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Holley carburator


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'66 327/300 hp Corvette motor with the PowerShift transmission and, I think, a 3.07 rear axle. The ignition is in good shape. It has the Holley 4160-3367 carburator which, from looking at catalogs, Corvette apparently used for a couple of years in the 66-67 era. If you've played around with this carb., you know it has several points of adjustment. I've bought a couple of the adjustment kits and am wondering if anyone has extensive experience with the setup. Specifically,

1. Which color accelerator pump cam works best?

2. Which vacuum spring? Originally, my secondary was not working at all due to the diaphragm not seating. It is now seated and the diaphragm will retract (under load) if the secondary throttle plate is disconnected, but will not retract if connected. The throttle plate does not appear to be binding at all. I'm thinking I need a weaker spring in the vacuum secondary??

3. I read that, for the 3367, take out the restrictor ball which is between the secondary diaphragm and the (carb.) body. This now allows the diaphragm to retract, as in #2 above, but I'm wondering why it was in there in the first place if it shouldn't be.

4. I've not changed the pump shot nozzle and do not know what size it is.

5. I've read that, if you run the idle jets in fully and the engine stalls, the power valve is working properly. Plus, from what I've read, this valve is apparently not as critical as some of the other adjustments.

6. I run the 93 octane gas, the highest you can get in North Carolina. Plus, it "MAY CONTAIN UP TO 10% ETHANOL." I put a bit of octane boost in the tank whenever I fill up but am not sure if it is helping. I'm thinking the gas is a fair part of the problem.

7. Which spark plug seems to work best? Platinum? Regular? Does it matter?

Many thanks for the feedback.


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You didn't say what problem/issue you are trying to resolve. Generally, the best approach is to verify that the carburetor has the factory stock parts, all clean and in good working order, set to Holley factory specs, with a fresh fuel filter. Once it's running smoothly, then go from there if you're not happy with those settings and are trying to tune for a specific condition/environment.

Can't help you directly, but here is a link to a Corvette forum search on the 3367, which should be interesting to read (includes recommendations for rebuilders if you don't feel up to that task):


Here's some hits I found on Google:




I assume your '66 would be running AC 45 spark plugs, which probably aren't easy to find these days; here is a link to some currently on eBay:


Don't settle for something that just has "45" as part of the number, except that R45 can be used if you aren't using resistor spark plug wires.

If the spark plug electrodes are clean when inspected after a run, gapped correctly, and the wires are in good shape and snug, there should be no need for fancy (expensive) spark plugs.


Edited by WayneC
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As previously mentioned, looking for a black cat in a dark room isn't productive. Define your problems. What are the running issues with the carburetor?

Personally, I've given up trying to tune carburetors without a wideband O2 sensor readout. With unleaded gas, it's no longer possible to read sparkplugs and tailpipe colors with the same degree of confidence we had in the bad old days. Get an Innovate or equivalent and all will be revealed.

jack vines

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Thanks for the feedback,guys. Basically, my problem is it just doesn't seem to idle, accelerate, run, etc., smoothly. I'm beginning to think I may be spoiled by the electronic fuel injection in everything else I own.

In the Avanti: good, even compression; ignition is good; idle vacuum, on an undamped gauge, is steady so I don't think any valves are sticking.

Essentially, I was wondering what particular setup others had found that works well -- which accelerator cam, which vacuum secondary spring, should the restrictor ball be left out in the vacuum secondary, etc.

And, is the available gas (93 octane with ethanol) a big part of the problem? Are people using octane boost and to what octane level are they trying to get the gas in the tank.

Thanks for the tips and links, guys.


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93 oct pump gas is more than adequate for your 300 hp 327. 90% of carburetor problems are ignition.

For starters check the total advance at 2500-3000rpm (with the vacuum advance unhooked and plugged), it should be 35-37°. The initial at idle means nothing to optimize the performance, factory spec advance is good safe setting for the production line.

Send Lars an email at V8FastCars@msn.com he will send you short how to tune sheet.

Check for 'Carpet Limiter', make sure when you depress the gas peddle opens the carb fully. Often it is just as simple as bending the throttle rod under the peddle to clear the carpet.

The optimum advance will give you:

1.quicker acceleration

2.more throttle response

3.engine run cooler

Then worry about the carb.


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