The Walbro WG-8 Carburetor
by Had Robinson & others www.SouthwestAirsports.com
If you want to save hours searching for info on the Internet and not learn the hard way, check the sites and info below. There are many pilots who understand how Walbro carburetors work, especially the WG-8, and I have posted their important work here. The Walbro is a simple device but it is not tolerant of abuse or improper calibration. This page is specifically for the WG-8 but most of it applies to other models, as well. Remember: The WG-8 has no way to easily modify the high speed mixture except by replacing the fixed jet. The jet is custom made for Miniplane and they do not offer different sizes, I am sorry to say. If you need to modify the jet size, see my tech note below. Do not consider making changes to the high speed mixture unless you install a CHT (cylinder head temperature) gauge. Failure to have a CHT could result in burning up your engine. The "spark plug color" method is imprecise and time consuming and I do not recommend using it. It is for general use only and is nearly useless for any accurate jet calibrations. If you have any questions or comments let me know.
If you do not want to do the repairs yourself but have a professional do it, I can help. Please contact us for details.
Calibration & Modifications for the WG-8 - by Gerry Farell This includes information on setting the metering lever height properly. Additional notes by Had Robinson. It is critical to the engine's performance under high loads that the metering lever be correctly adjusted.
Carburetor Adjustment - by Had Robinson -- How to adjust the low and high speed systems.
Modification - by
Richard Cobb -- An excellent tech note on the
problems with the Walbro carburetors (especially the metering lever) and how to fix them.
Additional notes by Had Robinson
Fuel System Test - Here is a quick and easy way to check whether your entire fuel system is functioning properly.
Jet Size Modification - by Had Robinson -- This tech note shows how to modify the existing jet in your carburetor without making permanent changes.
Parts Diagram -- This image can help you identify everything inside the WG-8. The model used by Miniplane has a FIXED main jet instead of an adjustable "power needle" and is only available from Miniplane. If you need other parts, like a rebuild kit, contact us.
Pop Off Spring Adjustment - by Mike Forbes -- The combined functions of the main jet and the pop off spring mostly determine the air/fuel ratio delivered to the engine. However, only the pop off spring pressure is easily changeable. The correct pop off pressure for the Top 80 is 1.2-1.3 Bar (17.5-19.0 psi).
Priming the Carburetor without Flooding the Engine - by Had Robinson
Service Manual - from Walbro -- This is not very helpful but has some information not available anywhere else.
Starting the Miniplane - by Had Robinson -- This can be helpful after storing it for a while.
Throttle Shaft Play - by Had Robinson -- Worn throttle shaft bushings will cause the carburetor to leak air and cause stalling or poor performance at idle and low speeds. Is your carburetor worn out?
This site was last updated 07/03/14