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Discussion Starter #1
I just replaced my old Holley carb with a new Quick Fuel Technology carb. The car has a 302 with an automatic FX transmission.

What is happening now is that the transmission downshifts into low (not sure if it's 1st or 2nd) way too soon. If I'm going along and let off the throttle, once my speed reaches 30 mph the transmission downshifts. I didn't have this issue prior to replacing the intake manifold and carburetor. If I remember correctly the modulator on the transmission has a blue stripe was replaced somewhat recently if it makes any difference.

Can anyone offer any suggestions as to what might be causing this? Thanks.
 

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Make sure modulator has FULL manifold vacuum, AT the modulator, and there are no restrictions in the vac line.
Vac line should be steel line with SHORT rubber hose at each end.
NO full rubber line, it can collapse and cause issues.

Make sure kick down linkage is free moving and adjusted properly and has a return spring at the carb.

Edit; sounds like you may have connected modulator vac line to a ported vac connection at the carb? Not full manifold vacuum.
 

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Discussion Starter #3 (Edited)
Well, you're exactly right. The vacuum hose was connected to the timed spark port and not the full manifold vacuum port on the carb. Should have looked at the instructions more closely. All good now.

Thanks for your help, galaxiex!
 

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GalaxieX got it in one . Have seen that before. One thing I will add. Taking vacuum from those points , I have seen fuel get into the modulator line . Originally the modulator took vacuum from the rear of the intake , the correct way to run the vacuum hose was with the line routed upwards from the intake before it was fitted onto the steel line at the bellhousing.. That loop upwards was supposedly to prevent fuel getting into the line .

I suggest getting a small inline filter commonly used on mowers and motorcycles etc. . Put it in the vacuum line at the rear of the motor . Just shows is the vacuum line is staying clean :)
 

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I had one years ago , had a Barry Grant carb but vacuum was taken from the takeoffs as per the pic above . The modulator was full of fuel. Redid the line with a clear filter inline and the loop and has been ok since
 

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Discussion Starter #7
All good information. Thank you galaxiex and gregaust for your help and insight.
 

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The reason for the loop is to keep gas vapors from settling in the modulator and/or other lines.. If gas vapors find their way into your distributor cap, when you crank the engine, the cap will blow off.. Fairly uncommon in Fords....
 
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