Hi.

could it be too much sump oil ?

Thank you Peter. Lots of good information. I checked the engine today and I haven't been the first. It is a one cylinder OHV 18 HP vertical down shaft type. Removing the valves cover learned us that the pushers have been reversed. Alu has to be in the inlet and steel in the outlet. Wondered why.. Some tests on the head bolts gave extreme torque differences. A leaking head gasket was the main problem. Had no new one, so cleaned this one well and gave it some new life. The valves adjusted - In 0,004 out 0,005 made it run and the mowing could start. Thank you for the help from the forums.

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Answer

It is a known (by everyone in the trade but not admitted by the nice people at B & S - as far as I know) fault in that modern fuel eats through the carburetta diaphragm within 12 to 18 months. It is a 15 minute task to replce and a $5 part. They do not make a more durable diaphragm, sadly. Aparently modern fuel additives damage the rubber.

There is no diaphragm on your 18 hp Briggs. Only small lawn mowers with the fuel tank mounted to the bottom of the carburetor use a diaphragm. It is likely that the idle circuit is has some debris in it as well as the main jet. You should use Stabil gas stabilizer or Marvel Mystery Oil in all fuel used for small engines to prevent future problems. To correct the problem, go to your local automotive store such as autozone and purchase a 16 oz. can of SeaFoam. Mix 4 oz of SeaFoam to 1/2 gallon of gas...so if you feel like you have a couple gallons in the tank, pour about half the can of SeaFoam in and shake the tractor around to mix. The machine should run much better after running an hour or two. If this fails you will need to remove and disassemble the carburetor and clean throughly with carburetor cleaner, spraying trough every orifice you can find, hope this helps.
Kevin Bowley
Jim's Mowing
Expert local service for an immaculate garden
www.jimsmowing.co.uk

Alu inlet this valve only has to put up with cool air and fuel passing over it

The exhaust when open has very hot gases passing over it and has to be made strong enough to resist melting.

ps have you thought of a simple web site to advertise your rooms ?

you could then put a link at the bottom of your replies on this site.

keep well dolf

"There is no diaphragm on your 18 hp Briggs. Only small lawn mowers with the fuel tank mounted to the bottom of the carburetor use a diaphragm."

And yet, my nominal 19.5 hp Briggs & Stratton two-cylinder engine on a Craftsman 1000LT ["Lawn Tractor"] has a diaphragm . . . and uses the pressure pulses of the crankcase to actuate it. Pressure pulses, applied via the diaphragm, pump fuel through a chamber with spring-loaded one-way valves controlling flow direction.

This is fundamentally like mechanical fuel pumps once common on automotive engines, though they typically took their motion from a lever following a cam lobe (exception: VW Beetles used a tilted cam surface encircling the distributor shaft). I had that diaphragm in my hands less than 18 hours ago - checking it because my B&S is starting and dying 4 - 5 seconds later: that's why I looked at this thread! Engine started & ran fine [several hours of use] 2 weeks ago, and wasn't used in between, but does the easy-start-quick-die routine now. Give it an hour and it will do it again, but only once.

if it was a car it would be called hunting

rise in revs then falls then rises, normally caused by fuel problems carb etc

These links may provide a clue. Sorry i dont know much about this type of engine yet

http://forums2.gardenweb.com/forums/load/tractor/msg0615082010926.html

http://forums2.gardenweb.com/forums/load/tractor/msg0910373718438.html