OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Diaphragm being 'sucked'- leaking

Hi all,
I recently cleaned out my carbie as it was using a heap of fuel (3.5hp Briggs on a Rover cylinder model 091202 1384 E1). Replaced the diaphragm and gaskets and all seemed fine. Until i noticed fuel on the lip of the fuel tank (like it used too). Thought it may have been from the tank gasket i replaced.
Took the carbie off again and the diaphragm looks like it has been 'sucked' in between the edge and where the spring is, thus allowing fuel to virtually leak out in EXACTLY the same way the one before did
Can anyone shed any light on what this is? Note this diaghram would be 6 weeks old.
Thanks

G'day bigwal,
That's the fuel pump diaphragm, as you probably know, and I'd say your problem is that either that pump cover, or the mating surface on the carby body [less likely] has warped.

The solution is to lap the surface/s flat once more - a wetted [plain water is fine] piece of 400 or 600 grit wet & dry abrasive paper, backed by a really flat surface, is the technique to use. Move the part in a 'figure 8' pattern, until the surface is uniformly shiny.

A precision surface plate is the 'ideal flat surface', but a piece of sheet glass is very nearly as good, and a lot easier to find.

Hi Gadge,
Thank you for your thoughts. A quick trip to Bunnings in work hours picked me up a 600 grade paper, silicon spray and a glass outdoor table resulted in the attached photo. I couldn't really notice any low points, but I'm thinking a finer grade paper to smooth it out.
Makes sense with the 'gap'- i'll post back with my final OCD sanding.
Cheers mate

As Gadge noted don't forget about the mating surface on the carburetor.

Not recommended. A slightly 'rough' surface finish, such as you have, will grip the diaphragm edges a lot better than a polished finish. Which is why I specified those abrasive grades.

Now check the carby surface, as AVB has said.

You can use the cover plate as a 'flatness reference' now.
Smear the sealing surface lightly but evenly with say dark coloured grease, 'bearing blue' as used by fitters, or even lipstick, and press it against the carby surface. Then remove it, and look for 'windows' of non-contact, where the coloured paste has not been transferred to the carby sealing surface. If there are any, it isn't flat enough, and can be lapped in the same way.

Thanks Gadge- noted no more polishing. However, referring the the attached, i am assuming the pin locator is removable but I cannot for the life of me remove it to have a go at the carby surface.

When the wife asks why she smells and tastes like petrol, I'll just say 'Some guy Gadge said it was OK'

That dowel is what's known as a 'roll pin'. You have to compress it in a way that closes the slot, while pulling it outwards.
By far the best tool to use is a pair of Vise-Grip locking pliers. With those, you can compress the pin just enough, without any risk of crushing it.

As regards the lipstick, it would be best if it never returned from the shed...

Last night I tried compressing the pin with both needle and snub nose pliers, and soaked in WD-40 but to no avail. The locking pliers worked a treat, and were probably the first time those pliers were actually used in the correct way.
I'll report back when I've got myself another carby rebuild kit.
Thanks for your assistance so far Gadge & AVB.