Holley tri-power nut size

[John C.]

The recent thread on the availability of a special carb wrench to hold the carb nut on a Holley tri-power while tightening the fuel line fare nut brought up a question for me. What is the correct size nut?

I have 12 Holley tri-power carbs. They are a mixture of originals and service replacement. All have been rebuilt at some point in there life. Nine of them have a 1 inch nut and three have a 13/16 inch nut. The nuts are also machined differently as shown in the pictures. Anyone know which nut/size is correct?

John

[Michael C.]

Re: Holley tri-power nut size

The first photo looks to be original size and configuration.

[Joe L.]

Re: Holley tri-power nut size

The first photo looks to be original size and configuration.

John and Michael-----


I agree. The first photo depicts the fitting that I believe was originally used. The fitting in the second photo I believe is a much later replacement, probably designed to avoid the wrenching problems of the original style.

[Wayne M.]

Re: Holley tri-power nut size

These are on an original tripower setup I have; late-ish '69 production dates. 13/16 hex with a thin steel gasket.

2 x 3659 9_5_1
center 4055 9_8_1

[Joe L.]

Re: Holley tri-power nut size

These are on an original tripower setup I have; late-ish '69 production dates. 13/16 hex with a thin steel gasket.

2 x 3659 9_5_1
center 4055 9_8_1

Wayne-----

Well, I decided to look further into this. I always though that the fittings on the Holley fuel bowls were the same for all dual inlet carbs.It turns out that there were at least 3 of these fittings used as follows:

GM #3889776-----65 L-78, 66 L-72, 68-69 L-88, 70-72 LT-1

GM #3890124-----67-68 L-68, L-71

GM #3960299-----69 L-68, L-71, 71 LS-6

I don't have any known originals of these part numbers so I can't say, for sure, what the configuration of any of them is. However, presumably, the 1969 carbs you show are the 3960299. The "fly-in-the-ointment" there, though, is that I have a Holley re-issue of the 1971 LS-6 carb. That carb is also supposed to use the 3960299 but the one I have has the 1" across-the-flats fitting. Of course, it may be that this feature on the carb is not correct but the rest of the carb is very correct.

By the way, I've always used a standard 1" open-end wrench on these fittings without any real problem. It does not fit perfectly but it serves the purpose OK.