MSD 2920 Atomic EFI Master Kit - Manual

Selecting a Return or Returnless Fuel System
The Atomic EFI has the option of working as either a return or returnless style fuel system. While many
users will have the option to choose whether or not to install a return line, there are a number of factors
that need to be considered in making this decision. NOTE: If you are planning to use metal tubing for
your fuel system, then a fuel system with a return to the tank is recommended. Using the chart below,
consider the conditions under which the vehicle with the Atomic EFI will be used on a regular basis.
For best results, always plan for the worst case scenario (in this case, the hottest daytime temperatures
where you will drive the vehicle using the lowest grade gasoline you will purchase). After taking all sec-
tions into consideration, at least five points should be accumulated to ensure reliable drivability with a
returnless style fuel system.
Condition Your Points Points
Daytime Temperatures
81˚F or greater  +0
71 - 80˚F  +2
61 – 70˚F  +3
60˚F or lower  +4
Quality of Fuel
Low (less than 89 octane)  +0
Medium (89 – 90 octane)  +1
High (91 octane or greater)  +2
Fuel Pump Installation
Greater than 2 feet from tank  +0
Less than 2 feet from tank  +2
In-tank  +5
A minimum of 5 points is recommended
to use a returnless fuel system
Total: _____________
The Atomic EFI with a returnless fuel system is NOT meant to be a solution to fuel vapor lock issues
that already exist on a carbureted engine. The Atomic EFI with a returnless fuel system is equally as
susceptible to vapor locking as a carbureted system would be. Therefore, if vapor lock has been an is-
sue on your vehicle in the past, it is not recommended to use a returnless fuel system with the Atomic
EFI. Instead, use a fuel regulator with a return line to correct the issue.
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© 2012 Autotronic Controls Corporation
FRM30904 Revised 09/12 Printed in U.S.A.