Hey EPR i see that you don't run a choke with the 603 carb. What is the reason for that? When i open up my choke all the way my bike boggs out could that be because i am running 91 octane fuel on it? Is 100 octane racing fuel a bad idea for one of there engines?
You gotta learn how to tune..............The fastest and easiest way I learned was getting into nitro r/c from when I was younger til now...If you can tune-in an r/c nitro engine you can tune almost anything....
Walbro carburetors are almost standard on most all two-cycle engines. Adjustment of the carburetor may have to be performed on a periodic basis and most definitely after the simple device is rebuilt. Adjustment will not take long and the small screws may have to be "tweaked" after the engine has warmed up and been running for a few minutes
1 Identify the two-fuel adjustment screws on the side of the metal carburetor. One screw is labeled "lo" and the other is marked "hi". The "lo" fuel screw is for when the engine is idling. The "hi" fuel adjustment screw regulates the fuel when the engine is at full throttle.
2 Turn both of the screws, gently, in a clockwise direction to seat the base of the screw inside the carburetor. Do not tighten the screws with any form of a forceful nature. When dealing with these small carburetors "finesse" is a key word for beng really-really gentle but accurate.
3 Open the fuel adjustment screws in a counterclockwise direction one and three-quarter turns to two full turns. This is the starting point for all Walbro fuel screw adjustments.
4 Start the two-cycle engine. Allow the engine to warm up for approximately one minute to two minutes. The engine may be running a little rough, that is normal until final adjustments are made.
5 Hold the throttle wide open for full engine acceleration. Adjust the "hi" screw until the engine smooths out. In other words, the engine should not be missing or have any hesitation. In most cases the "hi" fuel screw will not have to be turned more than a one-quarter turn in either direction.
6 Allow the engine to return to an idle operation by releasing the throttle. At idle the engine should be running smoothly. Quickly depress the throttle again. If the engine hesitates open the "lo" fuel screw to a quarter turn counterclockwise. Perform the release and depression of the throttle a few times. The engine should go from idle to full RPM in a smooth progression. If the engine pops heavily at idle, when coming down from a full throttle, the "lo" fuel screw is delivering too much fuel. Turn the "lo" screw in a clockwise direction using no more than quarter turn increments.
On some of my 603 carbs I remove the choke from the carb and put the v-stack w/built-in choke installed in its place....You have to JB Weld the holes in the carb closed too.....The 813 carbs dont have chokes at all so a v-stack w/built-in choke will always be needed......