Carb Slide functional check, how to.

[katat58]

I'm in the process of troubleshooting my carbs, bike won't rev over 3500 after carb over haul, see post frustration X 10, been at it now for a week. Today I came up with a unique idea of how to check if your carb piston valve (the slide) is binding and if the diaphragms are pulling vacuum. You must have the carbs removed from the bike and drained. Keep in mind the carb slide works with air rushing under it and then causing a low pressure area in the venturi which in turn is pulling a vacuum above the diaphragm via an air hole in the carb slide body. This in turn causes the diaphragm to draw up raising the jet needle. Now how do you simulate this effect with the carbs off the bike? I took a shop vac and just held the suction nozzle up to the carb barrel on the engine side of the carb. As the air was being drawn thru the carb I then rotated the throttle control and opened the throttle plates and in doing so simulated the vacuum effect of a running engine. You then just look into the intake side of the carb and watch the slide operate. If it doesn't go up then of course you have a bad diaphragm, an air leak around the top of the carb or a sticky slide. Mine all worked perfectly. Another idea I came up with to check for vacuum leaks around your air box, vacuum lines, carb connection boots, and carb bodies. With the bike idling take a can of starting fluid and spray it around all of the areas just mentioned. If the bike revs up all of a sudden then you've located a possible vacuum leak. Be sure to use the starting fluid with upper cylinder lubricant in it, don't want to do any internal damage to the engine. I've done all this today and the bike still stumbles and goes flat past 3500 rpms. I'm readjusting the valves tomorrow and continuing my search for the cure. Hope this helps some of ya.

[Black_peter]

Good tip! And doesn't violate B_P's law prohibiting the use of compressed air on carbs!