Carburetor for a '67 427/390?

[sagnoff]

Some of you may have seen my post under "burning rubber" where I was concerned about the lack of power out of my original 427/390. I have done a tune up with new spark plugs, ignition wires, coil, etc. but to minimal help. I took it to a local "hot rod" mechanic who rebuilt my friend's '67 small block vette and he thinks it's a carburator and distributor problem. My car's carb (which I thought was correct) is a Holley 600 with vacume secondaries. The mechanic drove it and said the the carb can't be original because it's to small and the secondaries should be mechanical, not vacume. Also when he moved the distributor while the car was running, it had no effect. He suggests that I put on a 750 CFM mechanical double-pumper and pull the distributor and recurve it or replace it with an MSD unit if their is one to work with a cable drive tach.

What was the original carb and what would you do if you were me?

 

[BarryK]

according to the NCRS spec guide book the '67 427/390's used a Holley model 4160 carb. Holley# R3811A and Chev.# 3906633 if the car didn't have the A.I.R option K19. With K19 it was a Holley# R3815A and chev.# 33906637.

 

[tigernut]

Post the numbers off your carb, if they don't match what Barry wrote and someone can probably let you know exactly what you have.

If your car is original, I would keep it that way if it was me.

As for increasing carb size, when we dynoed a friends 351W motor on an engine dyno, we used 2 carbs during the dyno session: a 650 with vacuum secondaries and a 750 with mechanical secondaries. The engine dyno said there was only a 15-20 hp loss when using the 650 and this engine was running 580hp and 560ft lbs of torque, so I don't think increasing the carb on your basically stock 427 will gain you that much hp.

Just my 2 cents.

Doug

 

[sagnoff]

Thanks for the feedback. If the 600 is OK, any idea why the secondaries are not opening. The carb looks to be mint or rebuilt. Maybe a problem with the vacume?

 

[tigernut]

Here is an article that may help you track down the problem with the secondaries:

http://www.chevyhiperformance.com/techarticles/67822/

Doug

 

[JohnZ]

The original 3811 was 585 CFM with vacuum secondaries, and they worked just fine; it does NOT need a bigger carb, especially one with mechanical secondaries - that's hot-rod stuff done by folks who don't understand how vacuum-secondary carbs work. You can check if the secondaries are opening by putting a dab of grease on the carb base where the secondary lever bottoms out when full open, take it out and hammer on it in first and second gear, then check and see if any of the grease transferred to the secondary lever. If they aren't opening, chances are the linkage is bound up, the secondary throttle shaft is stuck, the secondary operating diaphragm has failed, or the little circular cork gasket is dried-out or missing where the diaphragm housing attaches to the main body of the carb - that's the vacuum passage that operates the diaphragm.

The stock distributor will also work just fine, assuming the advance weights and springs are operating freely, points are OK, dwell is set properly, and the vacuum advance unit is working; there's no need for a "whizbang" hot-rod distributor.

 

[sagnoff]

Thanks. Checked my carb and it is correct with the numbers Barry posted and per the NCRS judging guide. I'll try the trick you suggestted when I get back in town and let you know.