I assume that it is a twin 18. A real common issue on these are the
armatures (ignition coils) Customers a lot of the time state that the choke
helps keep them going. It isn't always a matter that they loose there spark.
Infact, the coil has a built in capacitor that times the spark and they come
out of time. Usually they start out as a hot running condition and get
worse. The partis about $50 and all B&S opposed twins use the same one.

BTW the diaphrams in the front of the carb are part of the carbs fuel pump.
(Even if the tractor has a under hood fuel tank). It is also very easy to
drop one of the 2 little springs upon disassembly.

Best of luck!

"willshak" wrote in message
...
My 18 hp B&S on my Garden Tractor won't continue to run. It is about 10
years old.
I mowed the grass a few weeks ago and it ran fine until I was almost done
with the 1 acre mow job.
It started to lose power as I was climbing a small hill in the yard, then
it died. I was able to restart it, but I had to close the choke fully in
order for it to stay running, and the it only ran for a short distance
before it shut off again.
This week, I could not get it to stay running for more than a few hundred
feet before it shuts off like it no longer got gas or the key was shut
off.

What I did:
Pulled the fuel filter off and blew through it from both ends. No
obstructions, and I could see the screen was clean inside. I blew through
the gas line that goes to the gas tank and was able to blow bubbles in the
tank.
I replaced the fuel filter with a piece of tubing, just in case it was the
filter.
I removed the gas line from the carburetor and the gas ran out freely.
I pulled the cover off the carburetor and checked the diaphragms. No
holes, tears or problems.
I ran it with the air cleaner off and the in-line fuel filter removed. No
difference.
The gas is not old and the tractor is used year round for lawn mowing and
snow blowing.

As far as I can figure, it runs out of gas or perhaps heats up to where it
seizes up. Is there an oil pump that may have gone bad?

--
Bill