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Need some Help... The issue I'm having is idle hanging up around 1500.  It will lower to normal (900 rpm) if I blip throttle.  Getting tired of doing that in traffic. Middle carb is hanging , but only when engine is running. Carbs open and fully shut very smooth when engine off. Vacuum holding plates open?. Maybe it has to do with the balance tube on the cannon manifold. all carbs have been rebuilt.  I swapped carb position and problem stays in middle carb.  I heard the cannon manifold suck.  Does anyone have some helpful info for me?  TIA.

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If you pull the pedal up with your toe does that solve it?  Fast idle means air is getting from somewhere.  B;ipping the throttle just lets the blades slam shut instead of sticking on a slow close.

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Same issue on my triples with Cannon intake; was getting stuck idle no matter what I did!  After some reading, and discussion with Mike at Pierce Manifolds, I am a believer that the 3 post/rod ends are causing binding that will not be easily resolved.   Essentially, it is very difficult to get all three "holes" to line up perfectly for the rod, thus causing a bind. 

I am going to try removing the center rod post (run on 2 rod ends, not 3), increase the rod and rod ends to 3/8" and see if the linkage will be much smoother.  Otherwise, will move on to another intake manifold, if necessary.

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@Zed Head  I have a cable set up, so pulling up on pedal does nothing for me .  I'll check again for air leaks. Thank you for your time

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Hey @duffman  I tried removing the center post last year and it did not help at all.  Good luck. I just order a external spring linkage though pierce manifold (Search DCOE external spring on google) hopefully that solves it. If not I'm buying a new manifold.   I 'll let you know.  

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15 minutes ago, Rio24 said:

@Zed Head  I have a cable set up, so pulling up on pedal does nothing for me .  I'll check again for air leaks. Thank you for your time

My cable setup will still close the butterfly when I pull up on the pedal...

 

Edit: NVM, I missed the cable to bar linkage issue.

Edited by wheee!

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Rio24, I have been told that the 5/16" rod that comes with the intake is not as good as the 3/8" stainless steel rod that Pierce Manifold sells.  You may have removed the center post, but still used the smaller (thinner) rod and that doesn't work as well, am told.

 

I am also getting sticking even with the cable linkage.

Edited by duffman
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15 minutes ago, Rio24 said:

@Zed Head  I have a cable set up, so pulling up on pedal does nothing for me .  I'll check again for air leaks. Thank you for your time

That tells you that the binding is at the throttle linage on the manifold, not at the cable or the pedal.  You can extend the the thought process and push on the linkage with your finger.  Open the hood and poke around and you'll probably realize something.

Your picture shows that you have quite a bit of slack in your cable.  Seems like a good tune of the overall system might help.  Lots of adjustable bits there.

image.png

Edited by Zed Head
pole poke
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@duffman you have a good point!  Now should I try the beefer rod for 150 and hope that takes care of the issue or spend 500 on kenmeri manifold?!!  

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The total from Pierce Manifold for the 16" x 3/8" rod, 2 - 3/8" rod ends, adapters for the Cannon intake and 2 - 3/8" end links to hold the rod in place amount to about $80.  Pretty cheap alternative to a new intake (at least to start!)

Edited by duffman

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No offense intended to the guys with the problem but buying a new manifold to fix a linkage problem makes little sense.  There are three throttle blades and linkage to make them work together.  If the blades aren't sticking it's the linkage.  If a new manifold works it's because it came with new linkage.

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That is why $80 to fix the linkage is a better option to begin with, Zed Head, I agree it doesn't make sense to throw big money at it, if you don't have to!

Edited by duffman
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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

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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 by duffman
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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

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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

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

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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.

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

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@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

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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 by Zed Head

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