L-71 vacuum diaphragm question

[Kenneth K.]

[Chris H.]

Re: L-71 vacuum diaphragm question

Kenneth, I don't know about the instructions you're referring too. You mention "assembly" manual which show these cars were assembled to help workers on the assembly line. The "Chassis Service Manual" (CSM) is for mechanics to service these vehicles. That is the one you should be using. Not Holley's or anyone else's.

Many factors play into idle speed including lean/rich and ignition timing. Disconnect the linkage and then go through "the tune up" section for L-71 in the CSM.

[Chris H.]

Re: L-71 vacuum diaphragm question

Here are the steps from the CSM.

[Chris H.]

Re: L-71 vacuum diaphragm question

Another page

[Timothy B.]

Re: L-71 vacuum diaphragm question

You can start the engine and disconnect the secondary linkage and see how hard the manifold vacuum pulls the blades shut. If the carbs have been apart check to see if the blades are centered in their bores.

[Kenneth K.]

Re: L-71 vacuum diaphragm question

I disconnected the linkage and manually opened the secondaries. They close without any problems. I tried to get them to stick but never could so I think the blades are centered and there is enough manifold vacuum and spring to keep them closed.

[Kenneth K.]

Re: L-71 vacuum diaphragm question

Update - I decided to start over as suggested….

I have a copy of the 1969 CSM and tuned the engine accordingly. It runs great. Idles great. Accelerates great - seems like the secondaries kick in about 2000 rpm. I torqued the carburetors to 140 In-Lbs but could not find any torque specifications in the CSM. Does anyone have the torque specs?

The next step is the linkage adjustment. I also have a copy of the 1969 factory assembly manual specific for the corvette reprinted by Mid America. The instructions in the FAM are exactly the same as the CSM. The diagram showing the linkage is clearer in the FAM so that is what I used to setup my linkage. Please see the attached FAM diagram. Note the the diagram shows the front throttle linkage is connected first then the rear linkage. That is how I setup my linkage. However every picture I see on the internet shows the opposite. The Corvette Central web site show a clear picture of the Tripower linkage setup and the rear linkage is connected first then the front linkage. Maybe it doesn’t matter which linkage is connected first? Does anyone know if it matters which linkage is connected first?

Also my linkage has 2 teflon washers. I attached a pic that shows how I connected them on the throttle. The diagrams and pictures I have seen do not show enough detail for me to see how they are connected. Does it look like I have the teflon washers in the correct sequence?

I visited a couple Corvette web sites that sell reproduction linkage and they show the 2 teflon washers and a teflon bushing. I don’t know for sure but I think the bushing must fit on the clevis pin and ride inside the throttle bracket so there is no slack between the pin and the bracket. My clevis pin does not have the bushing and can be moved back and forth about 1/16” so that slack could be causing me problems. Can anyone shed some light on the teflon bushing?

How tight should the nut be on the clevis pin?

[Chris H.]

Re: L-71 vacuum diaphragm question

Kenneth, congrats on getting it all dialed in. Tri-Powers suffer a bad wrap sometimes, but they are really quite simple. People try to short cut the tune up process and then it runs worse, and they get frustrated. Thats why following the CSM process is so important.

Once Tri-Powers are dialed in they stay dialed in. I'll dig up a photo of my linkage.

[Chris H.]

Re: L-71 vacuum diaphragm question

Kenneth, here are my linkage photos which are slightly different than yours. I believe this is the original style setup.

carb linkage.jpegcarb linkage1.jpeg

[Kenneth K.]

[Kenneth K.]

[Chris H.]

Re: L-71 vacuum diaphragm question

Kenneth, my carb is original to the car, and I'm assuming the base plate is too. The tab seems to be some sort of guide as the closing linkage is actuated. Perhaps your base plate is from a different 2300 or maybe somebody in their wisdom decided things would work better if it was bent out of the way. It would be good of other folks with original '68-69 L-71 carbs would chime in.

[Kenneth K.]

[Danny P.]

Re: L-71 vacuum diaphragm question

Yes, if anyone else has a L-71 please post a photo of the linkage or let us know what your setup looks like.

Does your center carburetor have a bent tab or a straight tab?

What is the sequence of how the throttle rods are connected to the carburetor slot and the sequence of the teflon washers?

Is the clevis pin installed in the throttle slot followed by the first teflon washer, then the front rod, then the rear rod, the second teflon washer and the nut?

Or is the teflon washer installed on the clevis pin first and then installed on the slot in the throttle as it appears from the photo that shows Chris’s setup?

Also, does anyone know the torque spec for the carburetor to intake?

The teflon washer and rods should be free to move around you can't tighten the self locking nut too tight or replace the self locking nut, to setup carbs. I disconnect both front and rear rods, let the car run and warm up and setup the mixture and let it idle at 850 rpm. on the center carb. even go for a road test with both rods disconnected make sure it run good and idle good , then I get my front rod and adjust so it falls into secondary slot and the rear rod adjust so just half a hole short and install rod always make sure the both front and rear rods have a small play where the teflon bushing are and there no binding on the secondarys rods, I use the yellow spring on the secondarys they work best on my 67 L71 Duntov, its hard to explain with out seeing the car.17 Original and born with Tri- Power and Dated Carburators fully factory restored to spec.jpg19 All Oringinal Fuel lines.jpg

[Kenneth K.]