I need to know the best way to adjust my carburetor for power and maximum fuel usage.?

Question

I have a 4150 Series 600 CFM Holley carb monted on a 68 327 Chevy engine. It is running "Rich". Before I take it to an over priced shop what is the best way to tune the carburetor myself to obtain the best air/fuel ratio. I want power plus a better milage rate. As of now it is running so rich that it just drinks gas like crazy. Can anyone help me?

Answer 1

Sorry to Don E, but Ford Australia had smallblock 351 Cleveland V8s running 780 Holleys from the factory (road cars, not race) back in 1970 - most of the old big blocks out here in the USA were terribly under-carburetored.

There might be a problem with the carb you have currently. Sometimes the needle and seat in the float chamber wear out or get stuck, and the chamber fills to the top. This will result in running rich in a big way. I'd check this first.

If the carb is in good condition, what you probably need is to use different jets. A 600 Holley may be fine for some 327s, but it also depends on what other modifications you have done to the engine (a full-race motor could use an even bigger carb, while a luxury sedan couldn't even make use of the 600.)

Good luck!

Answer 2

If you are sure it is running rich, just change the jets. Remove the bowls and take out the metering block. Make sure you drain the bowls first, or put something under it to catch the gas. The jets will be screwed into the metering block. just take "THE RIGHT SIZE SCREWDRIVER" and remove them. The orifice size will be stamped on it. If your rich then go to a lower number jet. I would recommend maybe dropping it two or three sizes. If you drop it down two in the front, drop it down 2 in the back. The front jets and back jets may not be the same but drop them down the same amount. You can buy a whole set of jets for something like 40 bucks at any speed shop or a good parts dealer.
When you lean it out it will cause the engine to run a little warmer, So make sure it is running rich before you change them. Also make sure your gaskets are good before you reassemble. I would recommend replacing them.

Check your #1 and #7 spark plug to determine if it is lean or rich.

Answer 3

The 600 cfm Holley is designed for a 454 ci. engine.Put a smaller carb. on say a 450 cfm and it should not flood at low rpm`s.Talk to a racing Technician and he can tell you the right set up.

Answer 4

go talk to the local parts store dude and see if the guy has a "hot rod" buddy that understands your problem ...and maybe he can help you .... the true answer that you seek is not here on the net and you will probably make some new friends that have the same interests as you ... you need a hands on mechanic that knows what he is doing to help reduce the fuel consumption and get the most power from that sensitive carbuertor..........