Free Carburetor Manuals

Ignition & Ignition timing has a direct effect on carburetor tuning & operation, make sure that everything is straight before making final carburetor adjustments. This means ensuring there is a good hot spark at the plugs. A mechanic's vacuum gauge is extremely useful for engine diagnostics, carburetor tuning, and fuel pump testing. I would not attempt a tune-up without it. They are inexpensive. It's important that the power valve for example is correctly sized for the application & elevation. A modified engine with performance camshaft or operating at higher altitudes requires a correction factor, the stock power valve supplied with most carburetors and kits will not work correctly.

Carburetors are kind of interesting, it's possible a jet size change is needed with headers or dual exhaust though it's not a certainty. The only way to be sure is to measure the AFR. Increased velocity or scavenging may simply pull more fuel from the well depending on carburetor venturi size, making it a wash. Better breathing also means you can use a larger carburetor for better performance though this doesn't mean the jet size changes.

Make sure the distributor mechanical advance operates smoothly up and down the RPM range and reaches the specified advance. This is usually around 36° or so BTDC without vacuum advance connected. Make sure the vacuum advance diaphragm doesn't leak when it is connected, and the breaker plate moves smoothly.

What I'm getting at, other engine defects will make carburetor tuning difficult or impossible and the usual result is the mechanic tries to "tune around" the problem with the carburetor to compensate. The manuals are free to download and will cover far more than anybody wants to type out. A little time spent on setup and adjustment with attention to detail will be well rewarded.