Gasket Sealant on Carburetor Mount ?

[Tham]

Do any of those Permatex or so-called RTV
gasket sealants need to be used when mounting
a carburetor on its pad on the intake manifold ?

My usual mechanic says no, the pad is a kind
of fiber material and is not supposed to have
any sealant coated on it. He said the pad will
flex itself in place when the nuts are tightened.

However, I think my 4K's carb might have a
very small vacuum leak along its mount. The
engine idles normally when cold, but goes very
rough when it heats up. It doesn't appear to
be vapour lock.

[oldcorollas]

silicon gasket sealant (RTV etc) will absorb petrol and go all mushy.
you can use it if needed (to seal slight leak, but usually is not necessary.

there are non-silicon sealants you can use (STAG jointing compound comes to mind) which aren't affected as much be petrol...

if it idles normally when cold, but not when hot, the idle mixture might be too rich.

[oldcorollas]

and never EVER use silicon sealants to seal gaskets IN a carby. it will absorb petrol and squeeze out of the joints and do nasty things like get stick in jets of fuel passages.. all bad...

[Tham]

Thanks for the help.

One mechanic I asked also told me the same risks
with using silicon sealant in a carburetor gasket.

Apparently the carb on the 4K does not have any gasket
- there is only a black-colored fiber-type mounting plate in
between it and the intake manifold. The mechanic said
he could try fabricating a paper gasket, without any
sealant, and slide it in between the carb and the mounting
plate to try to seal any leaks.

I did write to Larry Carley, a very experienced auto
diagnostics expert at AA1car.com, and he said that my
problem sounds like my air/fuel mixture is suddenly going
lean when the engine reaches a certain temperature.
This could well be a bad intake manifold which seals
when cold but leaks when the engine gets hot.

He suggested that I use a vacuum gauge to note the
reading when the engine is started, and see if it drops
as it gets hot, which would mean a vacuum leak someplace.

I'm wondering where to take the vacuum from though.
I am using a 3K carb on my engine currently, and the
only vacuum outlet is to the distributor advance, which
has no vacuum at idle ! The stock 4K carb had another
vacuum outlet to the hot idle compensator, taken from
below the throttle plate, which would have been ideal.

[oldcorollas]

there is a paper gasket between the top and bottom half of the K series carburettor.

there should be a gasket between the base of the carby and the manifold also.
use some... 0.5?0.8?mm thick gasket paper to make this.. you MUST have one there.

on the manifold, on one of the runners, there is a little screw in plug. this is where you can get the vacuum signal..

OR, the base plate under the carby.. which has a tube that connects to the rocker cover, this can also be used as a vacuum source.

[love ke70]

what about that aviation gasket sealer stuff that doesnt dry, isnt that petrol safe?
im gonna go look in the shed, we have a gasket former thats petrol safe...

[oldcorollas]

hylomar? hmm. maybe.. makes it a bitch to get things off tho great for headgaskets tho!

[30psi 4agte]

like old corrals says the should be a gasket either side of that black fiber plate!!!!!!!!!!

all the plates i have seen are that hard there is NO WAY it will crush enough to get a good seal.

i would use permatexn on either side of each of them gaskets

[love ke70]

the one i use is loctite no.3
non hardening sealant
aviation gasket sealant
"engine assembly compound and pipe fitting cement - does not harden. resistant to petrol, oil, water, antifreeze solutions and most liquids and gases"

me thinks this would do the trick, and if i remember its what i used, i use it on most gaskets...

[Tham]

Thanks a lot, OldCorollas, 30PSI 4AGTE and Love KE70.

Wow, I don't remember seeing any gasket paper at all
on top of black fiber mounting plate when the previous
mechanic took out the old stock 4K carb - it just came off
clean - no old gasket paper stuck there, no sealant,
nothing, just a nice clean black plate at the bottom !
I don't think I saw any gasket between the plate
and the manifold as well. I wonder if it was assembled
that way. And he installed the new carb right on the plate
without any gasket in between either - just screwed on
the four nuts tight and that was it !

I'm going to get the new mechanic to put at least 0.8 mm
thick gasket paper on either side of the mounting plate
soon as I can. I'm also going to ask him to replace the
intake manifold gasket to the cylinder head.

I'll see if I can find some Loctite Aviation Gasket Sealant.
Love Ke70, is this the one you have ? Looks like
Loctite No. 30516/7. Some stores also list it as Loctite
No. 37558/9. It looks quite heavy duty indeed.

http://www.dragosupply.com/drago/ser...log/group.jsp/

http://www.hrpworld.com/index.cfm?fo...action=product

[oldcorollas]

never used it but looks like it should work... not too expensive either....

i often used red RTV on the "manifold to head" gaskets to make them easier to take off, but if you don't plan to take the manifoldoff often, this sticky aviation stuff will work

[Tham]

Apparently the previous mechanic never applied
any RTV or other type of sealant either when he
replaced my intake/exhaust manifold-to-head gasket.

Just screwed on the nuts . Not sure if he
did it in the correct sequence either.

[oldcorollas]

it is usual not to use sealant on the intake/exhaust gaskets.. i do because i remove them often... and i also have to make my own so they will fit.... i don't think it is necessary for those ones, but i would use something on the base of the carby... at LEAST paper gasket whether you use goo or not... should be ok...

[love ke70]

not that same bottle, but it looks like the same stuff
on my bottle, its only 50ml it has blue writing, white bottle, red lid. id say its the one. the part number on this one is 3J