Question on Lawn Mower with Briggs Engine

[paulegarcia_2]

Good evening,

On this engine, the carb (bowl type, no speed or mixture adjustments) is allowing gasoline to pass through and fill up the crankcase and air cleaner housing.

The lawnmower was having issues with stalling a few seconds after starting. I noted that I could keep it running by continually pressing the primer bulb; I figured it had an air leak or needed cleaning, so I decided to rebuild.

I replaced all gaskets, rubber seals, welch plugs, and needle valve & hinge pin using OEM parts. Cleaned everything with carb cleaner (aerosol). Reassembled and was still having the stalling problem (but no gas leak yet). I figured I didn't do a good enough job cleaning the carb jets and used more solvent and compressed air. Reassembled the carb again and installed.

Now the gas starts flowing. I disassembled the carb a third time and verified that none of the seals/gaskets/plugs were missing or improperly installed. Still experiencing the gas leak.

I'm pretty sure my technique isn't an issue, as I didn't have any problems after installing the new seals; only after using the compressed air did the leak begin. I can't tell where the gas is coming from, but can confirm that it isn't from the bowl itself or the nozzle extending from the bowl area into the air passage near the throttle plate.

The lawnmower was purchased in 1999 but has less than 100 hours of use. It has needed frequent carb cleanings lately. Interestingly, the engine was built one year prior to the purchase of the lawn mower (based on engine date code).

Any ideas on what's going on? Thanks.

[Andy]

Andy replies:

If you tested the float valve by lifting the float and noting that the flow cut off, then the floats are not closing the float valve. Couple of possibilities:

1) Floats are leaking or have already filled up and don't float anymore 2) Float tab needs to be bent a little more to push the float valve a little more 3) Float is binding on the side of the carb bowl for some reason. Maybe it got bent or something....

This is not an ususual problem. In my case, once, there was some crap stuck in the float valve and it couldn't shut proplerly....

A gas leak is NOT due to passageways being clogged. It IS due to faulty float valve operation, cause that's what the damn thing does......

Andy in Eureka, Texas

[m Ransley]

Its your float, it isnt closing completely alowing g s to pass. It might be dirt in the jet but reality is it isnt stopping the flow when the bowl is full. Your crankcase oil will need to be changed twice, on the second change to remove gas run it 5 minutes, the diluted oil will ruin the motor. A fuel filter would have helped.

[Jeff Wisnia]

If it's a stuck open or leaking float valve please explain how a fuel filter would have "helped". (Unless it was completely clogged ).

All I can see it doing is making it take a little bit more time for the tank to drain down to empty.

***********************************

Whilst on the question of small engine carbs, since many of my neighbors know I'm handy and enjoy helping, I get to fix a few of their mowers and snowblowers every year.

I've noticed how many carbs have evolved into ones without accessable fuel adjustments and my curious mind wants to know what the prevailing motives for this change are. I can think of a couple of reasons:

1. Some sort of emmissions control issue? (I remember near the end of the era of carbureted car engines the carbs had their idle adjust needle valves "sealed" with Welsch plugs you had to pry out to get at them.

1. Cheaper to manufacture?

Anything else?

Thanks guys,

Jeff

[Andy]

If it's a stuck open or leaking float valve please explain how a fuel filter would have "helped". (Unless it was completely clogged ).

---- Jerf

Andy writes:

I'll take this one.... The theory is that some crap may have come in with the fuel and lodged in the float valve, preventing it from closing completely ( this happened to me , once )...

A fuel filter in the line may have caught the crap before it entered the carb. This is a good bet. All the better mowers have small fuel filters in the line, and one can be bought for

2-3 dollars and added easily if they don't have one....

Remember, most gas can usually have crap in the bottom after a few years.....

Andy in Eureka, Texas

[Jeff Wisnia]

That "thwock" you just heard was me, giving myself a dope slap to the forehead.

I was focusing on a sunk float and erroneously thought Ransley was saying that a fuel filter would have somehow mollified the overflow.

Jeff

[m Ransley]

Junk from your can or whatever falls into the gas tank ends up somewhere, the jet that is supposed to seal off gas with the float can get a piece of dirt in it not alowing a complete seal. A 50cent fuel filter can save a motor from being ruined from gas diluted oil.

[m Ransley]

My neighbor used to lend out his 700$ generator till he got it back seized. Oil-gas poured out the crankcase when he went to check the oil. He thought his motor was trash since it would not turn over, when I turned it over with the spark plug removed gas shot out 15 feet. The culprit was a piece of dirt not allowing his float valve to seal off gas. Even being carefull my plastic lawnmower gas can always has junk I filter out as I fill my equipment, something I hope my new 50 cent fuel filters will catch. But why don`t all gas power tools come with filters.

[Andy]

My neighbor used to lend out his 700$ generator till he got it back seized. --- Ramsey

Andy comments: I had a similar problem with a B&S outboard boat motor (4 cycle, air cooled, single cylinder) I crank it every month and run it when it is not being used regularly, and I went to pull the starter rope and it wouldn't come.... I figured the engine had seized, or something, and was puzzled...

I pulled the plug, and found the cylinder had filled with oil. The piston could not compress it,and it felt real real real solid, like a seizure.... Well, I pulled it thru a couple times and put the plug back in, and it cranked fine...

It seems that I had left the motor in a position that allowed oil to leak around the rings over a month period. I needed to store the motor in a tilted position so that can't happen....

Just something I ran into than Ransley reminded me of, and I thought I'd mention it.... Be sure you leave your motor, or generator, in a position where this won't happen..

Andy in Eureka, Texas