Holley carb issue

[shelbydoug]

One of my carbs has a leak between the inlet valve o-ring and the bowl casting bore hole.

The carb is flooding and it is not the valve seat.

I looked for a crack unsuccessfully then used a 320 grit paper roll to "clean up" the bore, even though I didn't find an issue for the o-ring to seat. It didn't help.


Here's the question, should I look for a larger o-ring, try brake fluid to expand the o-ring or replace the bowl? This time it isn't the inlet valve Drew, it's the o-ring not seating tight enough on the bowl casting.

[Drew Pojedinec]

I'm confused maybe....
the only O ring I know of on a bowl is the N&S oring.

If so, just replace that with a 008  o ring, I buy hundreds from McMaster carr....  even new needle/seats have bad o rings sometimes.
I'm happy you didn't strip out a fuel inlet again, maybe you need a bigger pipe wrench

If you mean what the o ring seats against, an 009 is stupidly loose, but it'll fit, just take great care to install slowly, and use an Oring grease.  I use Molykote 3452.

If you are crafty and have a lathe, I've had to make a stupidly thin insert to knock in there.... I made a few out of brass, pressed them in with red loctite.  But I have issues, and power tools.
I've also put a needle and seat in a lathe to cut the groove in a needle and seat for a second o ring....  cuz I get bored sometimes.

[Drew Pojedinec]

and for the record, due to your propensity in stripping out fuel inlets, I ordered some stock to thread the inside and outside on the lathe... ie making an insert to replace your broken threads.  Would need to be loctited in, and it'll be so thin it'll warp if you look at it weird.

Dunno if I'll ever get to it.... hard to say really, I don't sleep much.

[shelbydoug]

Ah. Just the soul I was hoping to hear from? So I'm not the only one who has had o-ring issues on the inlet valves? Yes the needle and seat o ring.


Confused? Hang out with me some more then apply for an SS disability account? 



I was looking around the shop for tubing on the thought of the sleeve but all I have is .049 stainless.

As near as I can tell, there is only a .002" difference for the o-ring to seat. A human hair is .004". The o-ring needs to be a perfect fit.


So the simple sane solution would be to use a larger o-ring? That makes sense but I just wanted to hit it with the 40# sledge like I do to seat the banjo bolt in the bowls? 

I don't strip out all of the threads. Out of 7 1850 carbs that I have ONLY 3 are stripped and won't tighten up.

To look at them they are not missing threads or cross threaded. I think what must happening is that there is corrosion from the ethanol and it has essentially "acid dipped" the threads. On a crazy fine thread like that, that's a killer?


Normal bolt threads will have about a .007" difference with the nut. The good ARP versions cut that to .003". It makes quite a difference and you can feel it in your fingers hand tightening the nuts.



Don't forget that the fuel transfer tube hole cuts into those treads so that in reality you are only using at most 3/16 to 1/4" of those threads. That I think is the main culprit other then this mysterious erosion on thread material.


I swear I remember Heli-coil kits from HOLLEY for them about 1972?


I've found that lubricating the threads with air tool oil works with these crazy zinc alloys the carbs are made from.
Ssssh! Don't tell anyone ok? It'll be our secret?



So are you going to call it a Shelbydoug insert? SD for short.

[Drew Pojedinec]

A lot of the fittings have a Poly type dip to help extend the chromate/plating.
It needs to be cleaned off (I use a razor blade) before install.
Zamac3 is soft enough it'll bugger up if a thread goes in weird.

Back to the n/s. There is a chamfer to aid in oring entry.
You have to make sure it is good if you make the hole larger.

[shelbydoug]

I'm using AN banjos and matching fluid bolt.

The issue is definitely on the Holley side.

I have the special 9/16-24 tap. It seems to make it worse rather then help out.

The secret is to use a bowl that still has the original Holley brass fluid bolt and banjo on it. One that has never been off since new. There the threads are as intended.

I'd guess that the three stripped out bowls I got with that fitting already removed?


I did not notice a chamfer "down in the hole". I'll look for it but looking at the o rings on the n/s after it's leaking, it looks fine with no damage.


I'm projecting that as an issue with the wall of the bowl which is what you were thinking when you sleeved them?

I'll look again for tubing. It's a strange dimension od though. Something like .319 or .320.

I have no reamers that size.

[Drew Pojedinec]

I did it because I couldn't replace the bowl.

[shelbydoug]

Do those o-rings need to be Viton or is Bunna-N ok?

The 008 is listed as a .316 od and 3/16 ID. I measure the bore at .319 to .320 stock?

The 009 is listed as .348od 11/32 ID. How does that fit?

[Drew Pojedinec]

009 is loose and requires care to not roll this why I suggest molykote.
This isn't a certain thing, more of a test and see.

Viton is fine if soft enough, avoid the really hard stuff

[shelbydoug]

I'm changing the bowl. The one I have set up on the bench, the o-ring squeaks when inserting the n/s, even with lube. So to me that indicates an interference fit. That's good.


I remeasured everything.

The bore is exactly 5/16, .312'.

The spec on the o-ring is .316", so if all is well, the o-ring will work fine.

There has to be something wrong with the bore in the bowl in question?



No one has any stock of the 008 o-rings here.

I'm not entirely shocked. By the same token, when I go into a restaurant here, if I ask for a glass of water they tell me they don't stock it and it needs to be ordered?



Now of the front carb, I have a drip coming out of the secondary throttle shaft. It must be a leak of one of the bowl gaskets and it is just running along the throttle plate and main body and just dripping there?

ALWAYS something with a Holley. When you have two on the same engine it isn't twice as much fun, it's four times the misery. They seem to feed misery off of each other more the normal Holley bs?

Of course there is always the possibility that this place is haunted. It isn't far from an ancient Indian hunting path and maybe all of my electronic gizmos have the ghost of the Indian Medicine Man pissed off?

Some things that go on here just defy logic? 

[shelbydoug]

Update. I changed out the fuel bowl and all is good. So it confirms that there is something wrong with the N/S bore in that bowl.

So that one I think needs a sleeve and I have three others that need Heli-coils on the fuel inlet threads.