Sticking/Binding Choke Flap (1 Viewer)

[nachohouse]

Dealing with a sticking choke flap when I pull the choke cable. The choke knob moves free as well as the cable in the cable housing. There is a little slop in the mechanism, but doesn’t seem excessive.


When the choke is pulled, half of the time the choke flap will stick open. The other half of the time it will snap shut under the spring tension. When the flap does bind/stick, a quick poke with your finger will free it and snap it shut.


I lubed the pivot points of the flap, anything else I can try to get the mechanism to open and close smoother? Would be great to not have to remove the intake for cold starts.

Here’s a video:


2/1970 FJ40 with Aisan carb, rebuilt by Jim C 4ish years. PO deleted the choke breaker because of clearance issues with the brake booster. Thanks!

 

[65swb45]

Dealing with a sticking choke flap when I pull the choke cable. The choke knob moves free as well as the cable in the cable housing. There is a little slop in the mechanism, but doesn’t seem excessive.


When the choke is pulled, half of the time the choke flap will stick open. The other half of the time it will snap shut under the spring tension. When the flap does bind/stick, a quick poke with your finger will free it and snap it shut.


I lubed the pivot points of the flap, anything else I can try to get the mechanism to open and close smoother? Would be great to not have to remove the intake for cold starts.

Here’s a video:


2/1970 FJ40 with Aisan carb, rebuilt by Jim C 4ish years. PO deleted the choke breaker because of clearance issues with the brake booster. Thanks!

Two possibilities. One is that the butterfly is rubbing against the air horn, in which case you would be able to see faint arcs on the inside of the air horn where it is rubbing. Sometimes this can be adjusted by loosening the two brass set screws EVER SO SLIGHTLY and finding a way to wedge something in there that will move the flap from that spot ever so slightly.
The second possibility is that the shaft is bent or has a burr. Lubrication usually won’t fix that, and the shaft will need to be removed for proper evaluation. For that you will need to remove the air horn. Be prepared to replace the set screws for the butterfly. I don’t remember if they are 2.5mm or 3mm (I think they are the 2.5). Years ago @thebigredrocker turned me on to the fact that you can buy them from McMaster Carr.

 

[charliemeyer007]

Every few years I have to spray the down cable on my manual choke with WD-40 to it move freely. Mine is a wound wire with straight solid wire core. For plastic housing stuff a cable luber is the tool of choice. Flush the housing with like WD-40, then use the cable lube in the aerosol can with a pee tube Amazon.com : cable luber - https://www.amazon.com/cable-luber/s?k=cable+luber

The choke plate seems to move freely enough with your finger. I'd be looking at the trip mechanism(s) Spray that area good with carb spray - maybe there is some gunk build up inside the pivot points.

 

[nachohouse]

Two possibilities. One is that the butterfly is rubbing against the air horn, in which case you would be able to see faint arcs on the inside of the air horn where it is rubbing. Sometimes this can be adjusted by loosening the two brass set screws EVER SO SLIGHTLY and finding a way to wedge something in there that will move the flap from that spot ever so slightly.
The second possibility is that the shaft is bent or has a burr. Lubrication usually won’t fix that, and the shaft will need to be removed for proper evaluation. For that you will need to remove the air horn. Be prepared to replace the set screws for the butterfly. I don’t remember if they are 2.5mm or 3mm (I think they are the 2.5). Years ago @thebigredrocker turned me on to the fact that you can buy them from McMaster Carr.

Okay I do see some faint arcs on the airhorn. Loosen the screws, wedge something in, and then retighten?

What would happen I pull the top of the carb off and pass some fine grit sandpaper back and forth (and clean well obviously) along that side of the butterfly to clearance it a bit?

 

[nachohouse]

Removed the air horn and took it all apart today. Removing the butterfly from the shaft wasn’t as bad as I thought it would be. No burrs but the shaft does have a little more slop than I thought.

@65swb45 any chance you have a spare airhorn laying around with a tighter choke shaft? I’d even be interested in buying a whole rebuildable core to have as a spare if you’ve got one.

 

[65swb45]

Removed the air horn and took it all apart today. Removing the butterfly from the shaft wasn’t as bad as I thought it would be. No burrs but the shaft does have a little more slop than I thought.

@65swb45 any chance you have a spare airhorn laying around with a tighter choke shaft? I’d even be interested in buying a whole rebuildable core to have as a spare if you’ve got one.

There's a guy on Ebay who is selling an NOS choke shaft as part of a grouping of carb parts. From Cyprus. Maybe make him an offer for the lot, and I'll buy what you don't need.

 

[nachohouse]

Cool, I just offered, we’ll see what they say. Would all the wear be on the shaft or would the bore also have some wear?

 

[charliemeyer007]

A lot of times the worn hole can be reamed out and a bushing installed bringing it back to size.

 

[65swb45]

Cool, I just offered, we’ll see what they say. Would all the wear be on the shaft or would the bore also have some wear?

I think that, regardless, putting an NOS shaft in will cure your problem.

 

[mattressking]

Now that it is removed, partially reassemble. Wear in the choke shaft is minimal concern as it is above the primary butterfly so vacuum leaks aren't an 'issue'. If you look at your existing choke shaft, if there isn't notable wear on the two locations where it rotates in the carb lid, replacement is unnecessary. Since the carb housing is softer aluminum than steel, it's the housing that takes the 'beating'. I recommend you brass rifle brush, brake clean the bores and 0000 steel wool the shaft for your sanity.

Key item to note here, the butterfly needs to be assembled loosely with fresh brass screws (for your sanity) then rotate assembly open to close with both springs in their correct place. Many times the butterfly will be slightly bent or out of alignment causing the binding. Then slightly adjust the butterfly plate while rotating to find the sweet spot. When setup correctly, it will open and close smoothly under spring tension.