Car carburetor tuning

Category: Auto Tuning

Carburetors or carbs were once commonly used on almost all car engines. Carbs come in all different types. The purpose of all carbs is simply to control the fuel going into the engine. The downdraft or draw through throttle plate carb was most widely used on passenger cars. These carbs usually consist of a low speed circuit used for low rpm or idle. Sometimes on the slightly more advanced carbs there are mid range circuits. The accelerator pump circuit assists in acceleration. The main jets are used the most and are very important to full throttle tuning. All production vehicle carbs (quadrajet, carter)usually have a choke circuit for warm up assist. Let’s start with the carburetor’s choke system. The choke operates usually by restricting the air into the engine. Along with changing the fuel to air ratio the manifold vacuum increases significantly, pulling even more fuel from the low speed circuit. The carb needs to run rich (alot of fuel) when the car first starts up because the engine isn’t warm enough to help vaporize the fuel. The carb uses idle, low speed or pilot jets (which are the same things) and air bleed screws to control the amount of fuel being sucked in at idle. The air bleed screws lean out the mixture as they are rotated out. Idle tends to be slightly richer than stoichiometric (perfect fuel to air ratio) of 14.7 to 1.

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EGR location and troubleshooting

Category: Auto Tuning

EGR stands for exhaust gas recirculation. The EGR valve will generally make the car run poor at lower speeds or idle, but can effect it anywhere. The valve should not open at idle. Operate at midrange speeds and quit again before wide open throttle. The egr valve is usually located on the intake manifold or head. There is a diaphram in the egr valve. The valve uses manifold vacuum on the diaphram to lift or close a valve allowing exhaust gas to enter the intake manifold. An easy test for the diaphram is to remove the vacuum line that runs to the egr valve. You can normally reach the diaphram area with your finger. Move this opposite from the direction it normally sits at. Then cover the vacuum port located on the egr valve with a plugged hose or your finger. The diaphram should either stay in this other position or slowly move to the normal position. If it won’t hold vacuum and instantly returns to it’s origional position, either a vacuum port is still not plugged or the diaphram is leaking. If it is leaking replace the egr valve. If the egr valve holds vacuum then remove the valve from the manifold.

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