T350/T250 carb flange questions

[jabcb]

The o-ring barely sticks out of the groove. That plus the typical warped flange is not a good thing.
So this morning I was wondering if:
1) has anyone put a flat washer under the o-ring? Maybe Viton or metal?
2) has anyone used a sealant on the flange surface? Maybe a Permatex that’s fuel resistant?

[markush]

Hi!

I align the flange sealing surface, leave the O-ring away and use a self-made 0.5mm paper gasket.
(Like the one between isolator and cylinder.)

[sportston]

The o-ring barely sticks out of the groove. That plus the typical warped flange is not a good thing.
So this morning I was wondering if:
1) has anyone put a flat washer under the o-ring? Maybe Viton or metal?
2) has anyone used a sealant on the flange surface? Maybe a Permatex that’s fuel resistant?

I repair the warped flange if possible and use a new rubber.
To repair the flange I use a flat diamond sharpening stone and rub the concave surface over it repeatedly, until it is level again. Then clean the flange and put in new rubber o-ring and you are good to go. I suppose for extra measure you could use some Three Bond smeared onto the new ring, but it shouldn't be necessary usually.

[markush]

I should have explained:
New O-rings should be reliably fuel-resistant.
If not, they can swell so that the thin wall of the O-ring groove will burst.
How it happened to me and can be seen here: Image 32
Since the O-ring is then not properly held anyway, I omitted it and used the said paper gasket instead.

[Vintageman]

Soak oring in atp-205 or blue devil for a bit of time. I think Oring is obsolete I never try to cross it
O RING (D:3.5,ID:31.7)

I find once the T350 carbs have been mounted onto bike and temp cycled for a while they fit better. If they have been off the bike setting in a box for a time they take a while to reform. Tighten flange nut lightly then go back after a while and recheck. I don't see any leaks