Setting Carburetor Float Level.

On some motorcycles, the "float level" (an adjustment of the amount of gasoline held in the float bowl of the carburetor) is an important contributor to how the motorcycle runs.

On the XR400, for example, If you're tuning for max fuel mileage, the accepted level is 14mm.

Anal mechanics beware - this method is presented for trailhead mechanics, with tools carried on the trail. Also, there are some steps missing. We're assuming that you know how to raise and lower the float level (ie bending the float arm tab). All that is presented here is a trailside method to set it at a measured level (ie 14mm).

Here, the stock screws have been replaced by allen screws for easy maintenance on the trail.

Many folks question why carburetors are not provided from the factory with allen head screws. The reason is that Phillips head screws provide a natural 'torque limitation' to protect the carburetor body. The design of the phillips head screw makes it difficult for the novice mechanic to overtighten the screw. If allen screws were provided by Honda, instead of stripped heads, there would be a lot of stripped threads, which are much more costly to fix.

Recommendation: When using allen screws, yank on the short end of the hex wrench when tightening the screws. This leverage approximates the leverage of a screwdriver, and may prevent "Bubba" from overtightening the screw and either stripping the thread, or distorting the foat bowl. Overtightening will bend the corners of the bowl, and then the carb leaks.

Gas off, float boal removed.

A Side issue: Some folks think that the float downward travel needs to be limited but that just doesn't make sense. If this really truly increases performance, please email me and explain how the float can possibly sink on g-outs. The webmaster thinks that the physics of floatation renders such an argument illogical. Or if you don't care about the physics, but know for a fact that it really helps then email me also.

Press up on the float then turn on the gas and slowly lower the float. Determine the exact point where the gas drip starts to build before it starts to run out. This is your float level. Measure this distance with a 14mm wrench as shown. Bend the float tang (adjust) until it's 14mm as shown from the carb separation to the bottom of the float.

This plastic part.....

.....is easy to install when the carb is in your hand, with the floats facing upward. It's very hard to install when the carb is on-bike.
Also, it can be placed on the main jet boss in several different orientations, but only one is correct (correct as shown).

Create a tiny wire spring as shown to hold the splash cover in place against gravity.

I cut this one shown (on the trail!!) from the wire retainer spring from the fuel line.

Back to Trail Tips
See CycoActive Motorcycle Products or CycoActive GPS page.