L-71 vacuum diaphragm question

[Danny P.]

Re: L-71 vacuum diaphragm question

Danny -

That’s a beautiful tripower. Thanks for posting the photos.

It’s hard to see in the photo but it looks like the tab on your center carburetor is bent down so when you let off the throttle the tab pushes down on the front linkage rod. This would keep the linkage from riding too high in the slot when it is at idle. My center carburetor is dated 821 but have no idea why the tab is not bent down. That may contribute to the occasional 100 - 200 rpm high idle I experience when my rear carburetor throttle plates don’t close completely.

The other reason the rear throttle plate may not close all the time could be the sequence of how I assemble the linkage. I can’t see from your photos if there are 2 teflon washers. Can you tell me the sequence of how the rods and washers are assembled or post a close up of the linkage that shows the clevis pin, washers and tab?

ken, my tab is down because it control the swing of the center linkage close properly i see yours is up maybe when throttle coming down center linkage its jamming up and making the secondary stick, next time it sticking at 200rpm higher at idle check at the center linkage if you wiggle the linkage and it drops rpm that where your problem is , both rods should swing nice and smooth up and down without binding in the channel and make sure the teflon bushing are not too tight, when i did my PV test I had to let it go at 5800 rpm and then had to Idle at 800rpm .19_InPixio.jpg

[Danny P.]

Re: L-71 vacuum diaphragm question

Danny -

That’s a beautiful tripower. Thanks for posting the photos.

It’s hard to see in the photo but it looks like the tab on your center carburetor is bent down so when you let off the throttle the tab pushes down on the front linkage rod. This would keep the linkage from riding too high in the slot when it is at idle. My center carburetor is dated 821 but have no idea why the tab is not bent down. That may contribute to the occasional 100 - 200 rpm high idle I experience when my rear carburetor throttle plates don’t close completely.

The other reason the rear throttle plate may not close all the time could be the sequence of how I assemble the linkage. I can’t see from your photos if there are 2 teflon washers. Can you tell me the sequence of how the rods and washers are assembled or post a close up of the linkage that shows the clevis pin, washers and tab?

Hi Ken, this is a closer shot of my linkage with the Teflon bushing , I think you have your bushing set up wrong according to your photo, bolt goes through the throttle linkage with 1 bushing then rear rod then bushing then front rod then self locking nut and a little tab of white lub on teflon bushing , look at the photo my linkage that I sent you.DannyL71.jpgDannyL71.jpg

[Kenneth K.]

[Danny P.]

Re: L-71 vacuum diaphragm question

yes just a small tab of lub in between the both teflon bushing where it ride up and down the channel not much , try the way i have it set up and see if it works let me know .

[Kenneth K.]

[Danny P.]

Re: L-71 vacuum diaphragm question

great to hear Ken , it doesnt matter which rod goes first as long as set up right and working good that all it matters , my set up is a 67 Tri-power L71 it works great for me .

[Chris H.]

Re: L-71 vacuum diaphragm question

Ken I found a couple more photos from my library that I found on the TDB at some point in the past. File name(s) is 'L68_late_69"

[Chris H.]

Re: L-71 vacuum diaphragm question

69L68linkage-1.JPGL68_late69.jpg

[Kenneth K.]

[Thomas S.]

Re: L-71 vacuum diaphragm question

Some very helpful info in this thread. There are no similar details in the 1967 GM service manual for this. Would it be safe to assume that the tri-power linkage adjustment detail and other linkage mechanical comments are correct for a 67 L68?