The Stovebolt Site Forums The Shop Area Engine Shop Fuel air mixture?

Lately temperatures here in So. California been hitting triple digits.Are most of you Bolters adding a little air to the 1 barrel on the old 235 six cylinders, mine is seeming to run about the same I don't know.I'm just opening her up about a 1/16 of a turn at a time.....?

I have never changed the AF mixture because of the weather and everything always ran well.

My dad said it is not broken don't fix it.

Wrong way- - - -hot air is less dense, so you need to be going leaner, not richer as the temperature or altitude goes up. Opening up the mixture screw increases both air and fuel, so you're giving the engine a richer mixture for no good reason. Set it to the best vacuum reading at idle and leave it alone.
Jerry

Hey, sounds good to me I'll get the ol vacuum gauge out there and check it out. No wonder I can't catch Johnson or Harvick there at the races?

Everyone knows you need more chrome to go fast.

In addition to the highest idle vacuum (always a good starting point), the critical jetting to compensate for high air temperature (and/or high elevation) is done on the main circuit's high-vacuum event. Depending on the type of carburetor, this is controlled by:
1. the main jet size, or
2. a combination of jet size and metering rod diameter (AFB, ThermoQuad, QJ, Edelbrock), or.
3. a combination of main jet size plus power valve channel restriction size (Holley 4150)
The typical R&D is reduce main jet size by 1 number and test cautiously to see if cruising vacuum is increased. If yes, test for knock at full throttle.

I'm just using the old stock G.M. model B 1 barrel carb. rebuilt it about 3 years ago. It runs ok not bad but it seems like it could run better and then again all my pals and gals say they wished theres run that good. I'm not sure about the jet size, rod diameter, power valve like I said I know I can't run with Johnson and Harvick. My question is the only place I can install my vacuum gauge hose is to the port at the carb. that runs over to the vacuum advance at the distributer. Now I've been told this is not where to hook it up? Thanks there Bolters........

I think you're just looking for manifold vacuum. Maybe disconnect the line from the manifold to the wipers and use that for your gauge?

-Michael

This how I showed my son to do it.

IIRC there used to be an aftermarket accessory part that consisted on a std. #2 or 3 SAE 1 bbl. flange 1" thick spacer (aluminum) with a 1/8-27 pipe to 1/4" hose fitting already installed. Goes between the carb and the manifold.

Every 235 I've seen has a manifold vacuum port about 2" below the carb mounting flange for a windshield wiper hose. If there's not one there, a quick drill and tap job in one of the manifold runners going to the front or rear is an easy fix. A 1/8" NPT thread is plenty to install a hose nipple for a vacuum gauge.
Jerry