I have a 69 427/400 that has never really run quite right and I think I've narrowed it down to the carb(s). When I first got the car it would pop at idle out one side and did not accelerate like I expected. I thought it might be a bad cam so I took it to a rebuild shop and they said the oil pressure and compression were fine and they adjusted the center carb because they said it was "dumping way too much fuel in" at idle. It ran better but still never felt dialed in.

This is what I have done to it so far:

1. Replaced the timing chain.
2. Replaced the spark plugs, wires and coil.
3. Rebuilt the distributor.
4. Replace the points with electronic, in the distributor, system.
5. Reset the timing.
6. Replaced all three carbs with brand new stock holleys.
7. Replaced the vacuum lines.
8. Checked the vacuum advance.
9. Replaced the fuel pump.

Here's where I'm at:
The car idles quite roughly with black exhaust. Accelerates well off the line but starts to "miss" and not accelerate well at about (the tach cable is broke) 3000rpm on up. At highway speeds it accelerates poorly (misses) when I punch it.

Another notes:
The secondaries are kicking in (I can hear them and it sounds awesome). I don't remember exactly how I setup the center carb and I don't have any instructions around.

Does anyone have carb setup instructions or other ideas or can someone recommend a great tuner in the Detroit area. I'm dying to have this thing sing!

 

What did you do with the OEM carbs? Did you replace like carbs for like carbs or use some without vacuum to open the end carbs? The OEM units do not have pumps or adjusting screws in the two outboard carbs.

 

IF its popping out of one side of the exhaust at idle, one of the idle air bleeds are not set right. Normally thats a lean condition. Tri-powers I have heard are a biotch to tune right. Your problems sound like they are DEFINETLY in the carbs.

 

When I bought the car 20 years ago it had a 390hp manifold and 4bbl even though the block stampings near the water pump and console stickers said it was a 400hp/tri-power car. I put the correct manifold and three brand new holley carbs on about 12 years ago. The outboard carbs have large vacuum diaphrams and they do not have pumps or adjustments. They seems to be opening and working fine.

Right now I think I have fouled plugs. It is barley idling after the first drive a couple days ago. It's really chugging and very black/gas smelling exhaust. My next step is to put new plugs in, again.

I don't think I have ever had the center carb right. If the plugs get it running decent again I want to work on the center carb. Does anyone have step-by-step setup instructions for tri-power carbs? I would also be happy at this point to turn it over to a professional if anyone knows of a good carb/tri-power shop in Detroit area.

 

Don't miss this. Even if your car is not tuned you will learn a lot. The LT-1 on the list should have a Holley carb. Maybe no tripowers in the mix, but still well worth attending.

http://forums.corvetteforum.com/show....php?t=1369238

 

Just did a google search and you might be interested in the $5 e-book

http://carburetor-manual.com/chevrol...961-p-299.html

Just noticed that is for the orig Rochester version but still might be usefull

 

New plugs did not help. Old ones were coated black and wet. It's idling like a Harley, glug glug, glug glug with black tail smoke. Barley staying running at idle. I took it for a short drive after the new plugs and it is accelerating better when I punch it but not really drivable at low speeds and stop signs. Two days ago it was idling smooth as silk until the last corner on way home when it stalled and started idling very badly.