2150 Choke Confusion

[TenSeven]

1) Starting out with the engine cold and having not touched anything, should the choke plate be 'fully' closed?

2) If so, does the choke plate only open to the specified gap (1/8") only when you start the cold engine and the engine vacuum to the choke pull down kicks in?

3) Also, before starting, when you first 'load' the throttle to set the cam at its highest point, is the choke plate completely closed? Waiting for the engine vacuum to open it via the pull down?

Thanks

 

[Mark_88]

EDIT: OOOPS

There may be a handful of people that could answer these questions off the top of their heads...I'm not one of them...but I did find something that will help you if nobody else can answer...

Had to remove those answers...they do not apply to this carb...after a bit of reading I now realize I still don't know what I'm talking about even when I'm not actually talking about anything...I love being a not know it all...

http://grantorinosport.org/BubbaF250/carb/carb02a.html

 

[RonD]

On most mechanical Choke Carbs you need to press the throttle pedal down once, and release it, before starting the engine.
This does two things:
It sets the Choke closed based on temperature, more on that later.
And the carb's accelerator pump squirts some gas into the intake for starting.

Cold engines need extra fuel to run, that's the point of the Choke Plate and why it works, it restricts the air flow so more fuel is sucked from the Jets, cold engine needs to run Richer or it will stall.

When you accelerate, and Choke Plate is still partially closed, it will be pulled open by ported vacuum

On the side of the carb is a larger black plastic "cap", behind/under the "cap" is a temperature sensitive spring, a bi-metal spring, that is attached to the Choke Plate.
This cap can be adjusted on some models, it will have marks on it, for winter and summer.
You need more "Choke" in winter, and less in summer.
As the spring warms up the choke plate opens up, spring can be heated electrically or by exhaust manifold heat.
So there is no "correct gap" for the choke plate on a cold engine, it is solely based on the temperatures you will be having over the next few months, colder temps means smaller "gap" is needed.

In the good ol' days it was common to leave choke set for winter and then just put a wooden close pin on it during the summer months so it couldn't close all the way,

Vapor lock and chokes, those wooden cloths pins were invaluable.

Because there are no Jets, fuel injected engines can't use a Choke Plate, the computer runs in Choke Mode based on coolant temperature, uses ECT(engine coolant temp) sensor.
Computer runs richer fuel mix and higher idle in Choke mode

 

[Mark_88]

There is another way around a choke operation that I learned inadvertently....if you use a block heater it pretty much eliminates the need for a choke in cold weather...at least on the MC5200 carburetor.

After reading rons' post I now recall the step on older vehicles of pushing the pedal down to set the choke...since mine never worked I didn't have to do that but I remember my Dad doing that on cold mornings...

 

[TenSeven]

Thanks guys.

Electric choke, no hot air assist.

Sounds like, the choke plate starts off closed, you pump the accelerator pedal once to load the fast idle cam, the choke plate is still closed, start the engine, engine vacuum now engages the choke pull down opening the choke plate slightly. When you drive off, the cam goes to second position at the 'V' to slightly lower the fast idle. As the choke spring warms up it opens the choke plate to the point that the cam disenges for normal idle.

Close?

 

[RonD]

Yes, that reads like one of the designs used for automatic Chokes.

Although choke plate should stay open if engine is already warmed up, spring is warmed up.

Electric chokes had one failing, key on/engine off
If you were to turn on the key to listen to the Radio or got sidetracked, and didn't start the Cold engine.............
Choke spring would get heated up and open choke plate a bit, so when you did start the engine it would run rough until engine temp matched choke plate position.
So electric chokes are often powered by the alternator, so they don't start heating up the spring until engine is actually running.

 

[TenSeven]

Yes, that reads like one of the designs used for automatic Chokes.

Although choke plate should stay open if engine is already warmed up, spring is warmed up.

Electric chokes had one failing, key on/engine off
If you were to turn on the key to listen to the Radio or got sidetracked, and didn't start the Cold engine.............
Choke spring would get heated up and open choke plate a bit, so when you did start the engine it would run rough until engine temp matched choke plate position.
So electric chokes are often powered by the alternator, so they don't start heating up the spring until engine is actually running.

K, thanks Ron.

 

[TenSeven]

Pushed on the pedal, set the high idle, then adjusted the rpm's down to about 1200.

Let it start to warm up and hit the pedal again which brought the rpm's down to idle, which the engine did just fine.

After the engine was hot and had been idling for awhile I noticed the choke plate would only open not even half way to wide open vertical. I loosened the 3 screws on the choke cover and rotated it till the choke was now fully open. The only two marks on my choke cover are two hash marks spread apart about 1/3 the total circumference of the cover. There is a mark on the metal part of the carb/choke that the hash marks can line up to. When I rotated the choke cover the mark on the metal part lined up right between the two hash marks.

I'll see tomorrow when the engine is cold if the choke plate plate is fully closed again and if so, double check that the choke pull off is opening up the choke plate the correct distance.

 

[RonD]

Good work

Choke plate doesn't need to be fully closed in warmer weather, so don't readjust it if engine starts OK cold.

"Hot air rises", this means warmer air is Lighter than colder air.

Air: fuel ratio for gas engines is 14.7:1, this is a WEIGHT ratio
If you have 14.7 ounces of air you need to add 1 ounce of gasoline.
If you have 14.7 pounds of air you need to add 1 pound of gasoline.

And warmer air is Lighter so...........you need to add less fuel to get the correct mix, so less choke with warmer temps.
That is what the spring is for, as temps drop in the winter it will close choke plate more on start up.

You shouldn't have full choke in the summer, that's why we added a cloths pin to choke plate, lol, to keep it open more in the summer, then removed for the winter

 

[TenSeven]

Thanks Ron.

I understand the spring may not allow the choke plate to be fully closed, especially in warmer weather but, the choke plate 'should' eventually be wide open after the engine is hot and it's been running awhile, correct?

Since it only opened about half way, is turning the choke cap the proper way to adjust all the way open? (with the engine hot of coarse).

 

[RonD]

Thanks Ron.

I understand the spring may not allow the choke plate to be fully closed, especially in warmer weather but, the choke plate 'should' eventually be wide open after the engine is hot and it's been running awhile, correct?

Since it only opened about half way, is turning the choke cap the proper way to adjust all the way open? (with the engine hot of coarse).

Yes, that is the correct way to set the cap/spring.
Engine warmed up, turn cap until choke plate is fully open

 

[TenSeven]

Yes, that is the correct way to set the cap/spring.
Engine warmed up, turn cap until choke plate is fully open

Thanks.

Yesterday, while the engine was hot, I rotated the choke cap clockwise until the choke plate was full open. This morning, while the engine is cold I checked the choke plate. It has closed down but left about a 3/8" gap. It's not warm enough in the garage for the choke spring to be causing the plate to remain that far open.

 

[alwaysFlOoReD]

When its cold, hit the throttle to wide open and then let off all the way. If everything is set properly that plate will be in the closed position now.

Sent from my XT1032 using Tapatalk

 

[TenSeven]

When its cold, hit the throttle to wide open and then let off all the way. If everything is set properly that plate will be in the closed position now.

Sent from my XT1032 using Tapatalk

Thanks.

That's what I thought. If all is cold, engine, environment (my garage) and choke spring, then that choke plate should be fully shut, even after the pedal is pushed all the way down and let off. At that point it should be only the choke pull off that slightly opens the choke plate on startup.

So after letting the engine get hot the choke plate only opened about half way and when I checked when it was cold the choke plate wasn't fully closed.

I think I better start over.

 

[TenSeven]

I wonder if the other way to adjust the choke plate would be, when it's fully warmed up and the choke 'should' be wide open, if the choke isn't all the way open, would it work if you then loosened the three screws on the choke housing and rotated it until the choke wide open?

Also, the choke used to open all the way, however, starts were bad, Inhad to hold open the throttle to warm it up, the choke cam was not engaged. At that time the choke housing was oriented straight up and down. But in order for me to get the cam engaged I have to rotate the choke housing clockwise.

Edit: Checked just now, the engine is fully warmed up a pushed on the pedal released to cam to idle, however the choke is only 3/8" open, or halfway to fully open. The engine idles ok, but if I hold the choke open all the way the idle goes up a little and smooths out.