Manual choke question

dcdoug · #1 (**permalink**) 12-15-2009, 02:42 PM

I have a manual choke on my FE (750 Holley with S&H air cleaner). I find that when it is 30 degrees or less out, using the choke helps the engine fire initially, but after the engine starts it idles better when I push the choke back in right away. I probably feather the throttle for the first 20 seconds or so and then just let it idle to warm up, but it doesn't idle as well in either case with the choke engaged at all.

Why is this? Is it because the choke helps on start-up due to the dense cold air, but then due to the horn/air cleaner air flow/clearance issues that it just can't get enough air to idle properly with the choke engaged, even partially, especially if I am still feathering the throttle?

I wonder if there is something I can do to take more advantage of the choke in really cold weather. Otherwise I may just remove it altogether (and then evaluate whether to mill off the horn when I am next at the dyno).

Thoughts?

WarrenG · #2 (**permalink**) 12-15-2009, 03:16 PM

Quote:

Originally Posted by dcdoug

I have a manual choke on my FE (750 Holley with S&H air cleaner). I find that when it is 30 degrees or less out, using the choke helps the engine fire initially, but after the engine starts it idles better when I push the choke back in right away. I probably feather the throttle for the first 20 seconds or so and then just let it idle to warm up, but it doesn't idle as well in either case with the choke engaged at all.

Why is this? Is it because the choke helps on start-up due to the dense cold air, but then due to the horn/air cleaner air flow/clearance issues that it just can't get enough air to idle properly with the choke engaged, even partially, especially if I am still feathering the throttle?

I wonder if there is something I can do to take more advantage of the choke in really cold weather. Otherwise I may just remove it altogether (and then evaluate whether to mill off the horn when I am next at the dyno).

Thoughts?

That's exactly what happens when I use the manual choke on my Lawn Tractor and Lawn Mower!

dcdoug · #3 (**permalink**) 12-15-2009, 03:21 PM

Quote:

Originally Posted by WarrenG

That's exactly what happens when I use the manual choke on my Lawn Tractor and Lawn Mower!

You mow your lawn when it is 30 out? You must have some kind of super grass that grows all winter long.

cdnus · #4 (**permalink**) 12-15-2009, 04:00 PM

Doug
With a manual choke you should depress the throttle 1/4 then pull the choke on while the peddle is depressed, then release the peddle. This will engage the fast idle cam allowing the engine to fast idle once started, (do not touch the peddle once the choke is engaged) when it starts you can slowly push the choke in as required to keep the engine running clean.
If the engine will not fast idle once started you may have to adjust the screw for that on the fast idle cam to increase the speed.
Once the engine is warmed up & can idle on its own push the choke all the way in & tap the gas peddle to release the fast idle cam.
You should be good to go.
You will soon learn the small differences required for your car, but this is the general method used.

Craig

1ntCobra · #5 (**permalink**) 12-15-2009, 04:38 PM

Quote:

Originally Posted by dcdoug

You mow your lawn when it is 30 out? You must have some kind of super grass that grows all winter long.

I mulch my leaves with my tractor and usually have leaves still falling off a few stubborn trees after Thanksgiving. There was one year that I procrastinated and finished mulching my leaves after Christmas...

dcdoug · #6 (**permalink**) 12-15-2009, 08:07 PM

Quote:

Originally Posted by cdnus

Doug
With a manual choke you should depress the throttle 1/4 then pull the choke on while the peddle is depressed, then release the peddle. This will engage the fast idle cam allowing the engine to fast idle once started, (do not touch the peddle once the choke is engaged) when it starts you can slowly push the choke in as required to keep the engine running clean.
If the engine will not fast idle once started you may have to adjust the screw for that on the fast idle cam to increase the speed.
Once the engine is warmed up & can idle on its own push the choke all the way in & tap the gas peddle to release the fast idle cam.
You should be good to go.
You will soon learn the small differences required for your car, but this is the general method used.

Craig

Thanks, will give that a try.

*13* · #7 (**permalink**) 12-15-2009, 08:50 PM

Also, are you adjusting the choke so it is slightly open? & are your running manual or vacuum secondaries? If vacuum, are they closed completely at idle?the motor needs an enriched mixture when cold, not a complete choking. If you close the choke completely you shut off all air. Likewise, if your secondary butterflies were pulling open, which is doubtfull, you may be letting too much air in. This is where an Electric Choke is nice. You pump the pedal slightly to engage the Cam & start the engine. The electric choke, if adjusted properly, slowly starts to open. By the time Its open all the way your motor should be idling properly, with the fast idle cam disengaged.

patrickt · #8 (**permalink**) 12-16-2009, 05:29 AM

Just pull the damn thing off. You don't need it and you're just going to end up fouling your plugs and then wondering why your car isn't running right.

Bill Bess · #9 (**permalink**) 12-16-2009, 06:05 AM

I agree with Patrick...take the damm thing off. In my entire life I never had a engine run right for very long with an automatic or maunal choke. If set up properly, they will work as designed, but you must know how to let them do their thing..don't keep pumping the pedal after it starts.
In 30 degree weather mine with no choke works great...starts right up....feather the throttle a bit until it idles and warms up ( about 2 -3 minutes).

Ron61 · #10 (**permalink**) 12-16-2009, 06:22 AM

I didn't have a choke on my Cobra and it started right up and ran fine even in cold weather, but we don't have the low temperatures like back East. My other car has an electric choke which I disconnected many years ago but left the assembly on as I use the terminals for a tie point to get juice to some other places. It sets for months at a time and all I have to do is mash the gas pedal about 3 times, wait a second or two for the fuel to get down into the chambers and it starts right up. Then I have to hold the pedal down just a little for the first minute and it is good after that.

Ron

dcdoug · #11 (**permalink**) 12-16-2009, 07:43 AM

Quote:

Originally Posted by *13*

Also, are you adjusting the choke so it is slightly open? & are your running manual or vacuum secondaries? If vacuum, are they closed completely at idle?the motor needs an enriched mixture when cold, not a complete choking. If you close the choke completely you shut off all air. Likewise, if your secondary butterflies were pulling open, which is doubtfull, you may be letting too much air in. This is where an Electric Choke is nice. You pump the pedal slightly to engage the Cam & start the engine. The electric choke, if adjusted properly, slowly starts to open. By the time Its open all the way your motor should be idling properly, with the fast idle cam disengaged.

Its not fully closed, just partially. Was still playing around with the right amount. I have vacuum secondaries and assume they are closed, but haven't verified.

dcdoug · #12 (**permalink**) 12-16-2009, 07:48 AM

Quote:

Originally Posted by Bill Bess

I agree with Patrick...take the damm thing off. In my entire life I never had a engine run right for very long with an automatic or maunal choke. If set up properly, they will work as designed, but you must know how to let them do their thing..don't keep pumping the pedal after it starts.
In 30 degree weather mine with no choke works great...starts right up....feather the throttle a bit until it idles and warms up ( about 2 -3 minutes).

I sort of regret going with a choke at all and may pull it off. It starts easier than I thought it would when really cold without using the choke and I don't mind feathering it for about 20 seconds and then letting it idle for a bit, so I'm not seeing much benefit. But I will probably still play around with it a bit more before I make the decision.

Silverback51 · #13 (**permalink**) 12-16-2009, 08:39 AM

Last time I started mine it was 41 degrees out and the car had sat for 5 or 6 weeks. No chokes on either carb. I just lightly pump the throttle as I turn it over until it starts and then feather the throttle for about a minute until it's running smooth.

I agree, dump the choke.

mdross1 · #14 (**permalink**) 12-18-2009, 06:28 AM

Sounds to me like you have a rich idle mixture to not need the choke after startup.You can try starting your motor without the choke to see if you would like it removed. My 850 dbl pump on a 460ci needs choke to start, then feather it back a little to stay idling.

dcdoug · #15 (**permalink**) 12-18-2009, 07:25 AM

Quote:

Originally Posted by mdross1

Sounds to me like you have a rich idle mixture to not need the choke after startup.You can try starting your motor without the choke to see if you would like it removed. My 850 dbl pump on a 460ci needs choke to start, then feather it back a little to stay idling.

I may very well have a bit of a rich mixture at idle and will take a look at that.