plate) and follow the fuel flow backwards to the float bowl, looking for any potential blockages or vacuum leaks. That's how I do the ones that are kicking my butt.... -Al
