Buckshot Racing #77 is now offering new 2.5 Drag ECUs built by CDI Electronics for the legacy Mercury Racing motors, where original boxes are getting harder to find, harder to trust, and harder to support.
 
This ECU is intended for the 2-stroke Mercury Racing 2.5 Liter Drag 300 and S3000, and it also supports modified Mercury 260 EFI and 280 ROS engines that are set up for this proven Mercury Racing ECU calibration.
 
Instead of forcing owners into random substitutes, this CDI-built ECU provides a direct replacement path for multiple Mercury Racing ECU families that share the same basic fuel pressure requirement and drag-style control strategy.
 
What this ECU replaces and supersedes
This ECU is built to cover two well-known Mercury Racing ECUs”= that racers and builders search for by box label and PROM ID.
 
The first is the drag-style box most people reference as Mercury Racing 9849A6 with PROM ID 7119. That combination is commonly associated with drag applications and a 56 PSI fuel pressure regulator, and it’s known for running an 11,500 RPM limiter.
 
The second family includes the legacy Mercury Racing boxes labeled A63, A47, and A7, commonly tied to PROM ID 7108. These also run with a 56 PSI regulator, but have lower 9,350 RPM or 9,650 RPM limiter settings depending on the specific race series.
 
If your current ECU label matches 9849A6 / 7119 or A63 / A47 / A7 / 7108, this CDI-built unit is in the correct replacement category.
 
Fuel pressure requirement: 56 PSI 
This ECU is designed around a 56 PSI fuel pressure regulator. On Mercury Racing EFI two-strokes, fuel pressure directly affects delivered fuel. Running significantly higher or lower pressure than the calibration expects can shift air/fuel ratios and reduce the safety margin that keeps a high-RPM 2.5 alive. For best results, use a quality regulator, verify 56 PSI at idle, and confirm pressure stays stable under load when the boat is actually accelerating.
 
RPM limiter behavior and why it matters
The drag-style 9849 A6 / PROM 7119 setup is commonly associated with an 11,500 RPM limiter, matching true drag use where the engine accelerates hard and lives at high RPM for short bursts.
 
The A63 / A47 / A7 family with PROM 7108 is most often seen with 9,350 RPM and 9,650 RPM limiter variants, which are common in many performance builds and certain racing combinations.
 
Your safe RPM still depends on the full engine and boat setup—porting, rotating assembly, reeds, fuel quality, timing, load, and tuning. A limiter is protection, not a recommended operating target.
Intended engine platforms
 
This ECU is designed around the Mercury Racing 2.5L performance and drag ecosystem most builders know by name. That includes the Mercury Racing 2.5 Liter Drag 300 and Mercury Racing S3000, along with modified Mercury 260 EFI and 280 ROS engines that are configured to run this style of calibration and fuel pressure.
 
If you’re adapting a modified 260/280, the critical step is matching your injectors and fuel system to what the box is designed to run, and confirming fuel pressure is truly stable at 56 PSI under real load.
 
A few checks that prevent headaches after installation
A replacement ECU can’t compensate for a weak fuel supply or poor electrical health. Before you bolt anything down, confirm battery voltage is strong, grounds are clean, and the fuel system can maintain 56 PSI when the boat is on the pipe. It’s also smart to verify injector condition and consistency—on these engines, cylinder-to-cylinder fueling balance matters as much as total fuel delivery.
 
Contact mike@buckshotracing77.com or +1-714-697-1716 with any questions.