Z  Tech Tips  Triple Mikuni Carbs 

Tony D Triple Mikuni Set Up Procedure 

1.   Disconnect the downlinks to each of the carburettors so the carburettor throttle bell cranks are resting against their IDLE stop screws. This is a greyish screw attached to a stamped sheet metal bracket on the right or the left side of EACH carburettor.
 

2.   CHECK FOR BENT THROTTLE SHAFTS. Put you meter on the front and the rear barrel of EACH carburettor. Find which one is the lowest reading, that is the one you need to do synch on
 

3.   PICK A BARREL on each carburettor. FRONT OR BACK. Doesn't matter which, do this with regard to the above test, so you have the throttles that are CLOSED THE MOST at idle. Usually this is cylinder 2, 4, 6 on the standard setup.
 

4.   Set the synch meter so the HIGHEST READING barrel of those three is in the middle of the meter's range by adjusting the screw (Unisynch) or by reading the number (Weber Tool). By using the above mentioned IDLE STOP SCREW, make each barrel flow the same by adjusting the screw in or out. Engine speed is irrelevant at this time.
 

5.   Once they are all in synch, then slowly turn each one back down or up to make idle speed (850-900rpms). Check on the same three barrels each time so you have them all flowing EQUALLY at that idle speed.
 

6.   Adjust the brass screws using a tachometer or mercury manometer for highest idle speed (Best Rich setting is preferred for performance, search the archives, I'm not going over that again)
 

7.   Readjust the idle speed with the IDLE STOP SCREWS again, and make sure they are flowing equally.
 

8.   Repeat as necessary until you have the highest idle vacuum and lowest throttle opening. You now have carburettors synched at idle, and adjusted for idle. Now to adjust off-idle.
 

9.   Turn the car off, no sense doing this and having it vibrate and be hot while your fingers are in there. Adjust EACH linkage, one at a time so they EACH attach to the bell crank on the throttle rod easily---they slip on and off the little pivot ball WITHOUT moving the other linkages. If you have one too short, that carburettor will be at idle speed and the others will be held open slightly at idle, and this will continues up the speed range. Once all the linkages are adjusted so they are opening evenly, and all slip on and off without disturbing any of the other carburettors, depress the throttle and make sure they all open the carburettors to 100% open, and at the same time. It is possible if one of the bell cranks on the throttle rod is far enough out to line with the others you could have one carb not opening all the way, but this is not usually the case.
 

10.  Restart the car, check your idle synch--it should not have moved. If it did, disconnect the throttle linkages, and see which one is too short holding the other two open and fix it. Once they are confirmed to be in idle synch, then open your throttles off-idle, and USING THE SAME BARRELS OF 2,4,6 and opening your uni-synch almost wide open, stick it over the barrels and see if they are all flowing the same off-idle. If so, you are done. The uni-synch SUCKS for this part of the test, and really for the first part of the test. I prefer the Weber tool with a direct reading number, but such is life.
You are now done. Use locktite green on all the linkages to lock them in place, and LEAVE THEM ALONE. This should NOT have to be anything done once done correctly and properly secured the first time.

Bent throttle shafts suck, and I don't recommend "bending them back" like Brian said, because I have never had one go back and not go too far. There was a time you could buy new shafts, but good luck with that now. If you synch them this way (by using the furthest closed barrel) you should be fine even with shafts that are slightly tweaked.

 

More Tony Tips:

It sounds difficult, but is pretty easy. If you had the carbs off the manifold, you can get REALLY close using a 0.002" feeler gauge and presetting all the idle stop screws that way, and then adjusting your linkages to match up as above---doing it that way really saves time, because in theory they will all be flowing the same with the same throttle opening unless you have a problem with an individual cylinder

 

Do a valve adjustment, general tune up and new plugs to make sure everything is up to snuff and they are all hitting strongly as they should before screwing with the carbs.

The above process is the same for triples, quads, duals. Same for VW, Porsche, BMW, Toyota, Nissan.....

Carbs is carbs... Piece 'o Cake.
 

Links:

http://www.gracieland.org/cars/techtalk/Mikunidata.html