Air Fuel Mixture???

[HOT-ROD]

WHAT ARE THE STANDARD SETTINGS FOR MY 39FCR??? HERE IS WHAT I AM RUNNING 40PILOT 170MAIN BUT I CANT FINE TUNE THE 2 AIR FUEL SCREWS . WHAT IS THE ONE IN THE BACK OF THE CARB FOR??? THE MOTOR IS BEEN REBUILT AND IT HAS DMC EXAUST.

[methyman]

Adjust the fuel screw (engine side) by first turning it out until you notice a decrease in idle speed, and then in until you notice a decrease in idle speed. Note the range between these two points. Find the spot in this range where you get the best off idle response when "slightly" wicking (opening) the throttle. If you end up more than 3 1/2 turns out go a size larger on the pilot, and if you go in less than 1 1/2 turns go a size smaller.

With the needle on the third groove, see how it runs from 1/4 to 3/4 throttle If it feels lean, lower the clip to the 4th position. If it runs too rich on the 4th position, go back to the 3rd position and now look at adjusting the accelerator pump so it pumps quicker. Since I've never had to adjust mine, the only help I can suggest is to call Sudco at 323-728-5407. They've always been helpful when I've called and can probably provide you with instructions/options on how to do this.

Lastly, once you get the 1/4 to 3/4 range dialed in, move to the main jet (3/4 to WOT). The best way I've found to dial in the main is to use a method I call "purposefully over-jetting". Start with a large size main and do a run with the throttle above 3/4 and the engine under load just under the rev limiter--you'll know if you're too rich when the engine blubbers similar to running with the choke on. Also, make sure you can distinguish the difference between the blubbering condition and hitting the rev limiter. Once you know you have too large of a main installed, do a high speed run just under the rev limiter and then do a plug chop by quickly killing the engine and pulling in the clutch at the same time. Coast to a stop, pull the plug, and check the porcelain for a light brown color. Keeping doing these runs and going down in main jet sizes until the blubbering condition goes away and the plug reads light brown--once you get to this point the main is perfect. Also, keep in mind that clean burning fuels will make it very difficult to get a good plug reading.

[HOT-ROD]

ITS A50 PILOT INSTEAD OF A 40,MY BAD