[Bernica]

Originally Posted by Wbulk

First off that is a great carburetor for the money. If you want to do it right buy a wide band O2 sensor that goes in the dash, but you can just use it as a tool and not put it in the dash. It's a lot cheaper that way. I started tuning with a wide band three years ago and would never, never go back. I use an Innovate #3844 MTX-L that I can also hook my laptop to it and use the charting feature. When you get done just unplug it and put it back in the box and use as a tool for the next car. This last summer I used it to tune a friends show car with an Edelbrock ProFlo 2 Fuel Injection System that he gave up on. Install the bung between the collector and the muffler and tape the wiring on the side of the car and over the door. With a wide band and a vacuum gauge you can tell exactly what circuit you are in and no more guessing.

Do the following one step at a time and the adjust before you go to the next step. If you skip around you can mess up what you just fixed. The circuits are: idle, idle transfer, primary main metering, power circuit, and secondary main metering. The accelerator pump circuit is a whole other issue not addressed here.

1. Idle/ Idle Transfer
Start with your idle circuit, then from about 1300-1800 rpms, depending on the engine, you can check the idle transfer circuit. This carb has small restrictor jets to adjust the transfer circuit. On the Slayer I believe stock restrictors are #32s but I don't think the restrictors are marked like main jets. This is where you get most of you gas mileage from. You are looking for 14-14.7 AFR. Now change restrictors if needed.

2. Primary Main Metering
From about 1,800-2,100 rpms you will be starting the primary main metering. In third gear very slowly open the throttle and run the engine up from 1,800- 3,000 rpms. Take about 30 seconds to do this and watch O2 sensor from 2500-3000 rpms for your primary main metering AFR. Do this with your secondary linkage disconnected. Opening slowly keeps the power valve out of the picture and stabilizes the AFR to get a good reading. You are looking for 13.75-15 AFR about. Change jets if needed.

3. Power Valve Circuit
With a vacuum gauge attached, (I run a long clear plastic tube from Home Depot out the front scoop taped on the hood and over the passenger door). In third gear put your foot in it and when you get below the vacuum rating on your power valve, usually stock is 6.5 in., read what your AFR is. The power valve has two restrictor jets. They are under the power valve and I believe they are not marked, and are #55. You are looking for about 12.75-13.25 AFR. Most are way rich. Change restrictors if needed.

4. Secondary Main Metering
Hook up your secondaries and do some high rpms runs, but make sure your vacuum is above the power valve rating. You are shooting for around 13.5-14.25 AFR.

5. Wide Open Throttle
Lastly do some wide open throttle runs which will open the power valve and the secondaries. Everything will be all in. You are looking for 12.25-12.5 AFR. To keep your speed down you can do this is third gear, but it will still be pretty fast. Don't over rev your engine.

Now the problem is how do you know what restrictors and jets to buy. I go through each of these steps first and see where they are and estimate what I will need doing the math based on percentages. I order the jets and restrictors from Quick Fuel. They seem to be cheapest. Do the testing with a passenger to watch the O2 and vacuum gauge, and do testing on a open road with no traffic. It could take up to a tank of gas. You may have to do this a few times and order more jets.

One hint: Have the passenger use a cell phone and record with video the readings of each step. Say which step you are doing in the recording so you don't get confused. Because these cars are so fast the runs are usually really short. Write down every jet and restrictor change and don't lose track. When you get done you should have a great running carb. I really like the process and just think it's fun to get these dialed in.

Good luck.

This is good stuff! I am about to re-do my exhaust and will plan on putting in the bungs as well! Thanks!