Re: 9.9 Johnson Carb Question

[Don]

quote outbdnut2:

I saw that bearing in the carb kit photo but with it sitting on the gasket, I wasn’t sure if that’s what it was – Thanks for clarifying. I’ll order the kit now – as a minimum, I know I need the welch plug I pulled out, and will now pull the bearing too now that I understand what/where/how, etc. of it. Meanwhile, I’ll borrow a carb from a 15 and try it.
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A couple of you recently mentioned the NGK plugs. I’ve got BZ7HS plugs in this one already, and have tried BZ7HS-10s I borrowed form a well-idling 15. I fixed several issues on another 9.9 a couple years ago and replacing the Champions with NGK plugs was like magic making it idle perfect, so I’m a believer.
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Yes – I always put a nut on the bottom of those recoils when I pull them – learned that fast first time I pulled one!
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An observation while sticking a wire through the holes below the welch plug: When the throttle plate is all the way shut, only one of the three idle holes into the side of the carb throat is downstream of the throttle plate, so the other two are not in use. Is this enough? or is something worn on the throttle plate where at least two holes should be feeding at closed throttle plate? The center hole is almost directly under the closed throttle plate actually being partially blocked by the edge of the plate.
Dave

Well, those holes are being used, but air is pulled through those two holes closest to the needle valve (due to low pressure in the mixing pocket) to help meter/emulsify the fuel properly….So, let’s just say you plugged the most forward hole, the engine would run rich at idle/throttle plate closed because you are blocking the air supply and forcing the carb to pull more fuel up through the low speed plumbing/passages to the mixing pocket…
But, now let’s think of what happens when you crack that butterfly just open a bit….Now, the two holes farthest from the needle valve are under low pressure and will be delivering fuel/air mix to the venturi.
Now let’s crack the throttle plate just a bit more, and all three holes are subject to low pressure and will be drawing fuel/air mix into the venturi.
So, let’s just say the hole closest to the needle valve was plugged. At dead idle, with the throttle plate closed, you would have a rich condition. Open the throttle plate a bit for off idle and you would have a lean condition…