This month, Carl covers how to properly set the float height in your carburetor. Getting this adjustment right can solve frustrating stalling issues and prevent fuel overflow problems that plague many adventure bikes.
Most riders don't realize how important proper float adjustment is until they start experiencing problems. If your bike stalls every time you come to a stop at a traffic light, especially when you grab a handful of front brake, you likely have a float height issue. The sudden forward motion shifts fuel to the front of the carburetor bowl, causing the engine to stumble and stall out. On the flip side, if your floats are set too low, you'll have constant fuel overflow. You'll notice gas dripping from the overflow tubes while riding, creating a mess and wasting fuel.
The adjustment process works similarly across different carburetor types, whether you're working on the stock BST-40 that you'll find on the DR650, or one of our aftermarket Mikuni TM40s. Start by removing the float bowl with the proper JIS screwdriver, then examine the float assembly inside.
The key is understanding how the system works: as fuel enters the bowl, the floats rise and contact a needle valve that shuts off fuel flow. To check your setting, hold the carburetor upright and slowly tilt it until the floats just make contact with the needle valve. Measure the distance from the carburetor body base to the top of the floats at this contact point. Check your factory service manual for exact specifications, but the TM40 should generally be set at 19mm +/- 2mm and BST-40 should generally be set at 14.7mm.
If adjustment is needed, you'll need to remove the float assembly and bend the small metal tang up or down. Bending it up makes the floats sit lower, while bending it down raises them. After adjustment, reassemble and recheck your measurement.
Sometimes even perfect float adjustment won't stop fuel seepage. This usually indicates a worn O-ring around the needle valve seat that needs replacement. You can find it as part of a carburetor rebuild kit.
Taking the time to get your floats adjusted correctly will pay dividends in reliable performance and trouble-free riding. This simple maintenance can eliminate stalling during city riding and prevent messy overflow problems on your adventures.
Be sure to check out our video for more details.
As always, if you have questions, don't hesitate to e-mail, call, or text us!