55.2-59 Carb linkage issue

[popeyestruck]

Ive been fighting with the rochestor bc trying to get it to idle . It idles way too high and wont adjust down around 1200rpm. Ive checked all the usual vacuum leaks etc . When I put the truck together I needed to make my own linkage. The linkage that goes from the bellcrank on the block to the bellcrank on the carb seems like I made it a little too long. Would this keep the throttle open too much? If I turn it down a few threads and shorten it would allow the upper bellcrank to rotate further. Does this make sense? Its acting as if I have my foot on the gas .

[1project2many]

If the linkage is holding the throttle open you might be able to feel the pressure on the linkage and on the pedal. Normally old parts will have a little play in them but if there's pressure due to the length of the rod you probably won't feel any play. At the least I think I would disconnect the throttle linkage to see if the engine idled at the correct speed before adjusting it.

Do you have a throttle return spring on the linkage? I believe he original system did use a spring. That might help close the throttle. Have you seen this post?
https://www.67-72chevytrucks.com/vbo...28&postcount=1

If I had to adjust the linkage, I might take some time to install a threaded section like a turnbuckle in order to make additional adjustments easier.

[leegreen]

Too long would hold the throttle open, that makes sense.

Most linkage like that has a Z bend in it so you can adjust the length by bending more or less.

You probably have to take it off the carb regardless, so start by disconnecting one end and see you if can get it to idle down when disconnected. Just make sure you still have a throttle return spring with the linkage off before starting.

[popeyestruck]

If you look closely at the third photo you see I threaded the end so I just need to remove the cotter pin at the top and twist the rod to shorten it. Hopefully this is the issue. Ill disconnect it first and work it by hand before I do anything. Thanks to both of you! this carb has been driving me crazy. If I push down really hard on the linkage i can get it to idle down about 100 rpms so I knew I was going in the right direction

[dsraven]

possibly a fiber carb spacer is missing or made of the incorrect thickness? that would space the carb a little further away from the manifold and doing that would mean a slightly longer rod length would be needed. just a thought. your fix works well, likely, because it is adjustable.

[popeyestruck]

I threaded to rod down making it shorter and it brought down the idle. Only problem was it kept stalling on the test drive. It will idle while parked but I need to lengthen it a bit tomorrow to find the sweet spot. Right now the rod is controlling the idle I'm getting closer at least. Before it was holding the throttle open now its holding it closed

[dsraven]

There should be an idle speed screw on there that bears down on the throttle lever to adjust the idle. Sometimes part of the auto choke mechanism, like an eccentric with steps where the end of the adjustment screw touches. When choke if fully off, or open,screw should be resting on the step that is the shortest. Throttle linkage should have a little slop in it so when body, frame or engine torques up or moves the rpm doesn't change a bunch or bend something.

[popeyestruck]

Yes There's one . I'll go over it tomorrow when I have time. Got Afib and cant exert myself for too long

[1project2many]

If you look closely at the third photo you see I threaded the end so I just need to remove the cotter pin at the top and twist the rod to shorten it.

I see it now. It looks like that would make changing throttle linkage legth easy.

It looks like there are plenty of V8 linkage kits available. It would seem like I6 linkage would be easy to find but I'm having a tough time locating any.

[popeyestruck]

Lengthen the rod about 4 turns and set the idle screw. All is well now