Dual Carb Linkage Arm Spring

[okalready]

I recently bought a 74 Ghia. It has Dellorto dual carbs. The linkage arms have springs that are too weak for the job -- engine does not return to idle, revs way too high. I can't find replacement springs. Does anyone know where I can get replacements or have another longterm fix? My shortterm fix was to hose clamp screwdrivers to the arms to increase the spring tension, but it obviously is not a real fix.

[jeffrey8164]

Those springs didn’t come with the kit.
In a perfect world no springs other than the throttle return springs on the carbs would be necessary.
In my imperfect world, I fashioned a spring onto my throttle pedal to ensure it returns as the fancy pedal assembly I got from CoolRydes does not do it on its own.
Alternatively, you can put springs from the air filter base down to the throttle shaft arms on the carb.
I got my springs from an assortment sold at Orielly.

If you zoom in you can see where I put them.
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[okalready]

That is helpful, thanks! So you just bought a random set of springs from oreilly and mixed and matched to find one that did the job? Or did you look for throttle return springs? I feel like I might be buying a lot of springs! I'm at the outer limits of my mechanical abilities here -- appreciate your input!

[rcooled]

Adding return springs like the one seen here on this carburetor to your current setup would be pretty straightforward. But note the different type of mounting arm attached to the carb's throttle plate shaft. The one in this gallery photo is designed to have both the linkage and the spring attached to it, but you may be able to work with what you've got.

[jeffrey8164]

[WrennMetallWerks]

One thing to check is the side to side movement on the long link bar and make sure it can be moved side to side by hand about a 1/8 ish. Just something to check for mobility. ☑️🤍
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[67rustavenger]

okalready,
I have several sets of Dellorto carbs. I have never needed "helper" springs on the linkage to get the engine to return to idle.
A good set of CB linkage, bases and filters are very good to get smooth linkage actuation.
Your linkage and bases appear to be from CB. That's a good thing.

A couple suggestions I can make are, relocate your coil like in some of the pics posted of others engines.
Your coil may be fowling the cross bar or rubbing against it. Causing the carbs to hang slightly open when you take your foot off the throttle pedal.

Ideally, you don't want anything routed, draped over the top of the hex cross bar. It needs to be clear of any obstructions, to operate freely.

Make sure that your throttle cable is well lubed inside the tunnel as well. The slipperier the better to help the throttle plates return to idle correctly.
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[Rome]

okal, your Dell'Ortos are the single-throat 34 FRD, often referred to as "Freds". I bought a new set back in '87 as my very first dual carb attempt. I still have them and just went into the basement to look at them. They have the same CB Performance linkage as yours. I did not see any auxiliary return springs in the storage box, but it's been so long that I don't remember if I ever had any and then moved them to the next set of dual carbs. I've had success using the spring placement like rcooled's photo, hanging the hook of the upper end over the lip on the air cleaner base.

Also many years ago I had a set of dual carbs which did not return to idle. I eventually noticed that the actuator rod for the accelerator pump was slightly bent and rubbing against the inner surfaces of its return spring. I straightened that rod so that it did not contact the inner windings of the return spring, and the slight reduction in the drag was enough to have the throttles close with whatever spring was on that setup.

It also looks like your down-rods are not symmetrical. Those are the rods going from the horizontal hex crossbar down to each carb's throttle arm. In your first photo the left rod looks tilted to the left of vertical, and the right one also. That's not good- both rods need to be set so that if either are tilted, the tilt is the same amount but mirror-image (symmetrical). Having unequal tilts causes one of the carbs to have an incrementally different throttle angle and might not be allowing the throttle plate to rest against its "closed" stop. You loose the arms where the upper joint of the down-rods are fastened, slide them along the hex bar until they are both either mirror image or pure vertical, then tighten. Use an angle finder app on your phone, or an old-fashioned angle gauge from a HW store.

Next, undo the jam nuts on the upper and lower heim joints, rotate the down rod itself (tighten or loosen the entire rod) until it shortens the overall length enough to let the throttle arms rest against the idle screw stops. Then gently tighten the jam nuts. Best to make a baseline setting on each idle screw stop so that each carb's throttle plate is at the same exact angle. Such as backing out the idle screw until you can move the throttle fully closed, then turn the screw in 1/4 turn beyond initial contact with the arm. Do this with the down-rod disconnected from the throttle arm. Then work the down-rods' length and angles per above.

Also mentioned already is to view the center arm on the hex crossbar for the throttle, that its end is lined up so that the throttle cable end is centered in the fan shroud's guide tube. If the arm, and thereby the cable is off to either side to much so that the cable rubs the inside of the guide tube, that is another friction source.

Definitely relocate the coil mounting plate down as shown on jeffrey's engine. That's the intended location and is what I did on my FRDs back then.

Here's CB Performance's diagram for dual carb linkages; it also applies to your FRDs. There is no return spring listed, but if you do need one after the above down-rod and throttle plate adjustments, get the weakest ones to bring the throttle arms back. You don't want to be pushing against heavier springs due to right foot comfort.
http://cbperformance.net/pdf/DualCarburetorLinkageInstallation.pdf

[Rome]

Also apply a few drops of 3-in-1 oil onto each of the heim joints at the upper and lower ends of the down-rods, and rotate the joints so that the oil works into the joint balls. Same with the ends of the hex crossbars. The oil reduces friction within each of those rotating parts so they don't "stick". This is part of annual maintenance...

[okalready]

Enormously helpful, thanks!!!