Cold start choke question

[Peer81]

From the beginning my carb has this thing, after rebuilding everything I thought I would find what was the problem but no the fenomenon is still there.

What is the "problem"?
When I start the engine the choke is on the second step (why not the highest step?). But no problem there, idling a little ruff but no big problem. After 2 to 5 minutes the rpm goes up from 300 to 400 rpm! Idling nicer without any problem. I was working on the carb today to get the choke rpm up so I could see everything when this happend.
The carb didn't change anything, I always thought the choke would go to the highest step but that is not true. The choke itself didn't open or close more then before or after.
As the coolant temp is about 100F by then I would think that is still to cold for the ECM to kick in but as I have a heated O2 sensor, the o2 sensor would be operating by then.

So who also has this fenomenon? And has it something to do with the ECM?

Greetings Peter

 

[Tommy Almond]

Peter I had my original ECM controlled Q-jet re-manfactured by Mid American Carbs in Florida and it works perfect. Cold start I just pop the gas twice she fires up and idles 700'ish for a couple of minutes and then revs up to about 1800rpm until either it knocks down on it own or I hit the gas and knock the choke off.
On the rebuilt carb I had on before I had to spin th engine over several times first, then hit the gas twice for chock to set and then spin the crank and the engine would rev up higher higher quicker and not knock off just by hitting the gas.
You may have a linkage not bend just right or the cam or level may be sticking some on another part. You should still be able to turn your outside plate on the spring cover to set the chock plate to close more even if just on the 2nd step.
I don't believe the ECM has anything to do with the chock release but would be sending a richer mixture to the carb during warmup until desired temps are reached.

 

[Wajulia]

I am not an expert on choke operation, but I will share what I know -- First, the ECM has no control over the choke at all.

1) the choke goes to the high idle step by depressing the gas pedal all the way. When you depress the pedal all the way, see what part of the linkage is not allowing it to go to the high idle step, Perhaps one the linkages need to be tweeked.

2) The only thing you will see while the car warms up is the choke butterfly open. Nothing else happens until you blip the gas. Does the butterfly open as the car warms up? If no -- check linkages and voltage to the choke.

Good luck

 

[Vettehead Mikey]

I am not an expert on choke operation, but I will share what I know -- First, the ECM has no control over the choke at all.

1) the choke goes to the high idle step by depressing the gas pedal all the way. When you depress the pedal all the way, see what part of the linkage is not allowing it to go to the high idle step, Perhaps one the linkages need to be tweeked.

2) The only thing you will see while the car warms up is the choke butterfly open. Nothing else happens until you blip the gas. Does the butterfly open as the car warms up? If no -- check linkages and voltage to the choke.

Good luck

Agreed.

 

[TimAT]

Set the choke by pressing the gas pedal to the floor. One time sets the choke, but most guys hit it a couple of times. Crank, and as soon as it starts the choke pull off opens the choke slightly. I recall it's like 7* open, but that may be my old memory. As it warms up, the choke thermostat pulls the choke plate open more, but still won't open fully until the engine is warmed up. THe fast idle will stay on until the gas pedal is slightly pressed.

 

[Peer81]

Thanks but here it what I think.

First no need to depress the pedal to the floor. I think 1/4 or maybe 1/2 is good enough to get the choke to the highest step. But is the choke spring getting the choke to the highest step?
What I do on a cold start is slightly push to pedal to close the choke valve (and setting the choke to the middel or highest step) after that just start it right away and then push the pedal a little to give it some extra fuel. If you need to pump the pedal I think your cold start choke valve opening is wrong (to much opening).
No problem with my choke valve it works perfect, are set by Lars his paper and adjusted to a more perfect cold start mixture.
So that is not where the "problem" is.
If I'm looking at the choke valve, its not moving, and from one second to the next rpm goes up 300 without anything changing I think its something else or not?
Maybe time to reinstall my A/F ratio meter to see what happens.

Greetings Peter

 

[Vettehead Mikey]

The purpose of pushing the pedal all the way to the floor is to give a large shot of fuel from the accelerator pump.