Q Jet Carburetor Air Flow

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pamotorman
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Re: Q Jet Carburetor Air Flow

Post by pamotorman »

difference in Qjet CFM
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pamotorman
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Re: Q Jet Carburetor Air Flow

Post by pamotorman »

[quote="Geoff2"]I don't think the window in the seat adds any flow. The restriction to flow is the small 0.125" hole. If you calculate the area between the needle & inside wall of the seat [ whee the fuel needs to flow to get into the bowl ], it will be greater than the area of a 0.125" hole.

I do not believe GM would have spent the money to machine those windows if not necessary.
kimosabi
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Re: Q Jet Carburetor Air Flow

Post by kimosabi »

Well if the needle is tight enough in the seat housing to become a too big of a restriction the windowed seat certainly makes sense. I made sure feed problem is a non issue when I installed a surgetank with a Walbro pump in it. Would probably not have mattered if the seat was window or not in my case.
F-BIRD'88
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Re: Q Jet Carburetor Air Flow

Post by F-BIRD'88 »

All true about the air cleaner base profile shape and the lid and air flow amount and quality.
On the needle seat when you have 2 Qjets the fuel flow load is shared by the 2 carbs,, so...
But lots of good Qjet tech getting posted. All welcome.
tenxal
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Re: Q Jet Carburetor Air Flow

Post by tenxal »

You need to be very careful with needle and seat sizes in the QJets. Bigger is not better for several reasons. :wink:
F-BIRD'88
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Re: Q Jet Carburetor Air Flow

Post by F-BIRD'88 »

tenxal wrote:You need to be very careful with needle and seat sizes in the QJets. Bigger is not better for several reasons. :wink:

Yes you get better fuel control with the smaller .125" standard needle seat.
Modest fuel pressure is best too. You need volume (a steady supply) not pressure.
There is a .135" and a big .149" N/S but if you don;t need it you are better off with the small er stock N/S.
pamotorman
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Re: Q Jet Carburetor Air Flow

Post by pamotorman »

also make sure the needle tip has a blunt end and not pointy as the pointy one reduces the fuel flow thru the seat because some of it is still in the bore restricting the fuel flow
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