Tuning

[naa10104]

Hello,

Need some guidance concerning tuning carb and initial timing using a vacumn gauge. Am told that this is the most accurate way to do this. Have a 73 351 C 2V auto. It is running pretty well just want to get it as close as possible. Is it correct that the timing should be adjusted first and then the carb ? My understanding is that the car must be at operating temp, disconnect vacumn advance from dist. and plug. Attach vacumn gauge as close to the carb as possible to a manifold vacumn source. Adjust timing to attain the highest/steady vacumn reading. If any issues driving, pinging, running on back the vacumn reading down a little and retest.

As far as the carb goes install vacumn gauge as above and set both mixture screws 1.5 turns out from lightly seated. Then do you close or open each mixture screw to attain the highest/smoothest vacumn reading. Once you get one side right do the other. Does this sound correct ? And again curious about whether you close(lean) or open(rich) the mixture screws when you first start adjusting. Then after mixture is right adjust idle to proper rpm. Any other info would be greatly appreciated. Thanks

 

[Bill73Ragtop]

You are on the right track for the carb tuning, but I've found the use of a variable timing light is the way to go to initially set the timing (with vacuum advance disconnected) for initial and total timing. Then you drive the car to check the engine 'under load' to see if it pings. If there is ping, lower the the timing until it disappears. This can be done roadside by loosening and turning the distributor in very small increments.

Many of my clevelands have run well with 14 deg initial and 36 deg total for smooth running. The next step could involve re-curving the distributor. There's a lot of good discussion on the forum on curving the distributor for even better operation.

 

[Don C]

I also prefer a timing light.

As far as which way to turn the screws on the carburetor, it could be in either direction. It will be obvious if you go in the wrong direction. I use a tachometer at the same time, for both timing and carburetor adjustments.

 

[c9zx]

When you adjust the mixture screws the idle speed may increase to something higher than you want. Reset the idle speed to the desired RPM between rounds of mixture screw adjustments. It will likely take several rounds of adjustments to get it where you want it. Depending on what air cleaner is used you may see a small change in idle when the air cleaner is installed.

Chuck

 

[naa10104]

When you adjust the mixture screws the idle speed may increase to something higher than you want. Reset the idle speed to the desired RPM between rounds of mixture screw adjustments. It will likely take several rounds of adjustments to get it where you want it. Depending on what air cleaner is used you may see a small change in idle when the air cleaner is installed.

Chuck

I made all the adjustments and the car runs well, only issue is a minor miss/hesitation at low rpm usually from a stop. I noticed when I was adjusting the mixture the same sort of issue was there and seemed to improve when I made the mixture richer .... mixture screws are out app. 2.5 turns from seated. Is it possible that they are still too lean ? Sometimes as I increase the idle to app. 1500 rpm at the carb in park I get the same sort of miss. Any suggestions ? I have the Pertronix ignition with a good coil and wires. I think it is fuel related. Thanks

 

[vozaday]

Aftermarket carburetor or stock? If aftermarket have you tried changing out your vacuum spring, squirter? I had a hesitation from stop with my holley carb and after trying a couple different combinations it solved the issues.

 

[Don C]

How old is the carburetor and how long since its been gone through? It's possible it's got something plugged up or needs replacing. What kind of carburetor is it? If it's Ford or Holley the power valve may have failed.

 

[naa10104]

How old is the carburetor and how long since its been gone through? It's possible it's got something plugged up or needs replacing. What kind of carburetor is it? If it's Ford or Holley the power valve may have failed.

Hello,

Should have mentioned that it is a Motorcraft 2100 2V original that was professionally rebuilt about a month ago. All parts replaced and flow tested ... it is mounted on the original stock manifold and connected to all the original hoses, vacumn line etc.