Correct, there is a very small vent hole that leads from the side of the carb (roughly where I tap with my finger) to the hole above the throttle butterfly valve that you can see in the video. When the engine is at idle (so the throttle valve is closed) or when the choke is engaged (so the choke valve is closed), airflow through the main intake bore is 99% blocked, and all of the air feeding the engine comes from that little vent.
I redid my zenith 2 carb, but when I adjust the acceleration stop, the engine dies before it stops pulling air from the main inlet. No matter how precise I adjust the idle control I did clean everything properly and all channels and needles are open. Did I install something incorrect inside? I did it according to the schematic
@@alexiskai ye so when I disengage the throttle stop bolt all the way, the engine dies? Even if I do it slowly and constantly adjust the idle bolt to try to keep it running. I remember when I disassembled the carb I noticed a little divot on one of the far edged of the butterfly valve. Is it possible that I installed it reverse and that divot should be near the idle hole?
@@DrTheRich On my Marvel carb, which you can see in the video, I still have about 5mm length on the throttle stop bolt, and my car idles at 400rpm, which is perfectly fine. You don't need to turn it out all the way. The important thing is that you're running on the idle circuit. You can check whether you're on the idle circuit by adjusting the GAV knob while the car is idling. If turning the GAV affects the engine in *any way*, you are *not* on the idle circuit. That's what I would look for. Get the idle as low as you can, verify that the carb is only using the idle circuit, and then move on to other problems.
@@alexiskai oh smart way to check. I'll do that when I have the engine back together. Could it be that because currently I have an enormous amount of blowby past the pistons, that it can't vaccuum powerful enough pull enough air through the tiny idle hole to stay alive? Also Is it possible for you to block the main air intake with your hand while idling and the engine keeps running?
@@DrTheRich I may have given the wrong impression in the video. The carb is designed so that a tiny amount of air will come in through the main inlet even with the butterfly valve completely closed. The valve isn't a seal - some air will still be sucked in around the edges. The important thing is that, when idling, the main inlet air does not get mixed with fuel. It's just air. Only the air that's coming in through the idle air vent, located on the outside of the upper casting, gets mixed with fuel. This fuel-air mixture then is sucked into the intake through the hole in the upper bore, right at the butterfly valve, that I point out around the 3:50 mark. As it enters the upper bore, it combines with the air leaking around the butterfly valve, which leans out the mixture slightly. This document is a good guide to testing the idle circuit and has some nice diagrams. www.santaanitaas.org/wp-content/uploads/2014/08/2OC-Zenith-Passageways.pdf
Hey, Thank You! I knew the adjustment was easy, I just didn't know how. Great Video. Thanks Again!
Steering column ordination, rotating the column at the steering gear box will change the spark control arm and throttle linkage position also.
Thanks for mentioning that. The car in the video has 7-tooth steering, so I couldn’t show that trick.
Correct, bent rods flex 100% of the time.
Awesome video.. exactly what I was looking for
Well done, thanks
Thanks!
At 3:35 It sounds like you are saying that the engine is getting air from somewhere else beside the air intake on the throttle body.
Correct, there is a very small vent hole that leads from the side of the carb (roughly where I tap with my finger) to the hole above the throttle butterfly valve that you can see in the video. When the engine is at idle (so the throttle valve is closed) or when the choke is engaged (so the choke valve is closed), airflow through the main intake bore is 99% blocked, and all of the air feeding the engine comes from that little vent.
I redid my zenith 2 carb, but when I adjust the acceleration stop, the engine dies before it stops pulling air from the main inlet. No matter how precise I adjust the idle control
I did clean everything properly and all channels and needles are open. Did I install something incorrect inside? I did it according to the schematic
Are you saying that the engine isn't able to run off the idle circuit at all? What RPM can you get it down to?
@@alexiskai ye so when I disengage the throttle stop bolt all the way, the engine dies? Even if I do it slowly and constantly adjust the idle bolt to try to keep it running.
I remember when I disassembled the carb I noticed a little divot on one of the far edged of the butterfly valve. Is it possible that I installed it reverse and that divot should be near the idle hole?
@@DrTheRich On my Marvel carb, which you can see in the video, I still have about 5mm length on the throttle stop bolt, and my car idles at 400rpm, which is perfectly fine. You don't need to turn it out all the way. The important thing is that you're running on the idle circuit. You can check whether you're on the idle circuit by adjusting the GAV knob while the car is idling. If turning the GAV affects the engine in *any way*, you are *not* on the idle circuit. That's what I would look for. Get the idle as low as you can, verify that the carb is only using the idle circuit, and then move on to other problems.
@@alexiskai oh smart way to check. I'll do that when I have the engine back together. Could it be that because currently I have an enormous amount of blowby past the pistons, that it can't vaccuum powerful enough pull enough air through the tiny idle hole to stay alive?
Also Is it possible for you to block the main air intake with your hand while idling and the engine keeps running?
@@DrTheRich I may have given the wrong impression in the video. The carb is designed so that a tiny amount of air will come in through the main inlet even with the butterfly valve completely closed. The valve isn't a seal - some air will still be sucked in around the edges. The important thing is that, when idling, the main inlet air does not get mixed with fuel. It's just air. Only the air that's coming in through the idle air vent, located on the outside of the upper casting, gets mixed with fuel. This fuel-air mixture then is sucked into the intake through the hole in the upper bore, right at the butterfly valve, that I point out around the 3:50 mark. As it enters the upper bore, it combines with the air leaking around the butterfly valve, which leans out the mixture slightly.
This document is a good guide to testing the idle circuit and has some nice diagrams. www.santaanitaas.org/wp-content/uploads/2014/08/2OC-Zenith-Passageways.pdf
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