OK, I suck at carb tuning so............

[Roothawg]

After reading several posts about the carb tuning gauges etc. I was wwondering if there is a general rule of thumb for you carb kings to adjust your carb?

Do you use a vacuum gauge and stop tweaking when it maxes out?
I have seen those emmission/tailpipe testers that Summit and Jeg's sell that are supposed to measure mixture at the tailpipe. Do they work?

[286merc]

How many carbs and which ones?

Usually a vacuum gauge is fine for a single 2 bbl or basic 4bbl.
The other tools become important with multi carb balancing issues but you still need a vacuum gauge for starters to get things in the ballpark.

[colorado51]

Generally, a good rule of thumb is to screw the mixture screws all the way in, and then back them out 2 – 2-1/2 turns. This is usually a good starting point.

[wingnutz]

Root

What do you have...? Single, double, quad, six, or eight carbs? Do you have a common plenum or individual runners?

If you're dealing with a multi-carb set-up be sure to have a starting refference point.

That means take all the adjustments to the neutral position..., in other words have all of the throttle plates in the closed position at an idle. Then place the meter over the carbs and adjust plates for the idle circuit until they ALL read the same. Set the idle mixture screws at 3/4-1.5 turns (single carbs at 2-2.5 turns) http://www.jalopyjournal.com/ubbthreads/images/graemlins/shocked.gif

You don't want the linkage binding anywhere..., or it will cause trouble tuning later on.

Depending on the type of linkage you have will determine how you should set the throttle plates at partial throttle operation..., it is at this point where you place the meter over the carbs and adjust until they ALL read the same at partial throttle.

You should be able to set all of the stops with the linkage adjustment screws to hold that setting.

Next I'd look into a mixture verification tool such as a "Gunsons Colour Tune" ..., it screws into the spark plug hole and has a glass optical that will indicate if you're running rich or lean depending on the colour of the flame in the chamber! You change the colour by adjusting the idle mixture screw. (This works great unless you're color blind...! http://www.jalopyjournal.com/ubbthreads/images/graemlins/tongue.gif)

There has been other posts explaining the meter as well as the Gunsons Colour Tune. PM me of what you have and or need..., hope this helps! http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

Mark

[four-thirteen]

I'm lazy as all hell, but I just put the stock jets in them, and back out the idle mixture screws to 1-1/2 turns. Screw in the idle adjustment until it idles nicely and doesn't kill. Use the same thing for 2, 3, 4, 6 and 8 carb setups.

On multi carb setups, balancing them all out is a load of crap (unless you have individual runners with no balance). Out of curiosity I pulled the linkage off one of the carter 4bbls on my plymouth to make a pass on one carb instead of both. It went about the same. Dave

[Unkl Ian]

A couple good links in the thread HAMB (http://www.jalopyjournal.com/ubbthreads/showflat.php?Cat=&Board=UBB1&Number=203164&page=0& view=collapsed&sb=5&o=14&fpart=1)

[Roothawg]

I suppose I would have to say that most of mine have single 4 barrels. Although the 235 I built has 2x1 Offy intake on it.

[wingnutz]

That has the common plenim and will be much simpler to work with than IR (Individual Runner) set-ups.

You don't even need the Colour tune with this set-up. But a Colour Tune might help balance fuel flow from the front cylinders to the back cylinders a little better. http://www.jalopyjournal.com/ubbthreads/images/graemlins/smirk.gif

Mark

[burger]

Root-

I use a vacuum gauge for everything. Worth every bit of the $20 you'll spend.

Before doing any carb tuning, I make sure that the ignition is set correctly. This is a black art in itself. First, I disconnect and plug the vacuum advance and time the distributor. On my SBF I like 10°. Next, I reconnect the vacuum line and since I'm using an adjustable vacuum advance canister, I play with that until my vacuum reads highest at idle. My adjustable vacuum kit came with new distributor springs and weights. No science there -- I just read through the instructions and selected the set that matched my engine.

Once all that's dialed in, I turn the mixture screws all the way in and back them out exactly 2-1/2 turns. From there, I tweak them both the same amount until I get the highest vacuum reading. There's usually a 1 - 1-1/2 turn range where I get the same reading, so I put it in the middle of that range. Next I adjust the idle screw until things sound right (I don't have a tach) and then repeat the mixture procedure.

Done.

My car and truck both seem to run very well and the spark plugs are the appropriate shade of light brown. My truck actually has some sort of new-fangled duraspark? distributor, so I just time it and let it go at that.

I'd appreciate any feedback or comments anyone has to offer on my technique. It's something that I came up with a year ago after asking Root's exact question on this board.




Ed