Cant start B&S motor on old Rover mulcher

You've asked a generic question, so we can only offer generic advice.
1) How did you get it to start? That is, you didn't simply pull the cord, did you? Perhaps you sprayed starter fluid?
2) You say you cleaned the carburetor, but what does that mean? Did you take off the fuel bowl? Did you examine the needle valve? Did you clean out the jets? Did you clean out the fuel passages? Sometimes you can unclog things by shooting carburetor cleaner into the passage and watch for it to exit the other side; other times you need to poke around inside; I like to use one strand of a stranded copper electric lamp cord.
3) Is there a fuel filter? Did you check the fuel flow through the filter?
4) Is the cap on the fuel tank not letting in air (so we don't develop a vacuum in the tank)?
5) Is there a choke lever? Did you try running it with the choke on (which would probably confirm a fuel problem)?
6) Did you examine the fuel tank for garbage, sediment, or gummy fuel?
7) Is there a fine screen in the fuel tank where the fuel exits? Is it clogged?
 
The more you tell us, including what SRTsFZ6 asked for, the more focused will our advice be.
 

csigona
You've asked a generic question, so we can only offer generic advice.
1) How did you get it to start? That is, you didn't simply pull the cord, did you? Perhaps you sprayed starter fluid?

I was pressing the fuel line sort of like a primer. It will then start but stops pretty quickly.
 

csigona 2) You say you cleaned the carburetor, but what does that mean? Did you take off the fuel bowl? Did you examine the needle valve? Did you clean out the jets? Did you clean out the fuel passages? Sometimes you can unclog things by shooting carburetor cleaner into the passage and watch for it to exit the other side; other times you need to poke around inside; I like to use one strand of a stranded copper electric lamp cord.

I just removed it from the fuel tank and sprayed it with good old WD40. I blew through the tube that goes into the fuel tank and air seemed to go through. That was really it.

csigona 3) Is there a fuel filter? Did you check the fuel flow through the filter?

I don’t think it has a fuel filter. If it does I’m not sure which pet it is.

csigona 4) Is the cap on the fuel tank not letting in air (so we don't develop a vacuum in the tank)?

cap is clear.

csigona 5) Is there a choke lever? Did you try running it with the choke on (which would probably confirm a fuel problem)?

it started with the choke but then died. 

csigona 6) Did you examine the fuel tank for garbage, sediment, or gummy fuel?

it seemed clean. I did put new fuel in it as well. I doubt it has been used for years to be honest.

csigona 7) Is there a fine screen in the fuel tank where the fuel exits? Is it clogged?

not that I can see.
 Ill take the Carburettor off again and take some pictures and post them too. 
 

I agree with SRTsFZ6. It sounds like, when you said you cleaned the carburetor, you only cleaned the outside, not the jets, nor the passages. The picture you posted looks like one of those B&S units that sits on top of the fuel tank. It has no fuel filter other than a fine screen at the bottom of the intake tube. Since the fuel is not gravity fed, the carburetor has to pump the fuel up to itself. It's common for there to be a long tube leading down to the bottom of the tank and a shorter tube leading to a small well. The carburetor pumps a little squirt from the tank via the long tube and dumps it via the short tube into the little well in the body of the tank just below the gasket. The carburetor, through normal engine vacuum, then sucks fuel up from the little well through the main jet into the throat of the carburetor.
 
If I guessed right, we can identify a few things that can go wrong:
 
1. The screen at the bottom of the long tube has a lot of junk stuck on it, the result being that some fuel gets through, but not a lot. The engine would probably start, since it's pulling fuel from the little well, but quickly run out because the well is not being replenished. So check that the screen is clean. If it's dirty, also check the tank since the garbage had to have come from somewhere.
 
2. The little well is full of junk, the result being that the main jet cannot suck fuel from the well into the throat. Check that the well is clean.
 
3. The main jet is clogged. If there's junk in the little well, some of it probably got sucked up through the jet and clogged it. Flip the carburetor over and shoot some carburetor cleaner into the jet while you're looking down the throat of the carburetor. You should see cleaner shoot through the main jet passage into the throat.
 
4. The pump diaphragm is stiff or cracked. This is what SRTsFZ6 is talking about. The way that the carburetor pulls fuel from the tank up into the little well is with this ingenious little pumping mechanism. When you tear the unit down, you'll see a black gasket with a bunch of holes and a somewhat loose area (the diaphragm), about the size of a quarter, with a metal stem through it. The stem pulls and pushes the loose area, creating suction to pull fuel from the tank, and then because there are flaps functioning as one-way valves, pushes fuel into the well. With age, the diaphragm looses flexibility so it doesn't move up and down with the metal stem so well. It can also have a rip in it, in which case it will never develop suction or pressure, and so do nothing. Shine a light through it and look for holes or tears.
 
My guess for why the engine initially started is that the choke isn't only a choke (which more or less blocks the air intake) but also a primer (which shoots a little fuel into the throat), bypassing the pump diaphragm and any trouble the diaphragm might have. But after that little fuel is used up, the engine now depends upon the failing pump diaphragm, and so it runs out of fuel and stops.
 
Maybe I'm guessing wrong. Maybe I'm even envisioning a different carburetor. When you next lift the carburetor, send us a few photos of the top of the tank, and of the bottom of the carburetor, and we can be a little more sure of what we're saying.
 

The first pic, with the diaphram to the lower left, looks worn out.  
 
It should be pretty smooth...
 
https://www.ereplacementparts.com/carburetor-diaphragm-p-288247.html
 
 
,

Yes it is. One of the little flaps is worn out. Will that likely cause the issue of it not starting?

https://outdoorpowerinfo.com/repairs/

Thanks all,
Ive replaced the diaphragm and sprayed the carburettor out with a carby cleaner and now it’s running perfectly.
just need to do an oil change as it’s been sitting in storage for 5yrs+.
assuming it’s just a case of plugging some hose onto the nipple and loosening the bolt to empty out all the old oil?