Are carburetors supposed to do this?

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Glam_Stachee

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In my 1991 Peugeot 309 when it's colder outside, no matter the engine temperature, when I'm driving on low revs for a while and then add a more "generous amount" of gas the engine just stops responding and then suddenly springs forward violently. Only happens when I'm in 1st gear and rarely 2nd. The engine doesn't stall but I theorize I just overflow the carburetor with fuel. It's a twin-barrel Solex carb, probably factory, just had it adjusted. Strangely I never had this happen on my older cars with Webers, though I know Solex is also owned by Weber.
 
Sounds like an initial lean condition. Have you checked the function of the accelerator pump?
 
On this solex carb, simply check the accel pump by watching the small yellow tube inside the bore squirt fuel while depressing accel command. If it squirts correctly, check adjustment according service manual for your very carb number. Then, check the sealing and flow of the vacuum line going from the carb to the ignition distributor cap.
 
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It's underfueling. Not overfueling it. When it's cold it needs more gas to run. A stumble like you explain is usually an acellerator pump problem. It's also one of the reasons why fuel injection is better.
 
When the throttle plate is suddenly opened further, air rushes in faster than fuel; this creates a temporary lean condition. Carburetors will use an accelerator pump to correct this temporary lean condition by squirting fuel directly into the Venturi.
 
Originally Posted by Superflan
On this solex carb, simply check the accel pump by watching the small yellow tube inside the bore squirt fuel while depressing accel command. If it squirts correctly, check adjustment according service manual for your very carb number. Then, check the sealing and flow of the vacuum line going from the carb to the ignition distributor cap.
The second thing I already did, all the vacuum lines are tip top, but do you know where I could find the proper adjustment? I checked my own service manual that came with the car and I checked the Haynes manual, couldn't find any info on carb adjustment.
Originally Posted by Chris142
It's underfueling. Not overfueling it. When it's cold it needs more gas to run. A stumble like you explain is usually an acellerator pump problem. It's also one of the reasons why fuel injection is better.
First of: Carburetor>>>Fuel injection. Also I guess you are right, my car has a manual choke and I have a bad habit of always releasing it a bit prematurely, and the car starts idling very stuttery. The question is should I keep a little bit of choke when it's freezing cold because it seems to idle a lot better, or would that just carbon up the engine?
 
Originally Posted by das_peikko
When the throttle plate is suddenly opened further, air rushes in faster than fuel; this creates a temporary lean condition. Carburetors will use an accelerator pump to correct this temporary lean condition by squirting fuel directly into the Venturi.
Thanks, this has been the most helpful explanation of this I've heard so far.
 
The choke should stay on as long as needed for the vehicle to idle correctly. A fall in idle is ok with the choke off, but it shouldn't stumble. If it does it still needs to be on to some degree or the mixture isn't set right. Unless it's super cold outside the choke shouldn't need to be on more than a couple minutes before you can start dialing it back or turn it off completely. My Austin-Mini I had that I would start over the winter, I would start with full choke. Wait a minute then start dialing it back really slowly until the first sign I would feel the engine slightly studder a bit and the just increase it a bit from that point and wait longer and try dialing it back again. Usually the whole process took about 2-3 minutes in approximately 0c (32F) temperatures with just fast cold idle. It's better for the engine doing this than letting it ride full choke right until it's fully warm as this encourage a much richer mixture and will put a lot of fuel into the oil and wash the cylinders walls of its oil film creating more engine wear as well as contribute to carbon build-up in the engine. It's better to keep it on the lean side of the choke as much as possible as it's warming up. Listen and feel what the engine says as you start reducing the amount of choke and inch it along from there. Also in regards to mixture when setting it, warm up the vehicle fully and then turn the mixture screw to lean out the idle jet until there is a reduction in engine rpm slightly (like ~50rpm) and then turn back toward the rich side just slightly from there. This will encourage as lean of a mixture as possible but keep it as close to the proper mixture as possible. Usually about 1/2 turn from the lean stumble point on most carbs. The best way is to set it up using a 5 gas analyzer looking at the emissions like CO at idle but most folks don't have these. (Make sure your spark timing is correct before you do this)
 
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The manual choke is pushed in gradually as the engine warms up. It takes some experience to "get a feel" for how much is too much/too little
 
Originally Posted by StevieC
The choke should stay on as long as needed for the vehicle to idle correctly. A fall in idle is ok with the choke off, but it shouldn't stumble. If it does it still needs to be on to some degree or the mixture isn't set right. Unless it's super cold outside the choke shouldn't need to be on more than a couple minutes before you can start dialing it back or turn it off completely. My Austin-Mini I had that I would start over the winter, I would start with full choke. Wait a minute then start dialing it back really slowly until the first sign I would feel the engine slightly studder a bit and the just increase it a bit from that point and wait longer and try dialing it back again. Usually the whole process took about 2-3 minutes in approximately 0c (32F) temperatures with just fast cold idle. It's better for the engine doing this than letting it ride full choke right until it's fully warm as this encourage a much richer mixture and will put a lot of fuel into the oil and wash the cylinders walls of its oil film creating more engine wear as well as contribute to carbon build-up in the engine. It's better to keep it on the lean side of the choke as much as possible as it's warming up. Listen and feel what the engine says as you start reducing the amount of choke and inch it along from there. Also in regards to mixture when setting it, warm up the vehicle fully and then turn the mixture screw to lean out the idle jet until there is a reduction in engine rpm slightly (like ~50rpm) and then turn back toward the rich side just slightly from there. This will encourage as lean of a mixture as possible but keep it as close to the proper mixture as possible. Usually about 1/2 turn from the lean stumble point on most carbs. The best way is to set it up using a 5 gas analyzer looking at the emissions like CO at idle but most folks don't have these. (Make sure your spark timing is correct before you do this)
Nah the carb is tuned properly, it ran horribly lean when I got it, so that was the first thing I addressed once I got the car home. I've had other cars and they all had manual chokes, however this Peugeot is new to me because it has a fast idle when you pull the choke, which my previous cars didn't. Also your Mini is real quick with warming up, I clocked mine and it takes about 5 minutes to heat up before it starts working without the choke at about 10c, though it only takes about 1 minute when it's quite warm outside. Also yeah I do the same thing, pull the choke all the way, start the car, then put it to half-way and from there I slowly dial it down as I see the temperature gauge raise
 
"First of: Carburetor>>>Fuel injection." But you are the one with the problem. I would bet that a survey would reveal that 95% or more would prefer fuel injection over a carburetor. But to each his own.
 
Originally Posted by Glam_Stachee
Originally Posted by Chris142
It's also one of the reasons why fuel injection is better.
First off: Carburetor>>>Fuel injection.
Where have you been for the last 30 years?......Under a rock?
 
Originally Posted by Glam_Stachee
Nah the carb is tuned properly, it ran horribly lean when I got it, so that was the first thing I addressed once I got the car home. I've had other cars and they all had manual chokes, however this Peugeot is new to me because it has a fast idle when you pull the choke, which my previous cars didn't. Also your Mini is real quick with warming up, I clocked mine and it takes about 5 minutes to heat up before it starts working without the choke at about 10c, though it only takes about 1 minute when it's quite warm outside. Also yeah I do the same thing, pull the choke all the way, start the car, then put it to half-way and from there I slowly dial it down as I see the temperature gauge raise
Sounds good, just thought I would put it out there in case it was anything else... Sounds like you have it all within check.
 
Originally Posted by clinebarger
Originally Posted by Glam_Stachee
Originally Posted by Chris142
It's also one of the reasons why fuel injection is better.
First off: Carburetor>>>Fuel injection.
Where have you been for the last 30 years?......Under a rock?
Actually in the driver's seat of a carbureted car, besides, I want to see your fancy fuel injection start right up after sitting for 2 years outside.
 
Originally Posted by Glam_Stachee
Originally Posted by clinebarger
Originally Posted by Glam_Stachee
Originally Posted by Chris142
It's also one of the reasons why fuel injection is better.
First off: Carburetor>>>Fuel injection.
Where have you been for the last 30 years?......Under a rock?
Actually in the driver's seat of a carbureted car, besides, I want to see your fancy fuel injection start right up after sitting for 2 years outside.
Um.....Okay.
 
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Originally Posted by Glam_Stachee
Actually in the driver's seat of a carbureted car, besides, I want to see your fancy fuel injection start right up after sitting for 2 years outside.
And after two years sitting unused outside, what carb isn't going to need to be cleaned internally within an inch of its life and rebuilt, at the very least? I am glad that carbs have been relegated, for the most part, to history. I haven't had a carb on any truck, OPE, snowmobile, or motorcycle in the last 30 plus years that didn't need a considerable amount of babysitting just to "work."
 
Why did an honest question about a carburetor problem turn into a carburetor-vs.-fuel-injection argument?? As if, the OP has a choice on which to use in his car. A well-maintained carburetor (high-quality gas, properly installed air filter, no tampering or abuse) will last virtually forever, save perhaps some torn vacuum diaphragm that may need replacing. I did carefully rebuild mine myself ten years ago but it was running OK before then despite the abuse in its earlier life.
 
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