Dear Ole Mechanic;

I have two old Briggs & Stratton engines that seem to have a common problem.  The 5 HP one is on my old log splitter, and the 31/2 HP one is on my old rototiller.  The tiller is a Montgomery Ward and the splitter is a Didier; however, the equipment manufacturer is not the problem.  The problem is with the carburetors on the engines.  On both engines, the carburetor is screwed to the gas tank, and I guess the tank is the float bowl or float chamber or whatever.  I have had the carburetor and tank assemblies off of both engines and have tried to clean the carburetors.  I have not tried to remove the carburetors from the tanks by removing the screws, because I know that I will tear the gasket.  Then I will find out that the gasket is no longer available.  My problem is that both engines start OK and run as long as the choke is at partly on.  Open the choke, and both engines die.  I strongly suspect that both carburetors need a good cleaning.  Without pulling the carburetors off of the tanks, I can’t do that.Lawnmower

What am I going to get into when I pull those screws out and ruin the gasket?  Are the engines just going to be scrap?

Too Cheap to Buy New Stuff


Dear Too Cheap;

What you are going to find when you pull the screws and carburetor off of the tank, is a very tough gasket that I have found to be reusable several times.  Howeve,r it can also be the cause that makes the engines die too.  By all means, unscrew the five machine screws and separate the carburetor from the tank as gently as possible.  I say gently, because there are two plastic golf-tee looking things that stick out the bottom of the carburetor and go down into the gas tank through holes in the top of the tank.  Sometimes you need to hold your mouth just right to wiggle the plastic parts through the holes.  Don’t worry about the gasket, as it is readily available and probably in stock at any well-equipped small engine shop.  I have even seen them in auto parts stores and Tractor Supply.

When you get the carburetor and tank separated, you will see that the shorter plastic golf-tee looking thing goes into a separate shallow chamber at the top of the tank.  This little chamber is what replaces the float bowl.  There just is NO float!  The gasket that you were so worried about has a flexible diaphragm that uses pulsing engine vacuum to pump gas from the bottom of the tank up through the long plastic golf tee looking thing into the shallow chamber.  To keep the shallow chamber from getting too full and flooding the engine, there is a hole in the side of the small chamber that lets the excess gas overflow back into the tank.  To check for the most common problem, look at the gasket for cracks or splits in the diaphragm.  If you find a crack or split, then you have found your problem, as the vacuum can no longer move the diaphragm and suck gas into the small chamber.  Also, check the screens in the bottom of the plastic golf tee looking things, as they can get plugged up.  One other serious problem could be a lack of engine vacuum due to a worn out engine.  That means you will need to break down and get a new engine or a complete new machine.

As you might expect, getting the correct gasket takes the engine model and serial number.  Your older model engines have those numbers stamped into the flywheel and cylinder sheet-metal cover.  To be sure of getting the right part, I take the sheet metal cover, the carburetor, the gasket, and the tank with me to the parts house.  At least the parts person can't accuse me of giving them the wrong number.

Herr Professor Nuzanbolts