The Carburetor! for the lucky owners of the Mikuni Feedback Carburetor <img src="/forums/images/graemlins/pfft.gif" alt="" /> The first thing you need before you start your carb quest is the Factory Manual for your specific year. Otherwise you might as well beat yourself with a baseball bat in the dark. It's less painful and does not require as much brainpower. If that does not scare you then besides basic tools you will need a hand vacuum pump and a nice digital multimeter. I am by no means the expert on the carb. I learned most of this from other forum members and by RTFM ( reading the friggen manual )
The Major issues.
1. The Depression Chamber, it's a UFO shaped vacuum device that opens the 2nd barrel on the carb. When they go bad they don't hold vacuum. The 2nd barrel does not open resulting in a very sluggish performance.
To test, remove air cleaner, remove vac line to depression chamber and attach a vacuum hand pump. Open the primary barrel by either having a friend press the gas pedal or by hand on carb ( 2nd barrel will only open when first barrel is open ) Apply vacuum and watch for 2nd barrel to open. It should hold vacuum and not leak down. If it does not open or leaks down you need a new depression chamber. Test procedure in manual.
2. The Bowl Vent Valve. Your carb is heated by engine coolant. When you turn the engine off the gas in the bowl of the carb produces gas fumes. These fumes exit thru the bowl vent valve and collect in the canister next to the passenger side front head light. If the bowl vent valve is not working the fumes collect in the intake manifold and cause the engine to flood and hard start. The bowl vent valve does not come in a standard carb rebuild kit and there lies the problem. The Mukuni is a complex carb and needs fixed by someone with experience. DonÆt think you can crack open a Mikuni and slap a rebuild kit to fix all your problems.
3. The Sensors. The feedback carb is controled by the ECU via input from four sensors. Some carb problems are not really carb problems but sensors problems. You have to check the sensors first before you blame the carb. People want to tinker with the fuel-air mixture all the time but it ends up being the O2 sensor <img src="/forums/images/graemlins/smile.gif" alt="" />.
A. Engine Speed Sensor
B. Throttle Position Sensor, AKA TPS
C. Oxygen Sensor, AKA O2 sensor
D. Engine Cooland Temperature sensor.
4. The Maze of Vacuum lines. The vac lines are color coded and you just have to tag them when you remove them. The chart under the hood is OK but nothing is better than tagging them if you have to remove the carb. The vac lines like to crack on the underside where the attach to the nipples. You have to check each and every one for cracks, because a vacuum leak will cause problems. There are two major switches, the Thermo Switch and the Thermo Valve, there plastic and like to crack. The carb comes in a variety of configurations, Federal and California, Federal with High Altitude, California with High Altitude and all over again for either Manual or Automatic tranny. The manual has the test procedures.
5. The Choke. The choke is electric and controlled by the ECU. The test procedure is in the manual.
Do your homework before complaining on the board about your carb. Saying your carb is being strange does not give us much to work with. We need the whole story to give any type of reply that is helpful, or at least get you started in the right direction.
Thats all for now, I have to get back to my paying job.
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