1999 Chevrolet Silverado 1500 Logo
Posted on Oct 28, 2009
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I have 1978 chev pickup with a 350 engine. but will not idle right.i relaced all the sparkplugs,sparkplug wires,condencer,module,cleaned the carb,new vaccum lines.

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john h

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  • Chevrolet Master 29,494 Answers
  • Posted on Oct 28, 2009
john h
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Check pcv -recheck carb idle mixture -air/vacuum leaks in carb or lines-double check ur tune up parts

Greg Bernett

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  • Chevrolet Master 2,993 Answers
  • Posted on Oct 28, 2009
Greg Bernett
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The problem is two things...

1. Air/Fuel mixture

2. Rich/Lean Mixture

Both on the base of the carburetor...they are the two common screwdriver type screws you see at the front of the carb.

You might be running too lean if the engine dies while idling.
How to Lean Out or Richen a Nitro RC Engine tuning and adjusting the fuel/air mixture involves adjusting the high-end (high speed / engine temperature) and low-end (low speed / idle speed) needles on the carburetor. This is also called dialing in your engine. There are usually base-line settings for each nitro engine that provide a good starting point for adjusting the needle settings. You'll turn each needle in very small increments to lean out or richen the fuel.
Turn clockwise to lean out or add air and counterclockwise to richen or add fuel. The low-end needle controls idling and low speeds. The high-end needle controls how the engine accelerates and runs at high speed and has a greater effect on engine temperature.

Problem: My Motor Hesitates, Backfires, And Won't Hold A Steady Idle.
Solution:
Many hot rodders crank up the idle circuit to richen up the air/fuel mixture in this situation, but that's the last thing you want to do. Chances are these symptoms are caused by too much cam and not enough timing. "Big cams and compression don't produce much cylinder pressure at idle, so there's no way a motor will run properly with only 8 degrees of initial timing," says Vrbancic. "You can't expect a performance motor to run well with the same timing as with a stock camshaft. Simply turning the timing up to 15 degrees to compensate for the low vacuum usually fixes the problem entirely."

Check out this link for really good help!
http://www.chevyhiperformance.com/techarticles/0810chp_chevy_carburetor_tuning_tips/index.html

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  • Master 407 Answers
  • Posted on Oct 28, 2009
Anonymous
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Carb problem or vacuum leak at carb base gasket or intake manifold

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Cuts out under load. 78 chevy pickup. 1/2 ton 4X4. 350 engine. Idles perfect, starts right up. When you get on the gas hard, it sputters and cuts out. New spark plugs and wires, fuel pump and filter.

Some things you can check. First, with the engine off, look down into the carburetor and quickly move the throttle. You should see a squirt of fuel. If not, the accelerator pump is bad. If that is OK, check the spark itself. It should bridge a half inch gap with no problem and should be healthy (have good "snap" and bluish color). If OK, check the two wires that run from the ignition module inside the distributor, down under the breaker plate.Often those wires can partially break or short to the housing...when the advance moves the plate it will cause a problem.
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Backfiring

No. If you knocked pieces of the chain or sprockets off, you'd not run at all. Check your timing and your idle mix. Also, check to see if your crankcase vent valve is moving freely. Replace if in doubt. Sounds like you may be running rich. Check carb for proper idle mix after you set float levels. Is the carb new, rebuilt or some old hunk? Are the gaskets new or reused? Is the spacer plate the right one for the car and installed correctly?

Also...was the timing chain new and the cam properly indexed? You may have to take the front of the engine apart to find out.
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