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Holley j tube question |
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Cyclone 
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Joined: March-29-2018 Location: Usa Status: Offline Points: 32 |
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 Topic: Holley j tube questionPosted: January-07-2019 at 12:07pm |
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I never paid much attention to jtube construction but I got to wondering why there is a square hole in the inside radius of the tube. I did a search here and elsewhere and came up with no answers.
Thanks for any help |
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baitkiller
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Joined: October-11-2011 Location: SW Florida Status: Offline Points: 1693 |
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Posted: January-07-2019 at 8:18pm |
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kinda like the serial numbers on a condom.
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Jesus was a bare-footer.............
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Gary S
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Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Posted: January-07-2019 at 10:50pm |
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My guess would be that if that hole wasn’t there the speed of the air flowing through the carb throats would create a vacuum and drain the fuel out of the bowel via that J tube
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KENO
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Posted: January-08-2019 at 8:14am |
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My guess would be that Gary's guess is right.
If you're familiar with jet pumps, eductors, air ejectors and how they work , it's the same principle. High velocity air passing by that tube end and going through the venturis would create a low pressure in the fuel bowl. The hole negates this effect. It would be like trying to suck water thru a straw with a hole in the side that allowed air into it. In a 600 cfm carburetor, let's say you have 300 cfm of air going by the end of each tube, That would be quite a suction on the tube and the bowl if the hole wasn't there. |
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baitkiller
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Posted: January-08-2019 at 12:43pm |
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But the bottom of that tube is not submerged unless in a flooded condition. But I agree the negative pressure would (could) do odd things to the fuel level which is fed at what ~4psi?
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Jesus was a bare-footer.............
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KENO
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Posted: January-08-2019 at 1:17pm |
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But the tube doesn't need to be submerged to affect the pressure in the bowl which will in turn affect fuel flow thru all of the metering systems as bowl pressure is lowered.
With enough vacuum the tube will suck some small amount of fuel through it even if it isn't submerged I think we agree, the hole negates these issues. |
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baitkiller
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Posted: January-08-2019 at 1:47pm |
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Thats what I said, but you said it better
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Jesus was a bare-footer.............
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Cyclone
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Posted: January-10-2019 at 2:55pm |
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Thanks for the info, the hole makes sense to me now
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