pressure testing a carb

[forest tink]

just a wee query,have a carb off a 346,pumped it up to about 7 psi,it sits there for a second or 2 then drops away down,tried it submerged in petrol and theres no apparent leaks,is it normal to drop pressure or should it be holding the pressure?

[Dan Forsh]

As far as I'm aware, it shouldn't drop. Either the inlet needle is worn or diaphragms and gaskets need checking. Or what you are pressurising it with is leaking maybe?

[forest tink]

everything seems airtight,put new carb kit/needle valve in and made little difference,no leaks but pressure drops

[spudulike]

They tend to either Pop on the big carbs or leak down slowly on the smaller carbs. If you submerge the carb, it should be blatantly obvious where the air is going to as the air must be going somewhere!

 

Carbs tend to leak a little but much less so if there is fluid in them.

[adw]

Are you sure your pressure tester is not leaking, with fuel in the carb you should see no leak with slightly less pressure than you are putting in there.

[forest tink]

how much pressure would you use ?

[adw]

3 or 4psi is more than enough, many manuals talked about pop off pressure ( pumping up until the needle lifted off its seat ) but this stopped as it could damage the pump diaphram.