no vacuum on carb number 3

I have been at this for what seems like an eternity. I completely pulled my XJ650 Maxim apart over the winter. I painted the frame, fenders and tank and put it all back together after completely going through anything that could possible need replacing. I just installed brand new valve shims courtesy of chacal and installed them. I had some trouble with the valve cover gasket. I tore a small section and had a pretty crazy leak down the front of the motor. That's since been repaired. Here's where I'm at......I attempted to sync the carburetors. I got carbs 1 and 2 synced together just fine and dandy. I have absolutley no readings of vacuum on the number 3 intake! What the heck. I have good compression in the cylinder. The carbs were meticulously cleaned and new parts were installed as needed. I checked did a bench sync and checked float levels. Everything was done according to the XJ gods. I have absolutely no idea where to go from here. Please point me in the right direction. I had to put my tools down this morning and leave the garage before I turned green and my bulging muscles ripped through my clothes again!

 

did ya make sure the stub on the carb boots not plugged....kiss.

 

To quote Homer Simpson, "D'OH!"

 

TFD, what port are you using for the #3 carb? It is the vacuum port for the petcock. Are you using your tank to supply fuel, or an auxillary tank? If bike tank, unplug petcock vacuum line from carb boot, and connect vacuum line from gauge. When ready to fire the bike, petcock should be in prime position.

All the other carbs sync off of #3, and the sync screw for it is actually the idle screw. You may have the idle completely closed, which is going to close the butterfly valve and stop vacuum on the #3 carb. Try turning the idle screw clockwise in about a turn (raising the idle), and see if you get vacuum. If so, then you will have to redo your bench sync and give the running sync another go.

This is a suggestion from member Polock, and I have found it to be the best way (for me) to bench sync. Look into the carbs at the filter side, at the top of the carb throat, you will see 3 holes. When the butterflies are closed completely they obscure these holes and block vacuum which blocks the flow of fuel. For a good base bench sync, close the idle screw, then open it until half of the first tiny hole is showing. Then adjust sync screws on 1, 2, and 4 to get the same half of the first tiny hole showing. This will get you very close in the ballpark to do a running sync. Also remember to raise the idle a bit higher than normal, (I shoot for 1200rpm) and blip the throttle after very single screw adjustment, regardless of how minuscule. Good luck...