CB Crossbar

[croSSeduP]

I searched the forums, didn't find what I was looking for really. I've set up this linkage a handful of times in the past, but this time I've run into a problem that has me scratching my head. I have it set so that both carb arms leave the idle stop at the same time, but the 1/2 side reaches WOT at least 3mm before the 3/4 side. I've monkeyed with it in various ways and haven't been able to solve this.

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[Brian_e]

Hard to tell from here, but it looks like you have a spacer under the upright linkage arm only on the drivers side?

The linkage arms need to be at the exact same angle looking from the back, AND looking from the side. They will swing in different arcs if the angles aren't the same.

The length hole center to hole center, on the small arms attached to the carbs also need to be the EXACT same length.

Brian
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[Ohio Tom]

Loosen the set screw on the 1/2 side arm. Slide it towards the center about 1/4".
Tighten setscrew and re-adjust pushrod.
See if that helps, or hurts.
Tweak accordingly.

[jpaull]

Do yourself a big favor and get rid of those flimsy throttle levers and get some of these CB true position levers for $35. Money well spent. Not only are they more strong, but they are also likely something that fixes your issue.

https://www.cbperformance.com/product-p/6460.htm

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[Alstrup]

Also, I have found that the 3-4 side throttle arm has a tendency to flex due to the extension. I have solved it by having 2 throttle arms on the 3-4 so it becomes stiffer.
- Ohh, Jeff beat me to it. Those are nice. Never tried those, but they will be on my next shopping list fershure.
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[k-weaver]

I've had this happen on a set of IDFs. The issue for me was the throttle lever. It was loose because it was old and just worn. So the arm/lever would move independent of the actual shaft. Not much, but enough to present the problem you are describing.

Your carbs look relatively new/rebuilt so I doubt that is the issue but figured i'd throw it out there just in case.

[croSSeduP]

Here’s a closer pic of the 3/4 side. The spacer is needed with non-offset IDA manifolds. Also, I wouldn’t call the throttle levers cheap. They are stout. I got them from JayCee. Still working on it. Will post pics of what I did if I fix it.

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[croSSeduP]

[Brian_e]

The linkage lengths have nothing to do with it. It is all arc swing geometry. You have some linkage angles that are not correct, or your full throttle stops are not the same and making it look off.

Look at the vertical linkages from the side. Make 100% sure they are the same front to back angle. I have never seen one of those spacers the correct length out of the box.

The angle finder in an iPhone works well for this kind of thing. Also check the side to side angle with the angle finder. Tiny angle differences make a big difference.

Brian
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[74 Thing]

What do the butterflies look like when you hit the full throttle stop? Are they both the same or one a bit behind just like the linkage?

I'd loosen and remove the throttle arms on the carbs and compare one to another-is one longer or is the installation hole ovaled out allowing different starting angles?

I had one that had a stress crack that I could not see that caused the problem.

[vwracerdave]

Another suggestion is to throw the cross bar linkage away and get the CSP Bellcrank linkage,
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[Dale M.]

[mcdragracer]

Providing that your geometry with the angle of your rods are the same on both sides, one thing to look into which I have seen a few times is the clocking on the outer arms, I have found some that were casted off and that were clocked in a different position than the opposite side allowing one to open sooner than the other one by a few degrees, allowing 1 carburetor to open Full Throttle sooner than the other side .
There would be an easy way to check this, remove the hex bar and loosen the arms and slide them together and look down the middle to see if they are both in line or if one is clocked off from the other.

[YDBD]

Did you check the flat arms that mount to the shaft? Are they exactly the same? Do they fit tightly on the shaft with out the nut being tightened or is there play? Those are just stamped metal and may be off just enough for a 3mm error at 3cm out from the center pivot point. I don't think I've ever had one that did not wiggle.
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[croSSeduP]

I don't know how to multi-quote on this site so I'll answer questions the old-fashioned way and give an update -
Nothing wrong with the throttle arms.
I checked the outer arms/flat arms. Nothing wrong with them. They are mirror images of one another, and they fit tight because I added a set screw so that they can't wiggle.
BUT, here is one thing I've found,,,The down rod on the 1/2 side angles in a hair more than the one on the 3/4 side. I can add spacer washers between the heim joint and where it bolts to the throttle shaft to flatten out that angle to more match the 3/4 side and see what happens.
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[Brian_e]

[74 Thing]

Maybe using a protractor or angle finder to make sure the down rods are vertical when viewed from behind and then at the same angle when viewed from the side.

When I had neither I would cut a piece of cardboard and use as a template so one side matched the other.

[croSSeduP]

Here's what I did to solve this issue. It seems a bit extreme, but given all the other possibilities, and trying all the things suggested by all of you marvy people, here's what I did. On the side that wasn't reaching WOT I slotted the hole the other way. I put a split washer between the nut and the arm to lessen the possibility that a slippage could occur. It solved the problem. But, I've found a new one that I'll post in a new thread.

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[Dale M.]

[Brian_e]

Agreed That much return spring is hiding another issue. Take the throttle cable loose and see if it returns nice an easy with only one spring. Lots of guys have a tendency to pull to hard on the throttle cable while hooking it up. Then it always wants to pull a little bit. A little slack in the cable isn't a bad thing.

A good, stable idle that returns to the exact same spot is 10x more important than getting that last 1/16" of throttle travel.

Brian
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