Weber carb linkage over-rotates and locks full throttle

dang

dang

Administrator
Site Donor
Messages
4,352
Reaction score
3,417
Location
Rocklin, CA
This subject has come up many times in the past and I've read what I could find on it, but I haven't found a specific solution. After looking at all the linkage and adjusting it different ways it seems fairly obvious that the easiest solution would be sourcing longer linkage pieces between the carb and manifold linkage. Please chime in if you feel differently.

My question is, where do I find longer linkage that will work with this style?

The video shows the motion and the two photos show the linkage attached and removed. When removed the manifold linkage sits much lower as a starting point. When it's connected it doesn't make contact with the screw stop and sits up from it's resting point. The carb linkage arm has to reach 90deg vertical to be wide open so it seems the only solution would be to lengthen the distance between the pivot points.


weber linkage full down position.jpg


weber linkage connected.jpg
 
Yikes!! I hope you discovered that when the engine was off.
Going from memory I've got another point of adjustment down below the intakes where the pedal rod connects to a pivot block with additional adjustment possible.
 
Thomas76 said:
Yikes!! I hope you discovered that when the engine was off.
Going from memory I've got another point of adjustment down below the intakes where the pedal rod connects to a pivot block with additional adjustment possible.
Click to expand...

I looked at the other linkage adjustments but realized the arm on the carb has to reach 90deg to be WOT. The arm on the manifold linkage rotates too far so if you adjust linkage down below the upper arm still has to travel the same distance to get the throttle plate to 90deg (WOT). If the link between to two arms is longer the arm on the manifold doesn't have to rotate as far to move the carb throttle plate arm to WOT.

Looks like it would probably work if the arm on the carb were shorter also. I haven't drawn it up.
 
Last edited:
My car does this, but I have no reason to address yet. In addition to your linkage updates, make sure that you have the spring on your engine mount linkage pivot.

Check out the site below. If you order anything let me know. I need a Weber TPS sensor for my triples.

 
This happened to me on the interstate back in the day the first time I took my newly swapped Zeniths for Webers for it's test drive. That's why I always warn people about this conversion. Anywho, you might try Pierce Manifolds (a little closer to home) for some longer adjstable linkage:

Weber carburetor Authentic Weber Carbs, Manifolds, Conversion Kits!

www.piercemanifolds.com www.piercemanifolds.com

Also, that stop screw you show is not the throttle stop screw, it is used only for getting the engine up to the rpm to check timing (1700 rpm?), it is not used for setting idle. That is done on each individual carb throttle stop/screw. These along with idle mixture are what you'd use for balancing/idle adjustment.
 
Stevehose said:
Also, that stop screw you show is not the throttle stop screw, it is used only for getting the engine up to the rpm to check timing (1700 rpm?), it is not used for setting idle. That is done on each individual carb throttle stop/screw. These along with idle mixture are what you'd use for balancing/idle adjustment.
Click to expand...

Understood. I didn't mean to imply that it was an idle adjustment but it will help the over-rotate problem by starting lower in the rotation. With the adjustment screw all the way in there's still about a 1/4" gap, so it should help quite a bit.

Thanks for the suggestion.
 
Is it possible to address this using the stop at the bell crank? My car had been converted to dual downdraft Webers before I bought it, and did not have the stop on the bell crank. (I added it to reduce stress on the spindles with my particular linkage setup on the triple Webers).

You might check whether the stop could limit the downward travel of the lower end of the lower lever, which would in turn prevent the over-rotation of the upper end of the lever.
 
Is the problem simply the clocking of the arm mounted to carb? Mine looks different.

IMG_20210301_175015385.jpg
 
Spare carbs in basement same thing. This pic is wide open throttle, look at the difference of where the zinc arm is in relation to yours. Not saying it fixes everything but could be incorrect arm?

IMG_20210301_180358101.jpg
 
Thomas76 said:
Spare carbs in basement same thing. This pic is wide open throttle, look at the difference of where the zinc arm is in relation to yours. Not saying it fixes everything but could be incorrect arm?

View attachment 112688
Click to expand...

Yes, this is something I considered but couldn't find enough photos showing it. Not sure what my arms are from, they came with the carbs. I would prefer to pull up on the carb arms then to push them up.
 
dang said:
Yes, this is something I considered but couldn't find enough photos showing it. Not sure what my arms are from, they came with the carbs. I would prefer to pull up on the carb arms then to push them up.
Click to expand...
Sorry I don't have a paper trail of where my arms came from, they do pull up on carb. I just looked on Pegasus and Pierce but didn't see anything that looked right.
Let me know if you need better pics of these arms.
 
Hey Dan, I know we take these linkages for granted, then when something goes wrong, it is difficult to get some photos to help see what may be amiss. Here is a photo of my 32/36 linkage. Sorry it may be a bit dark, but perhaps there is something you notice here?
5ED1E2C8-23D0-4769-9C6B-AB04711DE428.jpeg
 
The arm shown in Thomas76 post #9 looks like the ideal solution. But where do you find an arm like that? One alternative might be one of these universal arms that Pierce sells as product codes: 99005.316 and kc247 :

99005.316-2T.jpg
KC247-2T.jpg


I've never tried these parts myself, though I'm tempted to try one, so my rods are pulling rather than pushing.

I'll take a photo of my current solution and post it tomorrow, though I'll concede that it's a bit crude (see post #19 below). From memory, thicker thermal isolators between the manifold and carbs will lessen - but not solve - the over-centering problem.
 
Last edited:
I discovered this issue when I was rebuilding my Webers. At the risk of under-thinking the problem, I welded this little piece of steel onto that first lever (this photo is taken from the front side of the front carburetor). It is precisely positioned to mash into that screw when the secondaries are most of the way open. And now that screw has a purpose again; turning it adjusts the stop position.

IMG_5673.jpg

For what it's worth I'm still not brave enough to put more than the normal amount of pressure on the pedal at full throttle.
 
Blinkling said:
I discovered this issue when I was rebuilding my Webers. At the risk of under-thinking the problem, I welded this little piece of steel onto that first lever (this photo is taken from the front side of the front carburetor). It is precisely positioned to mash into that screw when the secondaries are most of the way open. And now that screw has a purpose again; turning it adjusts the stop position.

For what it's worth I'm still not brave enough to put more than the normal amount of pressure on the pedal at full throttle.
Click to expand...

Clever solution. I considered putting a bracket/stop mounted off of the motor mount since there's a few bolts in the right spot but in the end I wanted to know that the linkage couldn't physically over rotate and lock, just in case for some reason the stop didn't work. My test plate link proves that it's a simple fix, in my case it's a 50mm ball/socket rod to do the trick.
 
OK, here's a couple of photos of my crude solution. Like Blinkling's fix, it involves creating a stop so the linkage can't go far enough to get into the over-center condition. Instead of welding on a piece of metal, I added a screw + stack of nuts that contacts the linkage base plate. Here are photos of the linkage at rest and at (almost) wide-open throttle.

Throttle linkage (2).JPG
Throttle linkage (3).JPG


I apologize for how grubby/corroded everything looks! My coupe has basically been on the road since it was sold in 1970. Re-painted, re-upholstered, maintained but certainly never fully restored.
 
Back to the question of re-jiggering the linkage so that the short rods pull the carb lever upward rather than push it upward. Thomas 76 and bluecoupe30! show this sort of set-up in posts #9 and 15 respectively. But there are two things different about their linkages:

- The arms on their carbs are oriented more downward than the arms that came with the Webers as part of the JAM kits. But you can't position them too far downward, or they will interfere with the manifold runner.

- The arms on the rod that pivots on the manifold are oriented more upward. I can see how this was done on bluecoupe30! set-up; his linkage is clearly aftermarket. But how was it done on Thomas76's? Were the arms somehow cut off and re-positioned on the rod? Or can you achieve this just by shortening the long rod that comes off the bellcrank on the side of the block? Here's a cropped version of Thomas76 picture. Notice how the arm that pulls the short rod upward sits higher than stock:

Throttle_linkage_4_cropped.jpg
 
Last edited:
You must log in or register to reply here.
Back
Top