Leaking fuel bowl screw gaskets

[dcdoug]

I had some gas seeping past the carb bowl screw gaskets last year and would periodically add 1/4 turn on the screws and it would stop - for a while. I checked it every time I got in the car. (Carb is a 3255-1 with Lemans bowls).

So I’ve removed the carb, replaced the metering block and bowl gaskets (everything looks good and clean inside) and replaced the idle adjustment needle gaskets and the bowl screw gaskets. The previous bowl screw gaskets were white nylon gaskets, the new ones are the Holley black nylon gaskets. Carb bowl screws are torqued to 30 in/lbs. I’ve loosened and re-torqued them a couple times and checked the torque after letting it sit for a while.

I’ve filled both bowls with UV dye (PatrickT’s suggestion) to bench test it for leaking. Both front bowl screws leak (and that’s level, it’d likely be worse as my engine is canted forward). The screw and bowl mating surfaces look good. I’ve tried reversing the gasket on those screws and it still leaks (although it takes overnight to drip, so it’s just v slow seeping).

My options at this point would seem to be:

1) Torque the bolts to 35/40 and see if that fixes it (although I know the target spec is 25-30 in/lbs)
2) Change the bowl screw gaskets to the paper style
3) Change to another brand of nylon gaskets if there are any that are better
3) Try a bit of teflon tape with the nylon gaskets

Other thoughts/suggestions?

[69boss429]

I have found the original paper gaskets work best so if you have them try them.
I can't see where you could use teflon tape to help as it's not at the threads that it is leaking, is it ?
It's past the screw head, so tighten evenly on all 4 corners
You might try carefully coating the mating surface where the screw gasket is with some Rite Stuff gasket compound. Let it dry for 24 hrs before filling bowls
I have had issues like you describe in the past and these fixes worked for me

[dcdoug]

Originally Posted by 69boss429

I have found the original paper gaskets work best so if you have them try them.
I can't see where you could use teflon tape to help as it's not at the threads that it is leaking, is it ?
It's past the screw head, so tighten evenly on all 4 corners
You might try carefully coating the mating surface where the screw gasket is with some Rite Stuff gasket compound. Let it dry for 24 hrs before filling bowls
I have had issues like you describe in the past and these fixes worked for me

Right - not at the threads and didn't really see how I'd actually be able to use teflon tape either.

I was tightening in a criss-cross pattern a bit at a tie, so all bolts were being tightened evenly. Sounds like I need to order the paper gaskets and try them.

[FWB]

Doug,
honestly i've never seen them leak there.....i have the white nylon on mine, (2 x 4)
no leaks at all, maybe its the screws and not the gaskets?
do the screws fit snugly on the ID of the gaskets?

[dcdoug]

Originally Posted by FWB

Doug,
honestly i've never seen them leak there.....i have the white nylon on mine, (2 x 4)
no leaks at all, maybe its the screws and not the gaskets?
do the screws fit snugly on the ID of the gaskets?

Yes, they do. The black Holley screw gaskets were more snug than the white nylon ones were.

[FWB]

any casting flash in the counter-bore where the gasket seats?
i guess i'm reaching to substantiate the leak in my mind

[Tom Wells]

FWB,

Is there any chance the screws are a little bit too long, and bottom in a blind hole?

I've seen this with valve cover bolts...

Tom

[spdbrake]

Although I can't think of why your having this issue with the Holley seals,
Statoseals would work for your application.
All Seals Inc. - The Sealing Specialists
https://www.pegasusautoracing.com/pr...p?Product=3245
Earls Stat-O-Seal Sealing Washers | JEGS

I use them on bulkhead fittings where a normal oring just wont work.

We use them with great success in bladder type fuselage tanks.

[patrickt]

Add another five inch/lbs to your torque. If the bowl cracks around the screw hole, then it probably needed replacing anyway. The nice thing is you will know instantly if you crack it.

[dcdoug]

Originally Posted by FWB

Doug,
honestly i've never seen them leak there.....i have the white nylon on mine, (2 x 4)
no leaks at all, maybe its the screws and not the gaskets?
do the screws fit snugly on the ID of the gaskets?

Yes, they fit snugly on the screws. The black holley nylon gaskets are a tighter fit than the white ones were.

[dcdoug]

Originally Posted by FWB

any casting flash in the counter-bore where the gasket seats?
i guess i'm reaching to substantiate the leak in my mind

Nope.

[dcdoug]

Originally Posted by Tom Wells

FWB,

Is there any chance the screws are a little bit too long, and bottom in a blind hole?

I've seen this with valve cover bolts...

Tom

I've seen that with oil pan bolts. But these are the original slotted bowl screws. Don't think this is it.

[dcdoug]

Originally Posted by spdbrake

Although I can't think of why your having this issue with the Holley seals,
Statoseals would work for your application.
All Seals Inc. - The Sealing Specialists
https://www.pegasusautoracing.com/pr...p?Product=3245
Earls Stat-O-Seal Sealing Washers | JEGS

I use them on bulkhead fittings where a normal oring just wont work.

We use them with great success in bladder type fuselage tanks.

This is an interesting option if the paper gaskets don't solve it.

[dcdoug]

Originally Posted by patrickt

Add another five inch/lbs to your torque. If the bowl cracks around the screw hole, then it probably needed replacing anyway. The nice thing is you will know instantly if you crack it.

These bowls are not easily replaceable. Maybe I'll switch to the paper gaskets first before torquing them a bit tighter.

[FWB]

inspect the screws for bends in them, keeping the head from being true

[dcdoug]

Originally Posted by FWB

inspect the screws for bends in them, keeping the head from being true

I've visually inspected them, but will use a straight edge. I'll take one more look at the mating surfaces too.

[69boss429]

Originally Posted by dcdoug

I've seen that with oil pan bolts. But these are the original slotted bowl screws. Don't think this is it.

If the bolts are the original slotted ones they may actually be to short with the new gaskets as they are thicker than the originals especially the white plastic ones
I ran into that as well and found that the hex head bolts are just a bit longer allowing better bite into the threads and holding better as well
This also allowed me to retorque in place with dual fours which was difficult with slotted screws

[Shootnride]

I had one Holley that had a slightly warped metering block. This can be checked on a surface plate or with a precision straight edge and feeler gauges. A friend of mine that does a lot of work on Holleys said that this is a fairly common problem, so it may be worth checking.

Ted

[dcdoug]

Originally Posted by Shootnride

I had one Holley that had a slightly warped metering block. This can be checked on a surface plate or with a precision straight edge and feeler gauges. A friend of mine that does a lot of work on Holleys said that this is a fairly common problem, so it may be worth checking.

Ted

The benefit of the UV dye is that I can tell where the leak is coming from. Definitely the bowl screws.

[dcdoug]

Originally Posted by 69boss429

If the bolts are the original slotted ones they may actually be to short with the new gaskets as they are thicker than the originals especially the white plastic ones
I ran into that as well and found that the hex head bolts are just a bit longer allowing better bite into the threads and holding better as well
This also allowed me to retorque in place with dual fours which was difficult with slotted screws

I feel like I am getting enough bite and they are torquing properly. Black nylon Holley gaskets were def thinner than the white ones.

I think my next steps are to double check the bolts with a square to be sure they are true and the head is square to the bolt and inspect the surface on the bowl one more time. Assuming that is good, I will switch to the paper holley gaskets that arrive in a few days.

As for tightening the screws when the carb is back on the car with the Tpan in place, I am able to do it with a slot bit and a ratcheting box wrench. That's what I did last year, but I'd like to not have to screw around with it this year. (Although now that it's been an issue I'll probably check it every time I go out anyway....)