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The pictures below are from my '72 I bought last summer. The choke is very slow to open. The first picture shows the choke linkage rod position when the motor is cold. I removed it from the choke linkage so you can see it's position when cold. The choke plate is completely closed. The second picture shows the plate that the choke coil bolts to. The intake is an Edelbrock performer. The car does not have an exhaust heat riser.
What can I do to allow the choke to open faster? On a 75 degree day the choke takes more than 10 minutes to open.
Thanks in advance for any suggestions.
Position of linkage rod when cold. Choke butterfly is closed Plate under choke coil
Not sure on your setup when cold whether the coil is pulling down or pushing up. If pushing up try bending the choke rod to shorten it so it has less tension when completely closed. If pulling down make a longer rod.
Not sure on your setup when cold whether the coil is pulling down or pushing up. If pushing up try bending the choke rod to shorten it so it has less tension when completely closed. If pulling down make a longer rod.
When cold the coil is pulling down. As the engine warms up the coil will push the linkage up and open the choke.
You also need to set the choke properly when cold. The upper air valve in the carb should never be completely closed when the choke is set (do not push pedal to floor; just tap it to get the choke mechanism to close). The Chevrolet Chassis Service Manual for your model year has detailed instructions on how the choke is adjusted properly. It is in the FUEL Section on carburetor details. Adjust the carb features correctly and you should have no problems.
I believe that your primary issue is that the tension in the divorced-choke spring is set much to high. This would close the airvalve completely when cold and also require a much longer time to fully open.
You also need to set the choke properly when cold. The upper air valve in the carb should never be completely closed when the choke is set (do not push pedal to floor; just tap it to get the choke mechanism to close). The Chevrolet Chassis Service Manual for your model year has detailed instructions on how the choke is adjusted properly. It is in the FUEL Section on carburetor details. Adjust the carb features correctly and you should have no problems.
I believe that your primary issue is that the tension in the divorced-choke spring is set much to high. This would close the airvalve completely when cold and also require a much longer time to fully open.
Is there anything I can do to reduce the spring tension?
I noticed the new intake gaskets and aftermarket bolts. When the gaskets were installed did you use the small metal block off or restrictor plates in the exhaust cross-over passages? They always come with the gaskets and should NOT be used with a divorced choke. You need the hot exhaust going through the intake for that choke. Also, is the exhaust heat riser valve just below the right side exhaust manifold still there and working properly to divert exhaust through the intake manifold when cold?
Either one will cause your problem.
Last edited by CanadaGrant; Jan 24, 2019 at 03:01 PM.
I noticed the new intake gaskets and aftermarket bolts. When the gaskets were installed did you use the small metal block off or restrictor plates in the exhaust cross-over passages? They always come with the gaskets and should NOT be used with a divorced choke. You need the hot exhaust going through the intake for that choke. Also, is the exhaust heat riser valve just below the right side exhaust manifold still there and working properly to divert exhaust through the intake manifold when cold?
Either one will cause your problem.
The engine was rebuilt before I bought the car. Therefore, I don't know what the builder did relative to the gaskets. Also, no heat riser exists. It appears that when the new exhaust was installed before I bought the car they didn't reinstall the heat riser.
Mike's Carburetor Parts sells an electric choke that installs in place of the current choke coil assembly. It is adjustable and has a thermostat to detect engine temp. Perhaps I should look into one of these.
The engine was rebuilt before I bought the car. Therefore, I don't know what the builder did relative to the gaskets. Also, no heat riser exists. It appears that when the new exhaust was installed before I bought the car they didn't reinstall the heat riser.
Mike's Carburetor Parts sells an electric choke that installs in place of the current choke coil assembly. It is adjustable and has a thermostat to detect engine temp. Perhaps I should look into one of these.
Thanks for your help.
I recommend the electric choke conversion.......easy to do.
Yes, you need the heat riser to restrict exhaust flow which diverts it through the intake to the left side until the riser warms up. I would be willing to bet that the restrictor plates were also installed with the intake gaskets but you need both the heat riser and open ports through the intake to make it work. Your easiest bet if you don't want to replace the riser and remove the restrictors if installed would be electric. For a power supply I have sometimes used the yellow wire going to the wiper motor plug. Three wires. Blue, green and yellow. The center yellow wire is live whenever the ignition is in the ON position and is fused.
From: At my Bar drinking and wrenching in Lafayette Colorado
Remove the mounting plate for the divorced choke. With the plate removed, you should be able to look inside the exhaust crossover to see if the manifold was installed with a crossover blockoff gasket or a crossover restrictor plate in the gasket. If the gasket does not have a wide open crossover hole with no restriction, your choke will not work right. I'll bet that gasket is either blocked or restricted, and you need to replace it. This, of course, assumes that you have correctly adjusted the choke rod - if it is not adjusted correctly, the "choke-on" duration will not be right.
Remove the mounting plate for the divorced choke. With the plate removed, you should be able to look inside the exhaust crossover to see if the manifold was installed with a crossover blockoff gasket or a crossover restrictor plate in the gasket. If the gasket does not have a wide open crossover hole with no restriction, your choke will not work right. I'll bet that gasket is either blocked or restricted, and you need to replace it. This, of course, assumes that you have correctly adjusted the choke rod - if it is not adjusted correctly, the "choke-on" duration will not be right.
Lars
Here is a picture of the intake with the plate removed.
The blocking plate will be right at the gasket. You can stick your little finger down there and feel it. It's too clean in the pic for it to be open or it would look like the inside of your tailpipe. If your not worried about originality, go with the electric choke. Otherwise replace the intake gaskets and install a heat riser. Heating up the intake, especially aluminum, with hot exhaust gasses was one of the dumber ideas from GM. Below is the original aluminum Winters intake off my 69 427. That's what happens when you shock cast aluminum like that too many times. It was so brittle in the cross over area it would shatter like glass if you tapped it. You want to keep the intake as cool as possible and hot exhaust to run a choke is a really bad idea. There is normally a tin heat shield over the bottom of this intake held on by 4 blind rivets. I didn't even see the crack and only found it when I shone a light in the passage to check it and saw the light reflection off the under side of the shield....
Last edited by CanadaGrant; Jan 25, 2019 at 12:25 AM.
'72 350 - Slow Opening Divorced Choke
The blocking plate will be right at the gasket. You can stick your little finger down there and feel it. It's too clean in the pic for it to be open or it would look like the inside of your tailpipe. If your not worried about originality, go with the electric choke. Otherwise replace the intake gaskets and install a heat riser. Heating up the intake, especially aluminum, with hot exhaust gasses was one of the dumber ideas from GM. Below is the original aluminum Winters intake off my 69 427. That's what happens when you shock cast aluminum like that too many times. It was so brittle in the cross over area it would shatter like glass if you tapped it. You want to keep the intake as cool as possible and hot exhaust to run a choke is a really bad idea. There is normally a tin heat shield over the bottom of this intake held on by 4 blind rivets. I didn't even see the crack and only found it when I shone a light in the passage to check it and saw the light reflection off the under side of the shield....
