Bristol, a city steeped in automotive history, is a natural hub for car enthusiasts. For owners of classic cars like the Arnolt Bristol, finding expert Car Tuning In Bristol is crucial. This guide, based on advice from Arnolt Bristol expert Jim McQuay, provides essential information on ignition timing, spark plugs, and carburetor adjustments for these unique vehicles.
Proper tuning ensures optimal performance and longevity. According to the Arnolt Bristol owner’s manual, static ignition timing should be set at 5 degrees before top dead center (BTDC) with the ignition fully retarded. The contact breaker gap should be between .010 and .012 inches. This is a narrower gap than found in many other vehicles.
Spark Plug Recommendations for Arnolt Bristol
Original Arnolt Bristols used KLG P10L80 single-piece spark plugs. Suitable substitutes include Champion Z9 or Z10, and NGK C6E or C7E. Remember that a “6” heat range is hotter than a “7”. These alternatives are all 10mm plugs with a 5/8-inch head size and a 3/4-inch reach. The recommended spark plug gap, as per the manual, is .018 to .020 inches.
Carburetor Adjustments: Arnolt Bristol Tuning
For Arnolt Bristols operating below 3000 feet altitude with the original jetting, carburetor adjustments should be minimal. The vehicle utilizes three carburetors, each with two idle screws. One screw controls idle speed, aiming for 750 to 900 RPM. All three carburetors must be synchronized to draw equal amounts of air. This can be achieved using a unisyn tool, a manometer, or by carefully listening to each carburetor intake with a hose.
The second idle screw, located to the left of the throttle stop, is the slow-running adjustment screw. The manual recommends placing a piece of paper under each slow-running screw, tightening until slight resistance is felt upon removing the paper, and then turning the screw inward one additional turn. Begin this process with the center carburetor.
Fine-Tuning the Mixture: Arnolt Bristol Carburetors
The mixture control screw, positioned to the right of the slow-running screw, fine-tunes the idle mixture. Initially, turn this screw out one full turn. Turning it clockwise (in) leans the mixture, while turning counterclockwise (out) richens it. Note that this is the opposite function of Amal motorcycle carburetor screws. Adjustments beyond idle mixture are made by changing jets.
Altitude Considerations for Arnolt Bristol Tuning
Higher altitudes require leaner main jets and corresponding air bleed jets. Generally, reduce the main jet size by one for every 3000 feet of elevation. Ensure the engine reaches 70 degrees Celsius before adjusting the carburetors. Proper valve seating and minimal valve guide wear are also critical.
Troubleshooting Tips: Prioritizing Ignition
In many cases, poor engine performance stems from ignition issues. While not always the culprit, the ignition system is a good starting point for troubleshooting unless a different problem area is known.
This guide provides a foundation for car tuning in Bristol, specifically for the Arnolt Bristol. However, consulting with experienced mechanics specializing in classic car tuning in Bristol is always recommended for complex issues or major adjustments.
