Missing on initial start up...
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Joined: May 2007
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From: Orlando FL
Missing on initial start up...
I solved a fuel starvation problem by replacing the fuel pump. Now when I start the car when it's cold the engine stumbles and is missing badly. When I depress the gas pedal the miss follows the revs. After ~2 minutes the idle evens out then it drives and idles great. Any ideas? Is it a coincidence that this issue occurred right after I replaced the fuel pump?
This issue did not exist before I replaced the fuel pump. I replaced the spark plugs and plug wires but the problem still exists.
Thanks in advance!
This issue did not exist before I replaced the fuel pump. I replaced the spark plugs and plug wires but the problem still exists.
Thanks in advance!
Team Owner
Joined: Aug 2006
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From: Columbia Missouri
The rough idle for a few minutes indicates a badly adjusted choke. It wouldn't have anything specifically to do with the fuel pump change, but it's something to check out.
Also, did you clean the carb filter and make sure any inline filters are clean as well?
Also, did you clean the carb filter and make sure any inline filters are clean as well?
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From: Wellington, FL
St. Jude Donor '11 thru '25
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From: Orlando FL
I checked the fuel filter at the carb as part of my diagnosing the bad fuel pump. The filter was clean then, and it's still clean now. That's the only filter (aside from the sock in the tank).
I have the Chevrolet Service Manual for '77 (my car is a '77). They talk about the choke a lot. Is there a certain area of the choke that I need to check?
The miss/stumble only happens when I start the car in the morning. If I drive it to work, I don't get the miss/stumble when I start it up after work.
Team Owner
Joined: Aug 2006
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From: Columbia Missouri
Pull the air filter off when the engine is cold in the morning, and check to see if the choke blade is fully closed. If not, pull the throttle once, and see if it closes. If not, you need to re-adjust it so it's closed when cold and open when warm.
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From: Orlando FL
Is the car running too rich at start up?
This is the original carb and it still has the original choke coil cover. According to the '77 GM Service Manual, there should be an alignment mark on the cover between the words "Rich" and "Lean". I don't see a mark on my cover. Do I assume that the mark is between "Rich" and "Lean" on the cover? If so, the mark would be about 45 degrees counterclockwise (toward the rich) from the alignment marks on the choke coil housing. Does this have anything to do with my stumbling problem?
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From: Wellington, FL
St. Jude Donor '11 thru '25
I went out this morning and the choke blade is fully closed. I started the car and the engine was stumbling. I found that if I opened the choke blade all the way up with my hand, the car idled better. After ~2 minutes the car was fully warmed up and idled normally and the choke blade was fully open without me having to open it with my hand. Also, the exhaust smells really smokey.
Is the car running too rich at start up?
This is the original carb and it still has the original choke coil cover. According to the '77 GM Service Manual, there should be an alignment mark on the cover between the words "Rich" and "Lean". I don't see a mark on my cover. Do I assume that the mark is between "Rich" and "Lean" on the cover? If so, the mark would be about 45 degrees counterclockwise (toward the rich) from the alignment marks on the choke coil housing. Does this have anything to do with my stumbling problem?
Is the car running too rich at start up?
This is the original carb and it still has the original choke coil cover. According to the '77 GM Service Manual, there should be an alignment mark on the cover between the words "Rich" and "Lean". I don't see a mark on my cover. Do I assume that the mark is between "Rich" and "Lean" on the cover? If so, the mark would be about 45 degrees counterclockwise (toward the rich) from the alignment marks on the choke coil housing. Does this have anything to do with my stumbling problem?
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From: Orlando FL
I can't figure out how to make the choke blade open wider at initial start up. As it is, it opens about half way. If I open the choke blade all the way with my hand the car idles much better at start up.
Per the manual I adjusted the choke linkage so that the choke blade closes fully before the car is started. I then rotated the choke coil cover to watch the choke blade open and close. I then tightened down the choke coil cover right when the choke blade just closes. I tried to start the car and now it idles worse than before until I manually open the choke blade with my hand.
Can anyone give me some advice in a language I can understand? The Service Manual is written for mechanics, which I am not. I'm proud of myself when I successfully change the oil!
Per the manual I adjusted the choke linkage so that the choke blade closes fully before the car is started. I then rotated the choke coil cover to watch the choke blade open and close. I then tightened down the choke coil cover right when the choke blade just closes. I tried to start the car and now it idles worse than before until I manually open the choke blade with my hand.
Can anyone give me some advice in a language I can understand? The Service Manual is written for mechanics, which I am not. I'm proud of myself when I successfully change the oil!
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Race Director
Joined: Sep 2001
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From: Wellington, FL
St. Jude Donor '11 thru '25
I can't figure out how to make the choke blade open wider at initial start up. As it is, it opens about half way. If I open the choke blade all the way with my hand the car idles much better at start up.
Per the manual I adjusted the choke linkage so that the choke blade closes fully before the car is started. I then rotated the choke coil cover to watch the choke blade open and close. I then tightened down the choke coil cover right when the choke blade just closes. I tried to start the car and now it idles worse than before until I manually open the choke blade with my hand.
Can anyone give me some advice in a language I can understand? The Service Manual is written for mechanics, which I am not. I'm proud of myself when I successfully change the oil!
Per the manual I adjusted the choke linkage so that the choke blade closes fully before the car is started. I then rotated the choke coil cover to watch the choke blade open and close. I then tightened down the choke coil cover right when the choke blade just closes. I tried to start the car and now it idles worse than before until I manually open the choke blade with my hand.
Can anyone give me some advice in a language I can understand? The Service Manual is written for mechanics, which I am not. I'm proud of myself when I successfully change the oil!
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From: Orlando FL
I would just keep opening the choke with the adjustment until it starts and runs properly. Try it first with the engine running. In any event, you do want to have a clean start the next time and by that I mean to fully warm it up after each adjustment so that when you start it cold again, the cylinders aren't full of gas from the last start. There is probably a better way, but that is how I would do it. Stay with it and you will get it. BTW, I assume that the engine is properly tuned and that the plugs aren't fouled from this heavy choke situation. You may want to check them.
When you say "opening the choke with the adjustment" do you mean rotating the choke cover further toward the Lean side?
The engine was rebuilt ~3000 miles ago. It was starting and idling fine until a month ago when the fuel pump went. I replaced the fuel pump and it runs great again after it is warmed up (maybe even better than before the pump went). But the trouble I'm now having is running rich at start up. The first thing I did when it started idling bad at start up was to replace the plugs and wires. The old plugs were in good shape after I pulled them but I replaced them anyway.
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From: Wellington, FL
St. Jude Donor '11 thru '25
Thanks for your continued support!
When you say "opening the choke with the adjustment" do you mean rotating the choke cover further toward the Lean side?
The engine was rebuilt ~3000 miles ago. It was starting and idling fine until a month ago when the fuel pump went. I replaced the fuel pump and it runs great again after it is warmed up (maybe even better than before the pump went). But the trouble I'm now having is running rich at start up. The first thing I did when it started idling bad at start up was to replace the plugs and wires. The old plugs were in good shape after I pulled them but I replaced them anyway.
When you say "opening the choke with the adjustment" do you mean rotating the choke cover further toward the Lean side?
The engine was rebuilt ~3000 miles ago. It was starting and idling fine until a month ago when the fuel pump went. I replaced the fuel pump and it runs great again after it is warmed up (maybe even better than before the pump went). But the trouble I'm now having is running rich at start up. The first thing I did when it started idling bad at start up was to replace the plugs and wires. The old plugs were in good shape after I pulled them but I replaced them anyway.
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From: Orlando FL
But now I have a new problem. I drove the car to work today and it's running great. It has an automatic transmission, and on my way to work I floored it to get through a yellow light. When the transmission kicked down, the engine stumbled for a couple of seconds before it caught and accelerated. I looked in my rear view mirror and saw black smoke. This only happens at WOT. What is it this time?
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From: Wellington, FL
St. Jude Donor '11 thru '25
I took your advice and started the car when the motor was cold. I rotated the choke cover toward the lean side until the idle smoothed out, which was almost all the way clockwise. This morning I started the car and it now idles great!
But now I have a new problem. I drove the car to work today and it's running great. It has an automatic transmission, and on my way to work I floored it to get through a yellow light. When the transmission kicked down, the engine stumbled for a couple of seconds before it caught and accelerated. I looked in my rear view mirror and saw black smoke. This only happens at WOT. What is it this time?
But now I have a new problem. I drove the car to work today and it's running great. It has an automatic transmission, and on my way to work I floored it to get through a yellow light. When the transmission kicked down, the engine stumbled for a couple of seconds before it caught and accelerated. I looked in my rear view mirror and saw black smoke. This only happens at WOT. What is it this time?
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From: Orlando FL
It happened both times I tried it this morning.
I only live 3 miles/10 minutes from my office and use surface streets where the max speed limit is 45mph. Maybe the car isn't fully warmed up but I've never had the car behave like this before. It ran great at half throttle, the stumble only occurs when I floor it.
I only live 3 miles/10 minutes from my office and use surface streets where the max speed limit is 45mph. Maybe the car isn't fully warmed up but I've never had the car behave like this before. It ran great at half throttle, the stumble only occurs when I floor it.
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From: Wellington, FL
St. Jude Donor '11 thru '25
If it were my car, John, before I do anything else to it, I'd take it out on the highway and run it for a while. Get it fully warmed up and run it at 70 mph or so and punch it every so often at wot for a few seconds and see if the problem clears up (don't get a ticket). I'm just wondering if your plugs might be fouled somewhat. One thing I can tell you is that the 10 minute trip to work is very hard on a car as it is not getting warmed up. This can create sludge in the engine and shorten the life of plugs and the exhaust system.
Drifting
Joined: Aug 2005
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From: League City TX
I bet both problems you have been having have the same cause.
When the engine is cold the choke closes obviously.
When you start the engine the choke is opened a small amount by the
choke pull off diaphram that is mounted to the side of the carb.
This gives the engine enough air to run well untill it gets warm.
If its not functioning then the engine will run poorly until the choke gets warm enough to open.
That same pull off also has a rod from it that connects to the secondary air valves.
It controls the rate that they can open. I think your pull off is bad.
Your black smoke and stumble is being caused by your secondary air valves flopping open too fast.
When the engine is cold the choke closes obviously.
When you start the engine the choke is opened a small amount by the
choke pull off diaphram that is mounted to the side of the carb.
This gives the engine enough air to run well untill it gets warm.
If its not functioning then the engine will run poorly until the choke gets warm enough to open.
That same pull off also has a rod from it that connects to the secondary air valves.
It controls the rate that they can open. I think your pull off is bad.
Your black smoke and stumble is being caused by your secondary air valves flopping open too fast.
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From: Orlando FL
If it were my car, John, before I do anything else to it, I'd take it out on the highway and run it for a while. Get it fully warmed up and run it at 70 mph or so and punch it every so often at wot for a few seconds and see if the problem clears up (don't get a ticket). I'm just wondering if your plugs might be fouled somewhat. One thing I can tell you is that the 10 minute trip to work is very hard on a car as it is not getting warmed up. This can create sludge in the engine and shorten the life of plugs and the exhaust system.
! It didn't stumble the second time. The engine screamed and the car lurched forward and accelerated with no smoke like it hadn't done since I rebuilt the engine! I stayed on it and the car just kept pulling stronger and stronger until I lifted! I did this a few more times and the car responded each time. I've owned this car for 11 years and it's never made such a great sound or accelerated as fast as today! I had the original Q-jet rebuilt when the motor was rebuilt ~3000 miles ago. During the rebuild I had the GM 350hp cam installed with flat top pistons, 2800 stall converter and a shift kit.What do you think happened? It's almost like there was something clogging the carb that got cleared out by flooring it. Through all this I've checked my fuel filter (it's clean) and changed the plugs and wires (the old plugs were still good). I'll keep driving it and see if my issues are finally behind me.
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From: Wellington, FL
St. Jude Donor '11 thru '25
I went out during lunch and did what you said. I drove it around for 20 minutes and when it was clear I floored it at 45mph. The transmission kicked down but the car stumbled again. I continued driving it a when traffic cleared again I floored it. Holy crap ! It didn't stumble the second time. The engine screamed and the car lurched forward and accelerated with no smoke like it hadn't done since I rebuilt the engine! I stayed on it and the car just kept pulling stronger and stronger until I lifted! I did this a few more times and the car responded each time. I've owned this car for 11 years and it's never made such a great sound or accelerated as fast as today! I had the original Q-jet rebuilt when the motor was rebuilt ~3000 miles ago. During the rebuild I had the GM 350hp cam installed with flat top pistons, 2800 stall converter and a shift kit.
What do you think happened? It's almost like there was something clogging the carb that got cleared out by flooring it. Through all this I've checked my fuel filter (it's clean) and changed the plugs and wires (the old plugs were still good). I'll keep driving it and see if my issues are finally behind me.
! It didn't stumble the second time. The engine screamed and the car lurched forward and accelerated with no smoke like it hadn't done since I rebuilt the engine! I stayed on it and the car just kept pulling stronger and stronger until I lifted! I did this a few more times and the car responded each time. I've owned this car for 11 years and it's never made such a great sound or accelerated as fast as today! I had the original Q-jet rebuilt when the motor was rebuilt ~3000 miles ago. During the rebuild I had the GM 350hp cam installed with flat top pistons, 2800 stall converter and a shift kit.What do you think happened? It's almost like there was something clogging the carb that got cleared out by flooring it. Through all this I've checked my fuel filter (it's clean) and changed the plugs and wires (the old plugs were still good). I'll keep driving it and see if my issues are finally behind me.
Good deal, John. I think your plugs were somewhat fouled and you cleaned them up. I've been thru this before with a '67 Vette I had. Another case I ran into was when I looked at a Vette to buy a while back. When first started, it ran like crap (all the time) and the seller didn't understand it. Anyway, I took it out and did what you did and when I brought it back, it ran great. Come to find out, he was backing this car in and out of his garage every day (never left the driveway) and never got warmed up. What this does is dump gas into the cylinders causing it to run much too rich and does a number on the plugs. As for your Vette, I would suspect the problem is those short trips to work. If you want to take it to work, my suggestion would be to run it at least a half hour, even if you have to go out of the way.
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From: Orlando FL
Good deal, John. I think your plugs were somewhat fouled and you cleaned them up. I've been thru this before with a '67 Vette I had. Another case I ran into was when I looked at a Vette to buy a while back. When first started, it ran like crap (all the time) and the seller didn't understand it. Anyway, I took it out and did what you did and when I brought it back, it ran great. Come to find out, he was backing this car in and out of his garage every day (never left the driveway) and never got warmed up. What this does is dump gas into the cylinders causing it to run much too rich and does a number on the plugs. As for your Vette, I would suspect the problem is those short trips to work. If you want to take it to work, my suggestion would be to run it at least a half hour, even if you have to go out of the way.