Has anyone changed their primary jets?

Hey All
While reading about the Holley 4160, it seemed like the car motorheads like it because it is customizable. It looks like there are different ways to tweak it including playing with the primary jets. I have .66 jets in now. What would going up or down a size do?
Tom

Going up makes it rich, down leans it out. One size either way probably wouldn't do a whole lot. It's a minimal change and one you probably wouldn't notice.

This is the simplified process.
When you start changing jets you have to pay attention to the air/fuel ratios. New wave motorheads will use an O2 sensor to read what the A/F ratio is but that isn't a viable option with a wet exhaust. At least not without a whole lotta work to plumb an O2 sensor bung into the exhaust manifolds before the wet exhaust.

Old school way is put a new set of plugs in, disconnect the secondaries so they can't open and run it wide open and shut it down by cutting the ignition and not the throttle. If you start getting detonation, you're too lean, shut it down immediately and put bigger jets in.
Pull the plugs and see what color the insulator is. Grey is bad (lean, starting to melt pieces of piston), white is good, tan is OK (rich, not as efficient but better then grey). Not really a scientific process and even experienced tuners can misread plugs this way but can get you in the ballpark.
Better yet is to cut the threaded portion of the plug back to so you can closely look at the base of the insulator to see how much of a soot ring you have. Measuring it will tell you if you can go lean or rich.
It's purely a trial and error method, time consuming and wastes lots of plugs but can effective if done properly and carefully.

If you really want to dial it in then you do the same thing with the secondaries opening to tune them. On a 4160 the secondary side is much more difficult to do because you would have to change out the whole metering plate. A whole nother discussion that I won't get into but you get the idea.

Generally, factory carbs are fat from the factory so going down a couple jets sizes usually won't hurt but pay attention to the plugs. It's always better to be too rich than too lean.

Tom was saying it doesn't have the punch out of the hole it used to have. Could be explained by a smaller power valve in the latest carburetor?

Hey Guys,
I just rebuilt this one and it has a new 6.5 PV in it. I am "satisfied" with the punch it has now, BUT it just seemed marginal. I guess I could check and see if the secondaries are kicking in at the right time.

Just the initial punch off the dock for a dock start.