pump to carb line

[Mike Szadaj]

1968 Coronet RT. Gas line is 3/8 from tank to engine bay. Should the small line that screws into the carb also be 3/8? It seems the line I have is smaller, so it won't attach to the carb because the fitting is too small.

 

[Lionized]

1968 Coronet RT. Gas line is 3/8 from tank to engine bay. Should the small line that screws into the carb also be 3/8? It seems the line I have is smaller, so it won't attach to the carb because the fitting is too small.

I would say (with some degree of certainty) yes, if your tank feed line is 3/8" the pump to carb line should also be 3/8".

 

[OKDart]

I don't know what the factory came with, but the aftermarket ones available are 5/16" that I've found.
Also, from my hydraulic system experience, the supply line to the pump is always bigger than the output pressure line. Not sure if that theory applies to auto fuel systems though.

 

[RJRENTON]

I don't know what the factory came with, but the aftermarket ones available are 5/16" that I've found.
Also, from my hydraulic system experience, the supply line to the pump is always bigger than the output pressure line. Not sure if that theory applies to auto fuel systems though.[/QUOTE

OK,
I concur wholeheartedly. Usually the pump's suction line is larger to reduce the line loss or restriction. On my RS23V0A GTX, the pump suction (inlet) is 3/8", After the pump to the vapor seperator is 5/16" and 5/15" thru th3 all the carb's fittings. There is a 1/4" line from the vapor seperator back to the tank. The vapor seperator has a 0.060" diameter restriction on the 1/4" connection.
Bob Renton

 

[Mike Szadaj]

Here is what I did. I bought a short piece of 3/8 line with flares and threaded nuts on each end. I cut off one end, then bent the tube. I put a small flare on the cut off end, and hooked it up with rubber tubing. When you go from a larger pipe, tube, furnace duct, etc., to a smaller one you reduce the volume and increase the pressure. I don't want more pressure to the carb, I want to maintain volume. Make sense?

 

[RJRENTON]

Here is what I did. I bought a short piece of 3/8 line with flares and threaded nuts on each end. I cut off one end, then bent the tube. I put a small flare on the cut off end, and hooked it up with rubber tubing. When you go from a larger pipe, tube, furnace duct, etc., to a smaller one you reduce the volume and increase the pressure. I don't want more pressure to the carb, I want to maintain volume. Make sense?

View attachment 812597

Mike S,
Your premise is almost correct. Yes there will be a small volume loss but pressure will recover after the size change. The pressure is static as determined by the pump. Any losses will be insignificant when in operation as far as volume increase and pressure decrease.
BTW.....the carb appears to be an original CARTER AVS. Out of curiosity why are you NOT using yhe PCV system? The Carter carb was calibrated to use the PCV system (idle, off idle transition circuit and to dome degree primary main fuel system). Plugging the PCV inlet at the carb will result in a rich idle and off idle transition circuit. Plus the obvious benefit of reducing the moisture in the engine thru the PCV's purging.
Just my opinion of course.
Bob Renton

 

[Mike Szadaj]

Out of curiosity why are you NOT using yhe PCV system?

The very first time I started the engine, since I bought the car, and had the engine rebuilt, was Monday. If you look, I don't have the distributor advance hose attached either. I just wanted to get it started. I fully intend to hook up the PVC valve. Thanks just the same for noticing and warning me of the downside.

BTW.....the carb appears to be an original CARTER AVS.

Good eye. It is a 4640s, which is actually for a 1969 440 HP automatic. I should be running a 4428s, but they are rare and expensive.