This page [in the making] is the beginnings of the general principles of operation of the Walbro carb that is used on many engines in karting.

The Walbro carb we run in so many classes in karting is primarily designed for engines that run at two speeds: idle, and full throttle (full throttle meaning in this case; a stable, full load, high rpm). Think of a weed-eater or a chain-saw. These "devices" really only have to run at those two speeds. They must idle somewhat cleanly, and they must run somewhat consistently at a steady high RPM, under fairly consistent loads.

This carb we run in karting is an excellent carb for the above described applications. It is, unfortunately, very poor at metering fuel through a varying RPM and load range.

There are many theories as to how to make this carb function correctly for a given application in karting. Let me say right here and now: If your setup is working for you, do NOT start making major changes in your carb setup because of something I write here. On this page, (and subsequent pages), I will attempt to try and explain how this carb functions, and what effect changing pop-off pressure, arm height, and jet settings has on fuel metering through the load and RPM range.

Though I have fairly extensive experience with this carb (since 1977), nobody.... including myself, can say to you: "This is what you need to do" .... simply because there are far too many variables in karting. Any changes in gearing, pipe type and/or length, clutch slip, weight of kart and/or driver, track layout, driving style....etc. etc. ..... can, and DO, change what is required for correct fuel metering. There is no such thing as a carb that functions perfectly ..... every setup has compromises, and the Walbro carb is one of the biggest compromises in karting.

Tidbits:

Pumpers are available in two types of material: The "stock" (OEM-type) pumper is a black, flimsy-looking material. There is also an aftermarket "phenolic" pumper avialable. This pumper is a tan color, and appears as if it has a slight "weave" to the material. This pumper is slick feeling, and is quite a bit stiffer than the stock, OEM "black" pumper. The general consensus is that the black pumper might pump a bit better, but does not have the lifespan of the tan pumper.

The circuit plate flapper is also available in both materials (like the pumper). I have personally found no difference between those two.

The pumper gasket can usually be found in different thicknesses. I have generally run the stock (OEM part) gasket. There is an aftermarket gasket that is probably about twice as thick. I've found no benefit or problem with running that gasket..... though I prefer the "thinner" (stock) gasket.

More information will be added to this page.