# Rough Idle, Occassional Miss, Choke



## Koppster (Jul 27, 2008)

Friends

Car ran fine Tuesday and Wednesday but yesterday I started having choke, idle and slight miss issues.

76 400/Edelbrock 800CFM Performer carburetor/RPM Performer Heads, intake and cam

Choke doesn't seem to kick in at all, idle rough or won't idle even when warm, get an occassional miss/buck even at RPM; however, it runs strong when I accelerate

I poked around under the hood yesterday, didn't see any broken or disconnected wires or vacuum hoses

Thoughts?

Thanks

Rick


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## geeteeohguy (Feb 2, 2008)

Sounds like a vacuum leak to me. Check the choke. With a cold engine, it should close when you hit the gas pedal. If not, adjust it or free it up. IS the car running too rich? (black smoke, fuel smell) you could have a float/needle/seat issue. If you get it running, but it runs rough, does it smooth out when you put your hand over the carb, or drizzle a little carb cleaner into the carb? If so, it's too lean, and needs adjustment. Carbs generally are reliable. Any sudden change in idle quality, etc. usually indicates a vacuum leak or float-circuit issue. Double check all the vacuum lines, and the carb base gasket. Don't forget the PCV, either.


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## Koppster (Jul 27, 2008)

Jeff

I don't have any trouble starting it; however, it won't idle until it warms up and even then it's not a good idle that I can trust, especially in traffic and there's that occassional miss/light buck when acclerating. 

Acts like the choke is not engaging, temperatures are warm here so I'm ass-u-me'ing the choke is not critical to start up. I have to sit in the car for about 5 minutes for it to idle and then it's a low RPM loping idle that I don't trust.

Car accelerates so I have discounted fuel pump and fuel filter concerns.

However, even when it gets to operating temperature (195) there is still a light miss/soft buck and I can't trust it to idle, have to rev to keep it running when I let off the gas.

So far I have not been able to find a vacuum leak, going to take a water bottle out this morning and I'm going to watch the choke to see if it works.


Not sure what role the choke would play after the car warms up; however, with our current moderate temperatures it takes quite a while for the car to get to 195.


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## Koppster (Jul 27, 2008)

Okay...here's some observations, just came back from the garage:

Carb is an Edelbrock Performer 800 CFM w/ Electric Choke

1. Pulled the air cleaner, choke plate was closed with the engine off
2. Started the motor and choke remained closed, typical high idle
3. Gave it a quick rev and the choke disengaged (opened completely) and did not reengage, idle rough, dropped to about 500 RPM
4. Started several more times playing with the choke plate, car would idle if I manually held the choke closed, and it would idle as long as I did not rev the motor
5. Choke operation did not change if I disconnected the hot/red wire, verified voltage present (read 19.5VDC, that surprised me)
6. As long as I did not "pop" the accelrator the car would retain idle at about 900 RPM, if I popped the acclerator it would drop down to around 500
7. Sprayed every vacuum connection I could find with windex, no bubbles, PCV valve rattles nicely

This is new for the car, did not act like this until this week. Seems to me it's the carb or the choke. What I really don't get is why it will settle at 900 RPM until you give it a sharp rev then it drops to 500...I can also push the linkage and get it to drop :confused

Choke? If so, why does the problem persist when engine warms
Something else? Accelerator pump?

Thanks in Advance
Rick

PS: Interesting, possibly related thread? http://forums.performanceyears.com/forums/showthread.php?t=599377&highlight=edelbrock+electric+choke


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## geeteeohguy (Feb 2, 2008)

Rick, it sounds to me like the base idle screw is coming all the way off the fast idle cam on the carb linkage. Look closely at the base idle screw when it IS idling at 900 rpm. Goose the throttle, and see if the cam moves a little, allowing the idle to drop. May be gummed up linkage. All you need to do is clean it and re-set the base idle speed. VOLTAGE: check it again, and check the scale on your voltmeter or get another one. At 19.5 volts in your charging system, you should be blowing headlamps and boiling your battery dry. You never want to see more than about 14.5 or 15 volts with these cars. If you really DO have that kind of voltage, it can affect the ignition circuit in a bad way. 
That MAY be the problem. Have you checked your points/cap/rotor/wires/plugs?
Here's what I would do on your car in this order: Verify charging system voltage. Verify fast idle cam/throttle binding and clean , lube, re-set. Determine cause of ignition misfire when driving the car. Check the ign wires, points, dwell, check the plugs. Why is it misfiring? Your choke is obviously working. You can also do a cranking vacuum test or put a vacuum guage on the engine and see if it's holding steady. If it flickers back and forth rapidly, you have a mechanical problem. The base idle setting has NOTHING to do with a bucking/missing while driving the car down the road. Keep us posted.


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## Koppster (Jul 27, 2008)

*pictures*

Pictures in case anyone spots anything


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## geeteeohguy (Feb 2, 2008)

Rick...what the heck happened to the linkage at the base idle screw? It's got the bejeezus bent out of it. The base idle screw is the one most forward, shown in the first picture. The arm on the cam is twisted like a pretzel. Not good.


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## Koppster (Jul 27, 2008)

geeteeohguy said:


> Rick...what the heck happened to the linkage at the base idle screw? It's got the bejeezus bent out of it. The base idle screw is the one most forward, shown in the first picture. The arm on the cam is twisted like a pretzel. Not good.


You're talking about the ear just above/behind where the cable connect I ass-u-me?

Anybody else have any thoughts? Rukee?


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## Rukee (Feb 8, 2007)

When cold the choke plate should be spring loaded. With the throttle slightly open, if you stick your finger into the choke plate to open it, it should close again under spring pressure. If not, then the electric choke element may be bad.
And I agree about the bent linkage, know how it got bent up?
To check for a vacuum leak, after it's warmed up and engine running, cover the top of the carb with your hand choking out the motor, if the RPMs increase at all, you have a vacuum leak somewere. If the motor dies right out when you cover it, you have no vacuum leaks.


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## GroundHog (Oct 16, 2009)

That's a simple method, I might give that a try. 

I don't have the idle problems, but I have the exact hesitation problem you're describing. Idles fine and everything sounds normal but when I slowly accelarate from a stop the car starts going a few feet, then hesitates/chugs for a second, then starts accelerating normally. When I stomp it from a roll though, it accelerates just fine with no hesitation.


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