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'67 427 435 tripower idle problem

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Old 02-16-2017, 05:33 PM   #1
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Default '67 427 435 tripower idle problem

Hi, guys,

I'm new to the thread. I just finished a one year partial resto on a '67 427 435 roadster that I bought from the original owner. His name is on the protecto plate, car has the build sheet etc.

This original owner took the tripower off in '69 because he couldn't get it to run right. But all of the carbs, manifold, air cleaner, etc. came with the car. As did the California-only for '67 smog equipment.

So we built the engine back totally stock, stock bore, cam, heads, etc, had the transistorized distributor redone with a new upgraded electronic board, and dynoed the engine. On the 6th pull, it made 453 BHP and 460 lbs-ft of torque.

So here's the deal: on the dyno, the engine would idle down to 800-900 rpm, no problem. Now that it's on the car, it won't idle lower than 1700 rpm. All that we added to the engine after the dyno is the smog equipment.

So I googled tripower problems, and some answers led me to really great info on this site, such as connecting to manifold vacuum instead of ported vacuum. When I start the engine, I can flip a#2 pencil upside down and use the eraser end to press on the front carb butterflies and no change in rpm. When I do the same thing to the rear carb, the idle immediately starts coming down to normal-depending on the idle adjustment screw on the center carb.

So obviously, something is messed up with the linkage/vacuum pots, etc. These carbs were rebuilt by Holley. The car drives really great and is super responsive.

The rear carb butterflies seem to me to be cracked open. How do I adjust and/or fix?

Much thanks,

Jack in Memphis, TN
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Old 02-16-2017, 05:41 PM   #2
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The throttle linkage between the center carb and the front/rear carbs should have a rod of some sort between the center carb throttle lever and a lever on each of the front and rear carbs. The rod closes the outer carb throttles when the center carb throttle lever is fully forward (throttle closed). Sounds like the rod to the rear throttle lever is too short and doesn't force the rear carb throttle closed. The adjustment is made by unthreading the rod end from an internally threaded tube connected to the center carb throttle lever.

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Old 02-16-2017, 05:50 PM   #3
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disconnect all linkage to the end carbs and use a spring to hold the throttles closed. if idle good adjust linkage rod to fit.
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Old 02-16-2017, 06:04 PM   #4
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also make sure your choke is not sticking
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Old 02-16-2017, 10:01 PM   #5
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Thanks to all. The rod between the center and rear carb was not quite 1/16"
short. We adjusted by threading out and the idle came down. It tries to die sometimes, so tomorrow I'll check the fuel bowl gas level and use a vacuum gage to adjust the mixture on the center carb.

Jack
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Old 02-16-2017, 10:19 PM   #6
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Default 3 x 2 linkage adjustmant procedure

Here's the tri-power secondary linkage adjustment procedure from the 1969 service manual. 67 & 68 are exactly the same.


RON




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