Hot Rod Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
194 Posts
Discussion Starter · #1 ·
I currently have FITECH efi system on my 65 Mustang. It works ok, but I want to return it to a carburetor. My question is - Can I still use the high pressure in-tank pump and a return style regulator to reduce the pressure to 5 psi for the carb without creating other problems? Thanks.
 

·
Registered
Joined
·
204 Posts
When using a regulator going from a very high pressure to a very low pressure (65 to 6 psi), the regulator is working in a very narrow range of its stroke at the shut off range when idling or cruising. This can cause erratic pressure variations.

At very low flows the regulator will be almost closed and as the throttle is opened the float in the carb will drop and cause a fuel flow increase but a large quick pressure drop which will cause the regulator to open from almost closed to a more open position. Because the regulator is not operating in its best stroke position (mid range) it will have a hard time maintaining a fixed pressure out and will be hunting (very small movement with large output variations). This would require a two stage regulator which I question the holley regulator is.

The way around this is to use two regulators in series, one regulator set to say 65 to 12 and the second from 12 to 5. The choice of regulators would be determined by the best operation range for each regulator so they are working in their mid range of their strokes.

Is this easier to do than installing the correct pump in the tank? If it was me I would install the correct pump. However, I would not rely on the pump to supply the exact pressure that is claimed by the manufacturer.

We as hotrodders have learned, mostly the hard way, do it right the first time and be done with it. To me the right way is to install a low pressure pump say 11-12 psi and install a return pressure regulator the get the best carb inlet pressure required. This way it can easily be adjusted up or down for fine tuning.

The exception to this is a mechanical pump run off the engine. EFI has make electric pumps a requirement and we have use them going back to carbs.

Also in doing this, do not pick a pump that has more capacity then required, more is not better. This can be just as bad as the regulator will be bypassing a larger amount of flow than is required and will be operating at almost wide opened during idling and cruising and the opposite of the above takes place.

Matching components for fuel is just as important to matching cam, head. intake and compressing ratio for an efficient engine.
 

·
Registered
Joined
·
210 Posts
I wouldn't do it. Swap back to the mechanical fuel pump and run a 3/8" supply line from the tank to the fuel pump then run a 1/4" line from the fuel pumps supply to the carb. I would run a Tee there or even better use a fuel filter for a 1964 Pontiac 389 with AC. Make sure you get the filter for AC. It will have the extra port for the return line.. Todays fuel requires a return line...

Welcome back to the sane side of the tracks.. I see people complicate there cars with all this modern stuff, might as well just go buy a new Mustang..
 

·
Old(s) Fart
Joined
·
6,016 Posts
They specifically make bypass regulators to allow you to run a carb from an EFI high pressure pump. No, you can't do it with a cheap AdvanceZoneBoys regulator. You CAN do it with the proper parts.
 
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top