Vacuum ports on Mikuni?

[the_journeyman]

I've searched three different forums and can't find an answer.

 

I'm working on sync'ing or balance my triple Mikuni carbs. I've done this several times on motorcycles with just a vacuum gauge with great success. I know it's not a Unisyn or similar, but patience yields just as good results.

 

The vacuum advance for the dizzy is connected to #1 carb.

 

The middle carb doesn't have anything, and I can't get a vacuum reading on the port.

 

Third carb, can't get a reading.

 

I'm trying to connect to the same place the advance tube is connected to on the #1 carb, but I don't have the tall nipple like on the #1 carb.

 

What am I doing wrong?

 

Thanks!

 

JM

[Sam280Z]

The carbs do not have ports for balancing like motorcycle engines. I guess you could install ports in the manifold, but accepted practice is to use a flowmeter like a uni-syn or, better yet, a synchrometer. These measure airflow through the throat.

Sam

[beermanpete]

You might be able to drill and tap holes in the manifolds near the base gaskets. Install hose barbs and connect the gauges. If you use mecury columns be carefull; the larger displacement might pull enough vacuum to lift the mercury past the top of the column and into the engine. This would be most likely when closing the throttle from a higher engine speed.

[Tony D]

Mikuni Manifolds have ports for Mercury or Oil Synching of the airflow.

 

Otherwise, it's as stated above: Flowmeter is the only option out of the box if you don't have the Mikuni Manifold.

 

Can't use carb vacuum port for distributor advance for synch anyway!

Edited September 19, 2011 by Tony D

[the_journeyman]

Thanks for the input! I do have threaded ports in the manifold, but when I remove the hex nuts that are there, it's just metal underneath. It's like it's possible, but I'd have to drill underneath the nuts. Not something I'd want to do unless I had the manifold off the car so I could get all the shavings out. I'll just go with one of the other methods or the ear method. I got them close just going by RPM changes & smoothness. I'm not too impressed with whoever did the initial setup on these carbs. Each carb is running a 95 & 105 main rather than something matched & closer to 130.

 

JM

[the_journeyman]

I do have the Mikuni manifold, and on closer inspection with better light, it turns out I have some type of semi-soft plastic looking stuff sealing the port, not metal. It just looked metal on the one port I checked. It's soft enough to press the tip of a knife into with a bit of pressure. I'm assuming these were sealed to prevent a vacuum leak?

 

Here's a couple pics:

One pic shows overall, I have the allen screws out, but you can't really tell much about them.

 

Closer pic - turns out it's not solid, it's a white-ish sealant looking material, but very stiff. I can get the tip of a knife blade to dig in.

 

JM

[the_journeyman]

Update: drilled center of sealant out big enough for the tip of my vacuum gauge. Worked fine, no problems checking vacuum & syncing with the vacuum gauge.

 

Next issue:

 

Revival with more questions!!! While I'm working out some the fuel jets, I'm still tinkering.

 

Lean, Rich, Just Right (working on pilot circuit) 57.5 Pilots, 2.75 turns out starting, fresh plugs.

 

Carb #1 - snow white plugs (lean)

Carb #2 - Black, sooty (rich)

Carb #3 - Light brownish (about right)

 

I adjusted the idle (pilot) screw for each carb.

 

Carb 1 - 1/4 turn richer

Carb 2 - 1/4 turn leaner

Carb 3 - No change

 

Do I need to be looking somewhere else instead of monkeying with pilot screws? Should I check on float levels? I did check for intake & vacuum leaks with Ether and found none.

 

Thanks for the input!

 

JM