® Carburetor felt seals

In some circles it is fervently believed that engine performance issues can frequently be traced to vacuum leaks at the throttle shafts. Sounds logical. Too bad it just isn't so. In more than 46 years rebuilding carburetors, I have yet to encounter this. In each case in my experience where someone believed the seals to be the cause of an unwanted performance glitch, it was found that there was another, completely different issue. Whether bowl venting problems, incomplete cleaning, inadvisable use of aftermarket parts, ignition timing issues, or simply inexpert carburetor adjustment, these shortcomings are hundreds of times more often the problem.

The felt seal fallacy is bolstered on forums which promote another misconception, that of spraying any number of materials onto carburetors and noting whether the engine responds. This is a "hack" procedure, that is, one no professional tech would ever use. The correct test is the less air test. See my article, The 60/40 Rule.

Many Keihin carbs have seals that are so loose you would intuit they would have to affect performance. But guess what: they don't. The fact is, the felt seals on carburetor throttle and choke shafts are not perfect seals and are not designed to be. Think about it: can felt really seal? They are dust seals for the most part. Carburetors having these seals are engineered to work properly with a small air leak. You can attempt to tighten this up if you must, but it will be fruitless. It will not solve a performance issue. Determine and solve the real problem instead. I sell theses felt seals, in all four sizes, because folks want them. But they are not the "silver bullet" many want them to be.

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