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How to Maintain the Carburetor and Fuel System (6)

Do not forget about the accelerator pump lever adjustment. For oval track use, the pump lever should be adjusted so there is no play in the pump linkage when he throttle is closed. This will assure that there will be no lean stumble when the carburetor comes off idle. Tuning an accelerator pump for maximum performance off the corner often involves reducing, rather than increasing, the pump volume and discharge rate.

 

Accelerator Pump Lever Adjustment

Do not forget about the accelerator pump lever adjustment. For oval track use, the pump lever should be adjusted so there is no play in the pump linkage when he throttle is closed. This will assure that there will be no lean stumble when the carburetor comes off idle. Tuning an accelerator pump for maximum performance off the corner often involves reducing, rather than increasing, the pump volume and discharge rate.

 

Drag racing calls for a slightly different approach. For the hardest starting line launch with a foot brake, the pump lever override spring should be adjusted so that fuel starts to discharge through the nozzle at an engine speed lower than launch RPM. If a car leaves the starting line at 5000 RPM, the pump shot should begin at 4700-4800; an 1800 RPM launch calls for the accelerator pump shot starting at 1500. The key is to have no slop in the accelerator pump system at starting line RPM, so that the pump shot is not "used up" below that RPM. Although adjusting the accelerator pump as described will create a lot of slop in the pump linkage at idle, (and may produce a stumble when driving in the pits) a car will leave harder. Drag cars equipped with a stick shift or transbrake, where starting line launch is accomplished with the carburetor wide open, requires adjusting like an oval track application.

 

Float Level Adjustment

When assembling a carburetor or reinstalling the fuel bowls, you need to adjust the float to be approximately 0.450" from the top of the bowl (in line with the bowl screw bosses when the bowl is upside down). This "dry" setting is to get you in the ball park. Recheck the float level with the engine running and the sight plugs out. Fuel should just wet the outside of the bowl as the fuel seeps out. On the secondary side, where the sight plug is lower, fuel level should be slightly higher. On Demon carburetors, the large, patented sight glass windows allow float level setting without having fuel escape from the float bowl. You can adjust the float level relative to the three cast-in marks next to the float window.

 

Power Valve Tuning

The power valveŭs function is to supply extra fuel for wide- open throttle, high load conditions. When manifold vacuum falls below the vacuum level stamped on the power valve, the power valve opens and enriches the main circuit by about six to ten jet sizes. This occurs under high engine loads such as full throttle. The power valve number should be at least 1.5-2.0 in/hg of vacuum under engine idle vacuum. If an engine produces 8.0-9.0 in/hg of vacuum, a 6.5 power valve would be a good first selection. Using a power valve with a rating lower than this will delay the enrichment and can cause hesitation. However, on an oval track car with restricted carburetor rules, using a power valve with a lower rating can sometimes help performance coming off corners. Any drag race carburetor with a secondary power valve must be turned sideways to avoid fuel starvation. The power valve is higher than the jets and is the first to be uncovered as fuel is pushed to the rear of the float bowl. Since there is no way to put an extension on the power valve, the carburetor must be turned sideways to eliminate fuel starvation.

Find out more about GM carburetor by visit miparts.com.

Source: Free Articles from ArticlesFactory.com

ABOUT THE AUTHOR


Olivia Tong is the freelance writer for e-commerce website tahiko.com and miparts.com offers the buyers around the world to find quality and discount auto parts. We try our best to aggregate leads in the business world, and let these leads benefit the entire business person.



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