small engine problems

[Richouse]

Ok, here is one for you mechanics...

I have a lawn mower that I'm trying to get going and the carb is dumping WAY to much fuel into the cylinder. I can take out the spark plug, blow it off with compressed air and blow the cylinder out (through the spark plug hole) and put the plug back in and it will start and run for 20-30 seconds puffing white smoke. Then it dies and won't fire back off with a pull of the rope. I then pull the spark plug out and it is dripping with fuel. What would cause it to dump so much fuel in???

Its a small engine 3.5hp or so. has a simple carb with no adjustments. Its one of those constant throttle units (vacuum adjusts the throttle so there is no manual throttle control).

I know its hard to diagnose a problem this way but I thought some of you mechanics may know something that I'm overlooking.

Thanks...

 

[bergs]

Float could be sticking wiiiiide open.

You sure there aren't any adjustments?

 

[Foxhuntr]

Maybe the float in the bowl is stuck so fuel is not shutting off. This happend to one of my mowers and it would actually shoot flames out the muffler when started.

 

[Geezer]

I'll guess it's a Tecumseh engine. They seem to have the worst carburetors.

If the fuel is old you need to drain the tank and put some fresh stuff in there.

First thing is to remove the carb from the engine and put it on a work space so parts don't get lost.

Remove the float bowl, that's the bottom of the carb. Inside there you will find a float. The float is attached by a small rod and the rod is usually free to pull out (or drop out) once the bowl is off.

The tab which mounts the float also pushes up on a shaft. That shaft is pointed at the top and serves as a valve to regulate how much fuel is in the bowl. If you allow that shaft to drop out you may find debris or something that stops it from closing completely when the bowl is full. That shaft is normally attached to the top of the tab by some sort of wire clip, so look it over carefully before you pull it out so you can put it back together.

Another possibility is that the float itself no longer floats. If it is a hollow metal or plastic float it should not have any fuel inside of it when you shake it. If it looks like styrofoam then you'll have to test it to see if it floats in a bowl of gas.

Finally, if it is a Tecumseh, there is probably a part screwed into the center of the float bowl that you can see from the bottom. Turn that screw in all the way while you count the number of turns. Then turn it all the way out and remove it. There is a spring on it to provide friction. Once it's out you can see if it is clogged with goop or debris. If so, clean it up and clean the hole it came out of. Screw it back in all the way and then back it off the number of turns you counted so it is where you found it.

Put the carb back on the engine and see what happens.

 

[Richouse]

Thanks for the fast replies...

Got the carb off. looks like its a Briggs and Stratton engine. Its a special tank that has a little place that acts as a bowl. There is a little rubber diaphragm/gasket that looks dicked up. This diaphragm apparently acts as a float. I bet if I replace that diaphragm (if I can find it) it will run like its suppose to...

The carb is bolted directly on top of the gas tank. there is no bowl

Anyone familiar with this setup????

 

[radman]

Probably a diaphragm carb, no float (ruptured diaphragm). Get a kit from a small engine dealer, use caution on disassembly, observing the diaphragm orientation. Good as new. Helpful place

 

[Ramblin Man]

I'm very familiar with that design. The carb kit is about 5 bucks from a lawnmower repair shop. The gasket has an intergal diapram in it that goes every other year at my house. I keep a spare kit in the garage just in case.

there is also a chance that the priming bulb may have a problem.

all easy fixes.