This kit for the Keihin CV-40 Carbs found on Harley-Davidson is an amazing invention. If you want more performance, this is a great addition. YOST POWER TUBE BENEFITS: 1. Produces a very fine mist The Yost Power Tubes by design, produce a very fine mist, finer than most production fuel injection systems and can be seen and observed by removing the air cleaner and looking into the carburetor venturi. 2. Mid-Range Power and Horsepower One of the Yost Power Tubes greatest benefits is extremely good PART THROTTLE response and MID-RANGE performance. This is the most affordable horsepower gain that money can buy. Typically, there will be an increase of 2-5 horses. 3. Increased Combustion Efficiency The Yost Power Tube provides increased combustion efficiency for a more complete burning of the fuel mixture so that you need less fuel to do the same job. The Yost Power Tube is specifically designed to synchronize the engine demand with the air and fuel requirements. (In other words, this Yost Power Tube gives you the proper amount of fuel at just the right time.) 4. Smoother Running Engine You will have a smoother running engine through the entire range, due in large part to the increased combustion efficiency. There is a greatly reduced possibility of pockets of raw fuel burning randomly. 5. Detonation In your combustion chambers, and again because of greater combustion efficiency, the possibility of detonation is also reduced. We have never ridden in scientifically or atmospherically ideal conditions, so I would still be somewhat conservative with compression ratios and ignition timing. 6. Reduced Possibility of Part Throttle Lean Spot This means that ideally you can use a larger carburetor, bigger ports, and more aggressive camshafts with a reduce possibility of a part throttle lean condition. (smaller fuel particles are easier to move and lift than larger particles) but use some wisdom and remember that if you set up a street engine to DRAG specifications, you may have drivability problems at lower engine speeds. 7. Shorter Warm-up & Reduced Spark Plug Fouling Most riders also experience shorter warm-up times and a reduced possibility of spark plug fouling. With increased efficiency, the additives present in gasoline are more completely burned, so much so that it is difficult to leave residue deposit on the spark plugs. 8. Jetting For Atmospheric Conditions Providing that your jetting is fairly close to the atmospheric conditions that you are riding in, your engine will run cooler. This can be checked with a thermometer in your oil bag. 9. Surges & Flat Spots The Yost Power Tube is designed to almost completely eliminate surges and flat spots by controlling air-fuel mixtures more precisely, and provides an almost unbelievably smooth throttle response and carburetor circuit transition. 10. Easier To Start The Main Fuel Circuit With the Yost Power Tube installed, it is much easier to start the main fuel circuit, while needing less manifold vacuum to do so.