Walbro carburetors and equivalent Loweheiser throttle body

Small two-stroke engines usually come with Walbro carburetors, Löweheiser injection bodies have the same pattern as walbro carburetors to be bolt on.

Not all walbro carburetors have the same bolt pattern, small series have 31 mm bolt spacing and larger WG and WB series have 46 mm.

The carburetor size is not constant throughout the entire duct, it has a total of 3 different diameters, firstly the bore choke, it is the diameter of the inlet where the choke valve is. Then there is the narrowing of the venturi, the venturi has the smallest diameter because it is the point where the air accelerates to make the Bernoulli effect and draw in the fuel. This is the most representative diameter because it is a diameter that limits the passage of air when the carburetor is fully open.

However, the throttle body that replaces the carb does not take this value as a reference, but rather takes the last value, the throttle bore, which is where the butterfly is on the walbro carb, this diameter is slightly higher than the venturi.

This is the reason why the injection achieves a slightly higher power value than the carburetor. Electronic injection does not need the speed of the fluid to supply the gasoline as in the case of a carburetor. it does not need the narrowing of the venturi and therefore simply the venturi is eliminated, this makes the duct much cleaner and less restricted.

Then I have made a table with all the data that I could find. There is not much information about the diameters of the Walbro venturis, so I am going to make a collaborative table, if you know of any carb that is not in this table, please tell me.

(all diameters are mm.)

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
Choke Bore	Venturi 0	Throttle Bore
17,44	11,11	15,84
17,44	12,7	17,44/15,84
19,01/17,44	13,49	17,44
19,01	15,08	19
19,01	15,08	19	HDA-48B
22,19	15,88	19,01	HDA-77B
22,19	16,77	20,56	HDA-63

 

WJ
Choke Bore	Venturi 0	Throttle Bore
22,19	14,29/15,08/	19,01
22,19	15,88	20,56
22,19	16,67	21,43
22,19	17,46	21,43	WJ-64
23,38	18,26	21,43	WJ-71
23,38	19,05	21,43

 

WG
Choke Bore	Venturi 0	Throttle Bore
31,9	21,67	26,7
30,3	21,67	28,14
31,9	21,67	26,7
30,3	21,67	26,7

 

WB
Choke Bore	Venturi 0	Throttle Bore
28,6	20,64	25,4
28,6	21,43	25,4
28,6	23,84	25,4
32	25,4	28	WB-37