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I have a 1969 corvette 427 with the 3x2 that I’m restoring. This is my first time putting these carbs on and I noticed something funny about the linkage. They all sit fine at idle but when the throttle is hit, the first and third carburetors open initially and then close back to idle even though the throttle is pinned. I will attach some photos and it can be seen how the 1st and 3rd carburetors stay in the same position due to a sliding rail. Is this normal and they all will open up with vaccum or am I missing something? Any answers to help get this corvette on the road are greatly appreciated. This is what the linkage looks like at idle Full throttle on the middle carb with the other two still in the idle position Me pointing to the sliding rail of the first and third carbs and how it has slid up making the carbs slide to idle
they are vacuum secondaries , make sure no leaks in the diaphragms and little hoses. sometimes the lightest spring is needed to get them to work properly . The rod set up is to help close them in unison.
The outboard carbs open via vacuum only. It is not a mechanical linkage.
The linkage you mention must be adjusted correctly. They are there to ensure that the outboard carbs close when the throttle is closed (or backed off).
Make certain that you DO NOT run the carbs without the outboard closing linkage attached and adjusted properly unless you disconnect the vacuum lines from the center carb to the outboard carbs (vacuum lines are on the passenger side of the carbs). If you run them without the linkage and open the throttle with the vacuum lines attached, the outboard carbs could be in a situation where there is enough vacuum to keep them open and you can't shut the engine down - that's why the closing linkage is there.
I'm going thru my tri power now, and this thread may help. I haven't posted more to the thread because I've been out of town, but I'm back and will add some more to the post. I included how to adjust the closing linkage, a video clip from Harold Demes on how tri power's work, etc. https://www.corvetteforum.com/forums...ix-thread.html
Lars is a great resource. Rescue Rogers is very well versed on tri power and has been a big help to me.
one more question I do have is where do I hook up the vaccum for the distributor? I am running a new msd distributor I don’t see anywhere I could run it rather than the bottom of the middle carb. (See picture) Pointing to an open nipple that I believe the hose could attach to This is the distributor line
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You wont get the secondairies to open without pinning the throttle open and holding it There. Its not a good idea to free spin rev your motor like that.
As for the dizzy its best to use manifold vacuum and you have t tee off of the choke pull off. The other tee is ported vacuum and it only pulls when the carb is under load, opposite of what you want
From: At my Bar drinking and wrenching in Lafayette Colorado
As noted by the other posters above, the linkage you're fiddling with does not open the secondary carbs - it closes the secondary carbs. The secondaries are opened by the vacuum diaphragm actuators, and they are triggered by mass airflow through the center carb, which applies primary venturi vacuum to the diaphragms with the vacuum hoses connecting the diaphragms to the center carb's venturi vacuum port.
That said, it is absolutely imperative that the closing linkage be adjusted correctly. The carbs cannot be operated sfely without it. This is the factory procedure, and it is essential that it be followed precisely:
You wont get the secondairies to open without pinning the throttle open and holding it There. Its not a good idea to free spin rev your motor like that.
As for the dizzy its best to use manifold vacuum and you have t tee off of the choke pull off. The other tee is ported vacuum and it only pulls when the carb is under load, opposite of what you want
Thanks for all the help and I got it running today but not well. Still need help finding a nipple to put the distributor line to. The only two that I can find that are on that side is the one pictured above and the big one that was used for the pop up headlights. If anyone could include a picture of where theirs is hooked up that would be awesome.
I was also reviving it up and it would rev it up, stop, then catch revving up again. If anyone has any ideas about this too it would be appreciated.
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Originally Posted by Lucas Levenberg
Just above your finger is the choke pull off. IF you put a tee in that line you will get the manifold vacuum source you want. THere should be a fitting at the back of the manifold behind the last carb for the power brakes and vacuum accessories like the wiper door or headlight doors. you should replace the brass elbow with an appropriate fitting that can do all your vacuum needs
When I adjust it the way those instructions say to it races at idol.
it the throttle plates in that rear carb are open at all it won’t idol.
I am not sure they are right.
2020 Corvette of the Year Finalist (performance mods)
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I do not adjust the rear plate so that it is open. With my cam it will race and wont come down. I set the rear so that it is closed and then drop the hook into the slot for the return linkage.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
And when you set the fuel level on the floats set it low enough that you have to nudge the car to get it to slosh out. I have an Air Fuel gauge and on my set up it likes to stall when I come up to a light and put it in neutral when I hit the brakes it it is set to the perfect 14.7 AFR reading. Running it richer down near 12 it seems to be fine. I run a higher power valve so it comes in earlier when Im in 5th gear cruising on the high way or in a higher gear on rolling back roads so I dont have to down shift when it starts to go lean. If you have the center carb off check the butterfly setting and make sure that the choke isnt holding it open when you look. THe idle setting should give you a square hole so that you are in the idle circuit and not transitioning into the main circuit when you are idling. I set the idle then use the fuel mixture screws to try and get it where I want. With my cam it likes a 900 to 950 idle
1969 corvette 3x2 carburetor help.
