Choosing an EFI throttle body to replace a Walbro carburetor requires more than matching a nominal diameter. Mounting-hole spacing, the intake passage, throttle actuation and installation clearance all matter.
Choke bore, venturi and throttle bore are different measurements
A carburetor passage can have different diameters at the inlet, venturi and throttle butterfly. The venturi is the narrowed section used in fuel metering; it should not be confused with the throttle bore or the diameter of the engine’s intake interface.
An EFI conversion uses an injector to meter fuel, but that does not by itself guarantee higher engine output. The result depends on the complete intake, engine and calibration.
Check the mounting pattern on the actual hardware
The original article recorded different Walbro mounting arrangements, including 31 mm and 46 mm spacing. These are reference observations, not a rule covering every series and revision. Confirm the part number and measure the carburetor and engine being converted.
Historical carburetor dimension table
The table preserves the original collected measurements in millimetres. It is not a newly validated manufacturer catalogue. Blank or ambiguous cells require confirmation, and repeated part numbers should be checked against the actual component.
| WT WTA WA | |||
| Choke Bore | Venturi | Throttle Bore | Carburetors |
| 19,05 | 6,35/7,14 | 11,1 | WT 366-1, WT 456-1 |
| 19,05 | 7,94 | 14,29/12,7 | WT 35-1, WT 38-1, WT 204-1, WT 357-1, WT 367-1, WT 381-1, WT 385-1, WT 417-1, WT 449-1, WT 450-1 |
| 19,05 | 9,53 | 14,29 | WT 35-1, WT 38-1, WT 204-1, WT 357-1, WT 367-1, WT 381-1, WT 385-1, WT 417-1, WT 449-1, WT 450-1 |
| 19,05 | 11,11 | 15,84 | WT 29-1, WT 356-1, WT 358-1, WT 464-1, WT 516-1, WT 517-1, WT 527-1, WT 613-1 |
| 19,05 | 12,7 | 15,84 | Wt 513-1, Wt 537-1 |
| 19,05 | 13,49 | 17,44 | Wt 171-1, Wt 172-1, Wt 228-1, Wt 285-1, WT 529-1, Wt 451-1, Wt 480-1, Wt 540-1, Wt 542-1, Wt 555-1, Wt 610-1 |
| HDA HD | Not recorded | Not recorded | Not recorded |
| Choke Bore | Venturi 0 | Throttle Bore | Not recorded |
| 17,44 | 11,11 | 15,84 | Not recorded |
| 17,44 | 12,7 | 17,44/15,84 | Not recorded |
| 19,01/17,44 | 13,49 | 17,44 | Not recorded |
| 19,01 | 15,08 | 19 | Not recorded |
| 19,01 | 15,08 | 19 | HDA-48B |
| 22,19 | 15,88 | 19,01 | HDA-77B |
| 22,19 | 16,77 | 20,56 | HDA-63 |
| WJ | Not recorded | Not recorded | Not recorded |
| Choke Bore | Venturi 0 | Throttle Bore | Not recorded |
| 22,19 | 14,29/15,08/ | 19,01 | Not recorded |
| 22,19 | 15,88 | 20,56 | Not recorded |
| 22,19 | 16,67 | 21,43 | Not recorded |
| 22,19 | 17,46 | 21,43 | WJ-64 |
| 23,38 | 18,26 | 21,43 | WJ-71 |
| 23,38 | 19,05 | 21,43 | Not recorded |
| WG | Not recorded | Not recorded | Not recorded |
| Choke Bore | Venturi 0 | Throttle Bore | Not recorded |
| 31,9 | 21,67 | 26,7 | Not recorded |
| 30,3 | 21,67 | 28,14 | Not recorded |
| 31,9 | 21,67 | 26,7 | Not recorded |
| 30,3 | 21,67 | 26,7 | Not recorded |
| WB | Not recorded | Not recorded | Not recorded |
| Choke Bore | Venturi 0 | Throttle Bore | Not recorded |
| 28,6 | 20,64 | 25,4 | Not recorded |
| 28,6 | 21,43 | 25,4 | Not recorded |
| 28,6 | 23,84 | 25,4 | Not recorded |
| 32 | 25,4 | 28 | WB-37 |
From a reference dimension to a working EFI configuration
Use the table to identify questions for the supplier, then confirm the engine-specific hardware, fuel supply, electrical requirements and calibration. Browse Löweheiser EFI systems and EFI engine options.
For references organised by engine model, see the small engine EFI conversion table.
Discuss your application
Send us your engine model, intended fuel, operating requirements and available installation details. Discuss your configuration with Löweheiser.
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