Are you experiencing a sooty exhaust, excessive carbon buildup, or black engine oil in your classic car? If you’re running SU carburetors, the issue might be an improperly tuned fuel-air mixture. For years, mechanics have relied on methods like lifting the piston to adjust carburetors, but with modern fuels, these techniques often fall short, leading to rich running conditions and engine problems.
I’ve personally encountered this issue with my own 3.5lt Mk 4, discovering alarming carbon deposits despite using traditional tuning methods. This experience led me to explore a more effective approach – the Barry Obitz method. A friend, an ex-RAA technician, shared this technique, and I’ve found it to be a far superior “tool” for achieving a stoichiometric fuel-air mixture in older vehicles. This method, while unconventional, is remarkably simple and effective for checking and adjusting your fuel-air mixture.
The traditional “finger in the exhaust” test can be a starting point. If your finger comes out black after a short engine run, it’s a clear indicator of a rich fuel mixture and a need for adjustment. But how do you fine-tune it for optimal performance with today’s complex fuels?
Why Traditional Carb Tuning Methods May Not Suffice
In the era of leaded fuel, a light grey exhaust color was often a sign of a well-tuned engine. The traditional method of briefly lifting the carburetor piston to observe engine response worked reasonably well. However, modern fuels, with their intricate blend of hydrocarbons, behave differently. This can result in inaccurate readings when using older tuning techniques, often leading to a fuel mixture that’s too rich. The consequences of a rich mixture are significant:
- Carbon Buildup: Excess fuel leads to carbon deposits in the combustion chamber, on pistons, and valves. In my case, this resulted in a thick layer of carbon on the piston tops, with edges threatening to break off and damage the valves.
- Sooty Exhaust: A black, sooty exhaust is a visible sign of unburnt fuel, indicating a rich mixture.
- Black Engine Oil: Fuel dilution can cause engine oil to become black and contaminated quickly, reducing its lubricating properties and engine life.
The Barry Obitz Method: Your Paper Tool for Fuel Air Mixture
The Barry Obitz method offers a practical and surprisingly effective way to tune your carburetor for the ideal fuel-air mixture. This method utilizes a simple piece of paper as your primary “tool” for checking the exhaust output and making precise adjustments.
Here’s how it works:
- Prepare a Paper Strip: Take a piece of paper (newspaper or similar works well) and attach it to a clothes peg.
- Position the Paper: Hang the paper from your car’s rear bumper so that it is positioned directly in the exhaust stream.
- Listen to the Exhaust: Start your engine and let it reach operating temperature. As the engine runs, listen carefully to the exhaust note and the sound of the paper fluttering. You’ll be listening for a “cracking” or “popping” sound, which indicates misfires due to an incorrect fuel mixture.
- Gradual Carburetor Adjustment: Slowly and gradually adjust your carburetor mixture screw. In small increments, lean out the mixture (reduce fuel). After each adjustment, listen to the exhaust and observe the paper.
- Minimize the Misfire Sound: The goal is to adjust the carburetor until the “cracking” sound of the paper under misfire is reduced to an absolute minimum. When this occurs, your engine is running as close as possible to the stoichiometric ideal fuel-air ratio.
This method focuses on minimizing misfires, which are more pronounced when the fuel mixture is slightly off. By using the paper and your hearing, you’re effectively using a sensitive “tool” to detect subtle changes in engine combustion.
Benefits of the Barry Obitz Method
After adopting the Barry Obitz method, I experienced significant improvements in my engine’s performance and condition. The benefits are clear:
- Cleaner Engine Oil: The engine oil remains cleaner for longer periods, indicating less fuel blow-by and better combustion.
- Cleaner Spark Plugs: As shown in the images, the spark plugs are no longer sooted up, reflecting a more efficient and complete combustion process.
IMG_E2111 spark plugs after tuning with Barry Obitz method showing cleaner condition
- Reduced Carbon Deposits: By achieving a more accurate fuel-air mixture, you minimize carbon buildup, contributing to improved engine longevity and performance.
- Improved Fuel Efficiency: A stoichiometric mixture ensures that fuel is burned efficiently, potentially leading to better fuel economy.
- Easy and Accessible Tool: The “tool” required is simply a piece of paper and a clothes peg, making this method incredibly accessible to any car enthusiast, regardless of their tool collection.
IMG_E2144 exhaust pipes showing cleaner condition after Barry Obitz tuning method
After a 100km run combining urban and country driving, a simple finger check inside my exhaust pipes now reveals a level of cleanliness comparable to modern cars. This is a stark contrast to the sooty conditions I experienced before using the Barry Obitz method.
IMG_E2146 exhaust finger test showing improved cleanliness after fuel air mixture adjustment
Conclusion: A Practical Tool for Fuel Air Mixture Tuning
The Barry Obitz method, utilizing just a piece of paper as a “tool for checking fuel air mixture on car”, offers a remarkably effective and accessible way to fine-tune your carburetor, especially on classic cars running SU carbs and modern fuels. It’s a testament to simple ingenuity and practical experience in automotive maintenance. If you are looking for a straightforward way to improve your engine’s performance, reduce carbon buildup, and ensure a more optimal fuel-air ratio, give the Barry Obitz method a try. You might be surprised at how effective this low-tech “tool” can be.
