MALIBU¬†Cold ūü•∂ Start

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ck80

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Thanks. That sounds about it.
To some degree you are always going to have that issue you complain of , or, you're going to be too rich the rest of the time and risk dieseling, high idle, poor fuel mileage, and the associated conditions.

Reason: the carb is set and forget. It isn't dynamic with constant changes of richening and leaning out the fuel mixture based on measurements being taken like FI. To alter the mixture you need to adjust the screws.

When an engine is cold, some of the fuel being injected in the manifolds, passages, and such will condense onto the internal surfaces, effectively leaning out the A/F ratio. That's why it acts chugging, it's running lean, and, it's why giving a little gas pedal helps warm it up quicker with it running smoother while you do it for the 30 or 60 seconds. FI motors measure the A/F ratio, see its lean, and increase the amount of fuel injectors dump to raise the A/F mixture so you don't get that chugging/rough idle. Carbs don't do this. BUT, if you tune your carb to dump extra fuel so that it can have some condense when things get cold, its going to run rich the rest of the time.

GM experimented with some things to attempt to change this for carbs just before switching to FI in the form of their E.F.E. heater element baseplates between the carbs and intake manifolds in some motors, but, the metal grids the air/fuel mixture would pass though in those E.F.E. plates to be heated enough that ideally less fuel would condense prior to ignition on cold starts invariably melted over time. Seen plenty that were partially intact on disassembled motors.

So. If it works properly with good ignition patterns on the plugs and no issues when it is temperate out you need to make a choice:
1) leave it alone and deal with the normal warm up periods expected for carbed vehicles in cold weather
2) keep a notebook with set 'tune' adjustments for certain temperature ranges and keep adjusting your carb screws back and forth based on upcoming weather, a warm.amd a cold setting should suffice for Boston
3) set it to be rich when it's warm, but have less lean symptoms cold, and take the risks of damaging the cats with unburnt fuel, and all those other problems with potentially getting too rich mentioned above- dieseling, etc, etc. Maybe find a fine line where you sacrifice fuel economy and need to clean plugs and such more often, but, aren't quite as cold impacted. Sort of doesn't run quite as well or clean in warm weather, but, needs less warm up in the cold.
 
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Dezimade

Greasemonkey
Sep 22, 2021
120
17
18
Boston Ma.
To some degree you are always going to have that issue you complain of , or, you're going to be too rich the rest of the time and risk dieseling, high idle, poor fuel mileage, and the associated conditions.

Reason: the carb is set and forget. It isn't dynamic with constant changes of richening and leaning out the fuel mixture based on measurements being taken like FI. To alter the mixture you need to adjust the screws.

When an engine is cold, some of the fuel being injected in the manifolds, passages, and such will condense onto the internal surfaces, effectively leaning out the A/F ratio. That's why it acts chugging, it's running lean, and, it's why giving a little gas pedal helps warm it up quicker with it running smoother while you do it for the 30 or 60 seconds. FI motors measure the A/F ratio, see its lean, and increase the amount of fuel injectors dump to raise the A/F mixture so you don't get that chugging/rough idle. Carbs don't do this. BUT, if you tune your carb to dump extra fuel so that it can have some condense when things get cold, its going to run rich the rest of the time.

GM experimented with some things to attempt to change this for carbs just before switching to FI in the form of their E.F.E. heater element baseplates between the carbs and intake manifolds in some motors, but, the metal grids the air/fuel mixture would pass though in those E.F.E. plates to be heated enough that ideally less fuel would condense prior to ignition on cold starts invariably melted over time. Seen plenty that were partially intact on disassembled motors.

So. If it works properly with good ignition patterns on the plugs and no issues when it is temperate out you need to make a choice:
1) leave it alone and deal with the normal warm up periods expected for carbed vehicles in cold weather
2) keep a notebook with set 'tune' adjustments for certain temperature ranges and keep adjusting your carb screws back and forth based on upcoming weather, a warm.amd a cold setting should suffice for Boston
3) set it to be rich when it's warm, but have less lean symptoms cold, and take the risks of damaging the cats with unburnt fuel, and all those other problems with potentially getting too rich mentioned above- dieseling, etc, etc. Maybe find a fine line where you sacrifice fuel economy and need to clean plugs and such more often, but, aren't quite as cold impacted. Sort of doesn't run quite as well or clean in warm weather, but, needs less warm up in the cold.
Great information. I thank you sir !!
 

Dezimade

Greasemonkey
Sep 22, 2021
120
17
18
Boston Ma.

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ck80

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Great information. I thank you sir !!
Very welcome.

I'm not trying to say there's zero room to tweak things a little, or that nothing on a 40 year old motor is worn. It is possible.

But at the same time, that behavior doesn't necessarily mean something is broken the way it might if you were in say a 2002 firebird.

What I am trying to do is just let you know why the cars are prone to doing it, and then you can just proceed with a better understanding of the antiquated systems you're dealing with.
 
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Dezimade

Greasemonkey
Sep 22, 2021
120
17
18
Boston Ma.
Very welcome.

I'm not trying to say there's zero room to tweak things a little, or that nothing on a 40 year old motor is worn. It is possible.

But at the same time, that behavior doesn't necessarily mean something is broken the way it might if you were in say a 2002 firebird.

What I am trying to do is just let you know why the cars are prone to doing it, and then you can just proceed with a better understanding of the antiquated systems you're dealing with.
I respect anyone with the time to explain experience. Thanks
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
Do you have the Thermac aircleaner hooked up?
 
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ck80

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Do you have the Thermac aircleaner hooked up?
Looking back, he had a single pic above that looks like a modified or aftermarket air cleaner posted above. The neck is short and smooth, doesn't show the normal bump for the thermostatic vacuum unit on the snorkle, nor does it show a heat stove pipe glinting underneath.

Dezimade -
Basic pieces would be a heat stove on the snorkle side exhaust manifold - basically a shaped piece of tin work with a circular opening on the top; the pipe which by gbody years was usually alexible alum tube with a clamp on either end connecting the heat stove to the snorkle, then on the air cleaner snorkle you had a temp senor and some vacuum lines, looked like a small round puck on the air cleaner snorkle. Inside the snorkle neck you had a metal flapper. It was the job of the sensor to adjust the door so below mid 80s *F air charge temp the door closed off so air only came from the stove to carb. Then in the lower 100s it opened partway to blend the air, finally in the 130s or 40s air charge temp it would open to pull air from the end of the snorkle tube and close off the heat stove source.

Different models had different locations for some of the stuff, but, in the gbody era that was generally the set up.
 
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Dezimade

Greasemonkey
Sep 22, 2021
120
17
18
Boston Ma.
Looking back, he had a single pic above that looks like a modified or aftermarket air cleaner posted above. The neck is short and smooth, doesn't show the normal bump for the thermostatic vacuum unit on the snorkle, nor does it show a heat stove pipe glinting underneath.

Dezimade -
Basic pieces would be a heat stove on the snorkle side exhaust manifold - basically a shaped piece of tin work with a circular opening on the top; the pipe which by gbody years was usually alexible alum tube with a clamp on either end connecting the heat stove to the snorkle, then on the air cleaner snorkle you had a temp senor and some vacuum lines, looked like a small round puck on the air cleaner snorkle. Inside the snorkle neck you had a metal flapper. It was the job of the sensor to adjust the door so below mid 80s *F air charge temp the door closed off so air only came from the stove to carb. Then in the lower 100s it opened partway to blend the air, finally in the 130s or 40s air charge temp it would open to pull air from the end of the snorkle tube and close off the heat stove source.

Different models had different locations for some of the stuff, but, in the gbody era that was generally the set up.
Super interesting. I will try my best to grasp this valuable information thanks man.
 
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