How-To: Remove Motorcycle Carburetor Welch Plug
The most important passage to clean during a carburetor rebuild may be hiding from you under a welch plug. The factory will install a hard to remove plug right above the fuel adjustment screw. I’m not sure of all the reasons why they install them, maybe to prevent people from tampering with the fuel/air mix due to EPA concerns.
Why Remove Them?
The fuel screw under the welch plug & the pilot jet meter fuel for the idle circuit. This is the first and most common passage to get gummed up, since it is the smallest orifice. Also, after the carbs are cleaned or rebuilt, you really need to adjust the fuel screw(s) to what your engine WANTS, not what the service manual calls for. The service manual may be a good starting point, however they are usually too lean (I’m talking about 4 stroke street motorcycles here). Better throttle response and performance can be achieved with proper pilot jet and fuel screw settings.
How-To: Tune Your Fuel Screws
Here is a video that explains fuel screw adjustment once your carbs are clean. See this post on pilot jet sizing.
Tools
I have no idea what brand my pick set is. In fact I have several sets and have “custom” bends in some of them.
Comments
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Great video! Companies put those “welch plugs” on the air/fuel adjusters for the sole purpose of emission regulations. They don’t want anyone to change the mixtures, but once you do remove them, it truly makes all the difference in tune-ability and dialing those carbs in properly! Great read! Keep up the great work!
Hi Cody, you have that exactly right. The fuel screw settings are also set really lean in most cases. If you hit 3 turns out on the fuel adjustment, consider bumping the pilot jet 1-2 larger than stock. That alone makes a huge difference in performance.
06 Honda shadow deluxe 600 ,some body before I had the bike strip the “D” shaped mixture screw and put in a normal screw in the spot. I’m asking if I was to take the screw out and some how get the rest of the mixture screw out could I save it and put in a new adjuster screw.
Email me some pics.
Of course the reason for the plug is emmission related. The EPA requires that all motorized vehicle models pass the applicable smog and fuel economy tests, and the OEM is responsible for making sure that the consumer can’t easily make changes that would cause the engine to run richer (increase smog emissions and fuel useage). It’s a given that the air/fuel mixtures on almost all vehicles aren’t ideal for performance as they’re set from the factory (my ’18 Passat clearly runs lean), so those engines will be happier and live longer if given the proper amount of fuel.
True that!