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Old 04-07-2010, 06:15 AM
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hesitation

I just recently purchased my first Muscle Car and have a few questions.

I have a 454 30 over 300 Stall with Edelbrock Thunder series 800 CFM with electric choke, Howards Cam int. 575 exh. 575.

My questions are:

1. If I am at a dead stop or driving I have a little hesitation if I out my foot into it once past the hesitation it really goes but I was concerned what this could be.

2. When starting the car it seem like I really need to crank it and pump the gas to get it started. It this normal? Or does it sound like a possible carb. issue. (do I really need the electric choke?)

Any help would be great!!

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Old 04-07-2010, 07:45 AM
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Move the throttle accelerator pump linkage arm to the inner hole to max the pump shot. May need a larger accel shooter.

The idle and throttle response will be much better if the distributor advance curve is set up.

26++ initial at idle 36-38deg at max mech advance.
Some people just lock out the mech adv and run full locked timing with big duration cams.

10-12 deg of vac advance for cruising.

Block off the manifold heat riser passages and install a wood carb spacer to keep the carb cool.
The carb body is getting too hot.
Limit idle fuel pressure to 5psi.

Last edited by F-BIRD'88; 04-07-2010 at 07:54 AM.
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Old 04-07-2010, 05:01 PM
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Quote:
Originally Posted by 1966 CHEVELLE
I just recently purchased my first Muscle Car and have a few questions.

I have a 454 30 over 300 Stall with Edelbrock Thunder series 800 CFM with electric choke, Howards Cam int. 575 exh. 575.

My questions are:

1. If I am at a dead stop or driving I have a little hesitation if I out my foot into it once past the hesitation it really goes but I was concerned what this could be.

2. When starting the car it seem like I really need to crank it and pump the gas to get it started. It this normal? Or does it sound like a possible carb. issue. (do I really need the electric choke?)

Any help would be great!!
The hesitation is probably not enough accelerating pump shot and or the mixture is a little overall lean and or the power step on the metering rods isn't coming up fast enough. Of these three the one in common with getting the engine started is the lean mixture.

You didn't specify whether the hard starting is hot or cold starts. These can be very different issues.

Hard to start cold:
- Fuel leaving the float bowl, can be cooked out after a hot shut down, or leak out thru a crack in the casting. The carb should have an insulating spacer between it and the manifold so it doesn't heat soak the carb after a hot shutdown.

- Fuel pump doesn't provide sufficient fuel when cranking. This is usually leaky valves inside the pump, inadequate stroke of the pump, air leak into the fuel line, plugged fuel filter.

- Float level not set high enough. This could be common with your hesitation and hard starting.

- Too much choke, this is the opposite of the mixture resulting in the first problems which will be lean, this will be way rich if the choke is too tightly closed. The Edlebrock came with adjustment instructions that should be followed. The choke is a necessary evil on street driven engines, it is intended to force an over-rich mixture into the cold engine such that there is enough fuel so that a large enough percentage of the stuff will evaporate and burn in the cylinders so the engine will run and do so unattended. The unburnt portion of fuel washes oil off the cylinder walls increasing wear and gets into the crankcase to dilute and contaminate the oil, and/or goes out the exhaust to pollute the environment as raw hydro-carbons; all of this is costing you money. Without a choke you just fiddle the throttle to operate the accelerating pump to the same end, so removing the choke function buys nothing and requires your continuous presence to mess with the throttle. It's important to get the engine warmed up as quickly as possible. To that end the intake is usually heated by exhaust gases, this improves vaporization of the fuel which in turn reduces how rich the start up mixture has to be and how long you have to use it to get the engine to run smoothly and cleanly. This reduces upper cylinder fuel wash, oil contamination, and the amount of pollution going out the tail pipe all of which is your hard earned money leaving without doing any work. Leave unheated manifolds where they belong, on race cars and in dyno rooms. If you have an unheated intake manifold, it is wise to used a stove over the exhaust to preheat the incoming air then dump that air into the carb. There are many factory air-cleaner systems out there that do this. The advantage is heat to get the engine warmed up quickly that can be shut off when no longer needed.

- The other important thing is a coolant bypass, this functions to circulate coolant thru the engine when it's cold and the thermostat is closed. This prevents pump cavitation, hot spots in the head, and greatly speeds warming the engine which reduces internal wear, improves power output, is easier on the environment and your wallet.

Hard to start hot:

- Fuel boiling in the line between the pump and tank. This fuel is under a reduced pressure caused by the drawing action of the pump, it becomes easy for it to change states to a gas which the pump can't pump.This is vapor lock.

- Fuel boiling out of the carb when shut down hot. You may get a light off the accelerating pump then just a grind till the fuel pump can put something in the float bowls. Or there may be so much fuel in the cylinders that you can't get a light till they are dried out. A solution is an insulating spacer between the carb and manifold.

- Fuel leaking from cracks or porosity in the carb casting.

- Choke doesn't open when engine is hot, resulting in a lack of air and excessive fuel to the engine. Adjust to manufacturer's instructions, be sure the choke is operating with a full 12 volts and is not sourced off the ignition system which could reduce its voltage. When the engine is hot, it may take a moment or two for the choke to react, it is electric and as such is operating independent of engine temp, it has its own electric heater and needs time to "catch" up with events when the engine is hot.

- Too much initial advance making it hard for the starter to turn the engine over hot compression. A back side of this is that the starter sounds normal but is using so much current so there isn't enough left to run the ignition system so the spark is weak to non existent.

Bogie

Last edited by oldbogie; 04-07-2010 at 05:14 PM.
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