What closes the primarys on a 65 TBird with a 4100 remanufactured Autolite carb

[makrie]

I just purchased a 65 TBird. It came with a re-manufactured Autolite/Ford/Motorcraft 4100 carburetor and a spare. The pictures are of the spare but both have the same issue as I've had the carburetor off the car twice diagnosing this issue.

Specifically what is supposed to close the primary side butterflies? There is a coiled spring around the primary shaft but on either carb the spring only provides pressure for about half the rotation. The shaft from the accelerator pump brings it closer to fully closed but is not intended to hold it there. As I found the car delivered to me, the throttle shaft was pre-tensioned to close the butterfly with the accelerator rod... however according to the 64-65 shop manual this adjustment is for accelerator pedal height, not to close the primary.

What I found is not a lack of tension from the spring but a limit to the rotation. There are built in stops on the primary shaft which limit the spring assist to 90 degrees. That said in the first set of pics the rotation is far short of closure and these shafts appear to install only one way. I seem to be missing something but not sure what it could be.

I've included pics are of the carb with butterflies closed by hand against the warm idle stop (normal position); a view with the butterflies partially open at the point the coiled spring just engages; and a view of the shop manual where it describes in the text (not shown) how to adjust pedal height. Pictures of the shaft off the carb shows the spring in its unwound position against the first stop. The other with my hand forcing the shaft to turn against the second stop

Thank you for your time and expertise!

[HeadacheGuy]

The spring in the picture you show is the accelerator pump over travel spring so the pump can spray at a controlled rate and not bind the throttle. Nothing internal closes the throttle. An external linkage spring is the only thing used to close the primaries. What is the issue you are having?

[makrie]

The engine continues to idle at high rpm unless I manually close the primary or pretension the accelerator rod in a closed direction as found prior to the carburetor rebuild. Taking the accelerator rod out of the equation the only closing force beyond the overtravel spring is provided by the diaphragm from the accelerator pump linkage. Neither close the primary side fully. The two accelerator pedal return springs provide enough pressure to pull the linkage against the bump stop behind the engine but that's all they appear to be capable of doing. The shop manual describes adjusting pedal height by turning the accelerator rod attached to the carburetor in or out. If I follow these directions I lose the pretension necessary to bring the engine to idle. I must be misinterpreting the shop manual or I'm missing a component? Any clarification will be appreciated.

[sseebart]

You should be able to get the proper pedal height with pre-tension on the carb linkage. Can you post some photos of the linkage and carb in place?

~Steve

[makrie]

Before you ask, there is an accessory lever pictured behind the accelerator connection which is not used or original to this model according to every example I can find. It spins freely on the shaft and has no bearing on this discussion.

The first photo shows the accelerator rod removed with the adjusted length adjacent to its mounting location. (see second post)

The second shows the rod installed in its most functional position but would also raise the accelerator pedal to its theoretical maximum height.

Finally shows the pedal return spring setup as found in the car when purchased. I noticed the spring closest to the firewall doesn't match the illustrations in the shop manual but does seem to perform its task.

I would like to see other examples of working setups if anyone has them to share? Thanks in advance!

[makrie]

Don't understand but this first view won't show up with message?

[sseebart]

I don't run a 4100. (I have an Edelbrock.) But I did return my car to the factory setup for the throttle and return spring. Somewhere along the way, this gets taken apart and put back together with some of the pieces missing. I have a 64, so I was missing part 9B853, shown in this diagram:



I believe for all flairs, the main throttle return spring runs vertically from the top of the linkage down to a connection on the top of the bellhousing, in your case part 7C431 I guess. Here's how mine looks:





~Steve

[makrie]

I really appreciate the pictures of an actual installation...now if I can resolve the question what should close the primarys I'll look into restoring the return spring to its original configuration. Although the spring is incorrectly mounted the accelerator connecting link is clearly against its bump stop. It and its associated linkage cannot do dual duty, apply closing pressure to carburetor and adjust pedal height. Any thoughts or additional questions are welcome!

[Popsashburn]

The spring shown in the pic is your return spring. It will return /close the primary butterflies. These are necessary on all carburetors.

[Popsashburn]

Please excuse my mess there. Just got our 64' last week. Pulled the carb today to rebuild it and clean things up under there. She's been in hiding for many years!

[HeadacheGuy]

Great pictures. Determine whether the linkage is the issue or the carb. If the linkge rod (when not attached) should spring load closing pressure beyond the hole in the carb where it attachs. If it does, the carb is the issue, If it doesn't the linkage is the issue. If it is in the carb, make sure the secondary lock out linkage is not keeping the primaries from fully closing. The pump linkage shouldn't bind you in the closed position unless something is screwed up. Check the blades of both the primary and secondaries for proper seating with the carb base off. They can be realigned if binding but it's a little tricky. Only other thing I recommend. Make sure there is a return spring directly hooked to the carb. If you depend on the rod being sprung back to hold the carb closed it is a safety issue. Rod clip breaks (mine did and the rod fell off but I had a direct spring) and the throttle goes open.

[makrie]

Originally Posted by Popsashburn

The spring shown in the pic is your return spring. It will return /close the primary butterflies. These are necessary on all carburetors.

Can you please show a picture of your attachment point on the carburetor?

I have two carbs with slightly different linkage. One appears to have an attachment point for a spring the other doesn't. Mine currently has the spring shown attached to a bracket at the rear of the carb.

[makrie]

Originally Posted by HeadacheGuy

Great pictures. Determine whether the linkage is the issue or the carb. If the linkge rod (when not attached) should spring load closing pressure beyond the hole in the carb where it attachs. If it does, the carb is the issue, If it doesn't the linkage is the issue. If it is in the carb, make sure the secondary lock out linkage is not keeping the primaries from fully closing. The pump linkage shouldn't bind you in the closed position unless something is screwed up. Check the blades of both the primary and secondaries for proper seating with the carb base off. They can be realigned if binding but it's a little tricky. Only other thing I recommend. Make sure there is a return spring directly hooked to the carb. If you depend on the rod being sprung back to hold the carb closed it is a safety issue. Rod clip breaks (mine did and the rod fell off but I had a direct spring) and the throttle goes open.

I'm not familiar with "secondary lockout", the secondaries unless under vacuum load remain closed and do not impact the primaries as configured. The primaries can be held close with any slight pressure but there isn't any source of pressure unless the accelerator link is set longer then needed to align the hole as pictured. The closing pressure is positive due to the two springs holding the accelerator linkage against its rubber stop. If I use the same linkage to lower the accelerator pedal to spec I must shorten the length by threading the rod back toward the firewall. This provides enough pull to open the primaries since there isn't a closing spring anywhere else in my existing setup.

I hope that's clearer then my original post... I would be curious to see the setup in a car that can successfully adjust pedal height without effecting idle speed.

[sseebart]

Originally Posted by makrie

If I use the same linkage to lower the accelerator pedal to spec I must shorten the length by threading the rod back toward the firewall.

Thanks, this clarifies the issue. On my car, which is close to stock, I have to lengthen that threaded rod to lower the pedal height.

~Steve

[makrie]

Originally Posted by sseebart

Thanks, this clarifies the issue. On my car, which is close to stock, I have to lengthen that threaded rod to lower the pedal height.

~Steve

Regardless of whether the rod raises or lowers the pedal what happens to your primaries if you lose positive tension on the shaft connected to the carburetor? Does your engine idle properly? Is there something else besides this rod closing the primaries on your stock setup?

Thanks in advance!