Briggs engine running rich

[Mr Mower Man]

I have a Troybilt tiller in the shop with a 5HP Briggs (135202-1015-E1, Date code 001003YA). It's kinda hard to start because it floods very easily. And when it does run, it sounds pretty rich. After it runs about 3 or 4 minutes, it starts to sound better, but it still runs ever so slightly on the rich side. This is one of those engines with the carburetor diaphragm right next to the muffler, and the diaphragm was easy enough to access, so I put a new one on it to see if that would fix the problem before I went to the trouble of removing the carburetor. The new diaphragm didn't change anything. As I looked closely, I noticed that the diaphragm plate looked like it was bowed out away from the carburetor body in between the screws that hold it on. I could see the diaphragm between the plate and the carburetor body, and it looked kinda wavy like I think it wouldn't be if it were securely held between two hard surfaces. So I'm guessing the diaphragm plate, being next to the muffler, has been warped. Would this cause a rich running condition? I don't have a bunch of experience with this older style of carburetor.

[KE4AVB]

So I'm guessing the diaphragm plate, being next to the muffler, has been warped. Would this cause a rich running condition? I don't have a bunch of experience with this older style of carburetor.

That diaphragm is primary the fuel pump but engine vacuum could pull surplus fuel pass if leaky especially if the cover plate is warped.

[Mr Mower Man]

I called Briggs tech support, and the guy told me that these engines will tend to run rich if compression was weak. I checked the compression, and it was awful. In fact, when I pulled the head, I could place my thumb on top of the intake valve and rotate it at TDC. I'm going to finish the valve job and then see how it runs before I do anything else with the carburetor.

[Merkava_4]

As I looked closely, I noticed that the diaphragm plate looked like it was bowed out away from the carburetor body in between the screws that hold it on. I could see the diaphragm between the plate and the carburetor body, and it looked kinda wavy like I think it wouldn't be if it were securely held between two hard surfaces.

Did you line the diaphragm up with the cover plate before putting the first screw in ? I take a small center
punch and shish kabab the cover plate, diaphragm, and screw holes - before putting the first screw in.
I've had those diaphragms wrinkle up just like you described and it was because I didn't have all the holes
lined up square. On that Horizontal Pulsa-Jet diaphragm cover, we're only talking about 4 screws.

Does that carb have the pilot jet, or the adjustable mixture needle ? The parts drawing shows both.