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post #6 of (permalink) Old 07-05-2009, 11:30 AM
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where is the hook up on the base plate?
i've got the stock intake manifold, and a mr. gasket adapter plate for the mc2100
If you need to tune the carb, just drill/tap the base plate adapter for base plate vacuum signal.

on the intake manifold, below the throttle linkage there is cube shaped brass fitting, it feeds vacuum to the brake booster. There is some serious vacuum coming out the other side of that fitting. I've had it capped off since i've owned the rig. Should i take the vacuum reading there?
This would be Intake Manifold 'Plenum' vacuum signal,
and it's almost as good as baseplate vacuum.
The 'Plenum' is simply the transition area in the manifold between carb throttle bores and the intake runners.

For determining if you have problems with valves and such, this is a good place to start.

If you want to know WHICH valve is causing problems,
Then you will have to tap into individual runners and sample vacuum as close to the cylinder head runners as you can.

With an 'Engine Miss',
You would be better off pulling the spark plug wires off the DISTRIBUTOR CAP one at a time to determine where the 'Miss' is...
(Before you go pulling plug wires off the cap, Strip about 5" of electrical wire, and make a circle out of it.
Ground the other end of that wire,
And then pull the coil wire, and lay that circle around the coil wire terminal on the top of your distributor cap.
this will give a reasonable ground to the spark energy while you are pulling spark plug wires)

Remember, an exhaust leak at the head will sound just like a 'Miss' to someone that isn't experienced with this!
Leaks should show up with a black soot trace where they are leaking,
And you can use a feather around exhaust gaskets,
Flanges where tubes connect to header plates,
And up and down tubes to find a pinhole leak that will make a 'Miss' sound when that tube is being used.

Also, an infrared heat gun (about $20 now, dirt cheap many places) aimed at each exhaust tube will tell you which tube is 'COLD'...
'Cold' tube is the 'Miss'!

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