Carbkie.html, Keihin FCR Carb Tuning Procedures Keihin FCR tuning manual Version 3.3 By Many thanks to Marc Salvisberg, founder of, for teaching me the finer points of using dynamometers and tuning carburetor equipped engines. I'm sure he still disagrees with some of what's here (my dislike of changing float level, and even suggesting that one use a lambda sensor, for examples.), but this version of my FCR tuning manual is a lot better than the ones I wrote before I did my stint as a technician at Factory. Carburetor Jetting & Tuning Page of Information. Jetting Keihin Slide Carburetors. The following is a guideline for jetting Keihin carburetors. Turning IDLE MIXTURE SCREW (CR, PWK, PJ, PE) controls the amount of air to the IDLE. However these might be for specific carburetors we highly suggest you read them. Keihin Cr Special Owners Manual Keihin CR Special Smoothbore Carburetor Owners Manual HERE. Keihin CR Honda CB250 CB 250 N Owners Maintenance Instruction Manual 1980 HERE. CRS General - CR Special Racing Carburetors. CRS carburetors are easy to tune because all jetting parts are available. About Keihin. Leadership; Philosophy. Thank you, Marc. After attending some AMA road races over the last few years as a dynamometer operator for Factory Pro Tuning and mechanic for, and having the opportunity to talk with lots of racers, I've learned to my absolute horror and amazement that you people are actually *using* the information on this page to tune your race bikes. God help you all. Someone asked me for info on using a Dynojet inertial dyno to tune a bike equipped with FCRs. Since I'm all too aware of the fact that most people don't have access to a proper brake dynamometer and an exhaust gas analyzer, I put together an. Before you do anything, MAKE SURE THE CARBS ARE CLEAN. Tear them completely apart (don't forget to remove the idle mixture screws), blast everything with carb cleaner, and blow out all passages and jets with compressed air. If you neglect this critical step, don't be surprised when, after fourteen jet changes, you find that a shred of fuel line or bits of rust from the gas tank (yes, even on YOUR bike, even with a fuel filter) had gotten lodged in some passage or another, causing the 'jetting' problem you were trying to solve. If you're running a ram-air setup, and the carbs don't sit inside the airbox, you'd better route the float bowl vents to the inside of the airbox or you'll never in a million years get the thing working properly. If the ram-air works at all, as soon as the bike gets rolling along faster than a walking pace the mixture will go dead lean. If you're running a ram-air setup, and using gravity feed rather than a pump to move the fuel from the tank to the carbs, you'd better route the fuel tank vent to the inside of the airbox or you'll wonder why it keeps sputtering at the end of long straights. 160 mph worth of air pressure in the float bowls and only ambient pressure in the tank will seriously slow down or even stop the fuel coming in from the tank, and the float bowls will run dry. You need to put airbox pressure into the tank to keep the fuel flow constant at various speeds. And I'm not kidding about the float valve seat sizes. Scroll down to the bottom of the page to get the scoop. I didn't come up with the chart. It's straight from Keihin. Keep in mind that you will spend much less time tuning the carburetion in following order: 1. Ultimate spider man video game pc download. Main fuel jet and main air jet (must be selected first since they feed the emulsion tube, which feeds the needle jet and jet needle). Root diameter b. Clip position (which includes the L1 measurement) 3. Slow fuel and air jets. Fuel screw 5. Accelerator pump (It helps to leave this disconnected during dyno testing so as not to create a momentary artificially rich condition which may lead to misleading exhaust gas analyzer readings. Keihin Carburetor TroubleshootingHowever, it's surprisingly time consuming to remove or install the pump connecting rod. If I had all the time in the world and were doing development work, I'd disconnect it. Racing Carburetor TuningIf I were at all in a rush, I'd leave it connected and just hold the test point a little longer to let the EGA get a solid reading.) You may find that if you change the taper of the needle a great amount, you may have to go back and reselect the main fuel and air jets since the tip of the needle can affect the full throttle mixture. Synchronizing: I've had pretty good luck synchronizing the carbs off the bike. Using the shank of a very small drill bit, adjust the idle speed screw until you can barely fit the base of the drill bit under one of the slides as you would a feeler gauge. You may have to remove the idle speed screw from the carbs and temporarily remove its locking spring to be able to thread the screw in far enough to slide a drill bit in unless you have some pretty small bits. Do this from the engine side of the slide as opposed to the intake side, and make sure the carbs are oriented such that the slides are moving vertically, so their weight takes up any slack in the throttle linkage.
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