Sticky idle

[Rio24]

No offense taken at all @Zed Head.  I'm sure you watched the video,  I guess I'm stuck and worried that linkage won't fix it the issue.  All linkage was disconnected and plates dont shut when engine running.  I have never seen that before!  I work on Porsche for almost 20 years and I have diagnosed sticky linkage before.  That's confusing me.  I'll definitely try upgrading linkage first.  I really appreciate you guys and you time

[jonbill]

Sounds like you just need stronger/more return springs.

[Rio24]

@duffman  can you share a link of the linkage kit you mentioned for 80?   I found this https://www.piercemanifolds.com/product_p/pm3701-l.htm

[Duffman]

Rio24, I just purchased some of those parts; the 16"-3/8" rod, 2-3/8" female rod ends, 2-3/8" end links, and 2 male adapters to secure the 3/8" rod ends to the smaller openings on the Cannon intake.   The kit has some redundant pieces that I don't need.

My issue is the 5/16" rod having binding issues with the 3 rod end set up (trouble getting the 3 rod ends to align correctly), which seems to be a common issue with the Cannon intake manifold.  Rather than upgrade to a different intake, I am going to beef up the 5/16" rod to a 3/8" rod, and reduce the 3 rod ends to just 2, thus making the linkage smoother and reduce the binding problem.

Edited August 17, 2019 by duffman

[Zed Head]

I confess, I didn't watch the videos and didn't really absorb everything you wrote.  Certain types of videos don't play well at all on my old computer and I didn't want to download it. A youtube link is better, youtube videos play well for whatever reason.  Plus the videos are too close focused they should show all three carbs at the same time, and the angled view is not pleasant.  No offense, they're just not good movies.  25% Rotten Tomatoes..

But, like jonbill said, it seems like a simple extra or stronger spring, maybe on just the sticking center carb, would do the job.  Why make it more complex?

I think that CO has pondered how the vacuum effects the backside of the blades, top versus bottom halves, if I remember right.  A sticking EFI throttle blade.  Same concept.  He might have some thoughts.  @Captain Obvious

[Rio24]

Hahaha only 25!   I've tired many different springs and placement if them. Even up to 3 spring and still doesn't absolutely fix this issue or the pedal is too tough to modulate.  Thanks for you help. The problem is beyond springs.  I ordered new linkage as someone else recommended. Hopefully that will do. I will upload thoes video on YouTube and post it here for you.  I want you to see what im talking about @Zed Head

[Rio24]

Watch both videos @Zed Head focus on middle carb actuating arm.  Watch how it sticks open and closed when shut engine down. 

[Duffman]

Rio24, after viewing your video, I don't think the issue is the rod linkage.  It looks like you might have an issue with your middle carb throttle plate sticking open, as you are not connected to anything and the sticking is occurring.  I would take the carb off and look at the back side to see if the plate sticks open on its own.  I have had to replace a throttle plate before because it was not flat and it kept sticking.  Not sure if that is your issue, but the video looks like it might be.

[Patcon]

Isn't there a spring internally in between the throats of the carb? Maybe it is weak or broken. Could be stretched

[Rio24]

@Zed Head  I rebuilt all carbs. Plates shafts bearing and seals.  They all open and close smooth as silk when engine off. Confused. Thats why I was leaner towards a new manifold

[Rio24]

@Patcon all springs were replaced with the strongest one available

[Zed Head]

So, actually two of them are sticking.  One thing that happens when the throttle blade is partially open is that any ported vacuum holes will open up.  They are typically right under the edge of the blade, Blocked when the blade is closed, pulling vacuum when the blade is open.  Usually they are meant to actuate some other valve, and not have any actual flow through them.  Just supply vacuum, no flow.  It might be that you have the ported vacuum ports open to atmosphere and the blade balance gets screwed up because of it when the blade is partially open.  

Short - check your ported vacuum ports and see if they're open when they should be sealed to a separate device.  I don't even know if those carbs have ported vacuum ports but most do, since that is how ignition vacuum advance is often controlled.  It might be labeled as "ignition vacuum advance port" on a diagram.

Edit - also, if they are connected to the distributor vacuum device the advance diaphragm might be blown, allowing a leak.

Edited August 17, 2019 by Zed Head