Power Tuning - Carburetors
Make sure that you've got the ignition timing set correctly before you start trying to adjust the carbs and that the throttle is opening the carbs 100%. If using an air filter make sure you have a clean air filter element, and check the amount of pleats your air cleaner has. The more pleats it has, the less it will flow.
In a gasoline powered engine, engine vacuum is your measuring stick for engine performance and efficiency. Vacuum gauges have been used to improve performance by those tuners who know how to use them. The rule is, the more vacuum your engine is pulling, the better. The goal of adjusting the idle fuel mixture is to achieve the highest possible idle vacuum reading you can obtain at a set idle speed.
The more accurate the gauge, the better your results will be. The manifold vacuum of GS / EFE engines is measured at the cylinder head intake ports. Don't measure the vacuum into just one intake port. You will need to check the vacuum signal of all the cylinders, in order to adjust each one of the four (4) carbs accurately.
On GS / EFE engines, the intake ports of the OEM cylinder heads have already been taped by SUZUKI. You can purchased commercial vacuum gauge adapters or make your own. On my EFE Race Bike I have constructed a metering block tool that I can isolate each individual cylinder in order to measure the vacuum. This device enables me to make any adjustments to the air-fuel mixture screws on my RS Mikuni Flatslide Carbs in a timely manner. The objective of the indivdual carb adjustment is to obtain the highest reading of vacuum for each cylinder at a set idle speed.
If you are using RS MIkuni Flatslide Carbs although it won't affect WOT (Wide Open Throttle) horsepower, a proper accelerator pump adjustment is important to avoid an off-the-line bog. If your motorcycle has an off-the-line bog, and the exhaust pipe outlet is "black in color", the mixture is too rich, so adjust the carb's accelerator pump to reduce the amount of fuel that the pump squirts. If your motorcycle bogs and the exhaust pipe outlet is "normal in color" the mixture is too lean, adjust the carb's accelerator pump to increase the amount of fuel that the pump squirts.