Gas engine float level ?

[twomany]

A couple of weeks ago, I traded in my old wood splitter for a new one. towing the old splitter over to the dealer, the crankcase filled with gas. Dumb me neglected to turn off the fuel stop.

Yesterday, I started up the lawn mower, and the engine pushed wet smoke out the exhaust for about two minutes after starting. I recall that I pushed the not running mower about 50 yards back to the garden shed after dumping the clipping bag when it was last put away. Seems that gas bypassed the float needle just like with the splitter. The Briggs engine has no shut off tap, nor a vacuum operated valve.

Any way, here is the question.

With all the vibration, jostling, bumping and banging that goes along with most any piece of float bowl served "portable power equipment", How is the fuel level in the bowl EVER maintained?

 

[Roadworthy]

As fuel is used the float sinks which allows the needle to move off its seat. This permits fuel flow into the float bowl. When the float rises it closes the needle stopping fuel flow. Sometimes fuel will bypass the needle allowing fuel to enter the crankcase through any open valve and down a cylinder wall past the piston rings. This system has worked well on many internal combustion gasoline engines for many years.

 

[Motion]

Whenever possible install a shut off valve between the tank and filter, I'm old school I prefer to run out the fuel when shutting down.

 

[lynnmor]

Your float needle is probably fouled with the crud that ethanol produces. If you let fuel to age in cans or the fuel tanks, expect problems. If tanks or cans are not kept shut, that too will be a problem, keep the lids on except while actually pouring. No, snake oil treatments will not do a thing to help.

 

[BruceP]

With all the vibration, jostling, bumping and banging that goes along with most any piece of float bowl served "portable power equipment", How is the fuel level in the bowl EVER maintained?

Have you ever been inside a carburetor for snowmobile or motorcycle? There are a number of clever 'tricks' which the carburetor engineers implement which helps answer your question.

I have seen various implementations of the following:

• Dual independent floats acting on a single needle valve
• Spring-aided needle valve
• Multiple needle valves
• Floats which 'slide' on vertical shaft instead of hinge near the float
• Rubber-tipped needle valve

Even with all of those 'tricks', I always turn off the fuel petcock and run engine dry EVERY time it is parked. I learned this whilst riding motorcycles as a youngster... just leaning on the kickstand can be enough to dislodge needle-valve and cause fuel leak.

As an interesting side-note: On snowmobiles, the bottom of each float bowl has a long (perhaps 12 inches) 1/4 inch id hose which hangs down and is plugged at the end. This serves as a large water-reservoir. You would have to get a LOT of water to fill up that hose before it gets into the bowl and affects the operation of the carb.

 

[twomany]

You know, I get frustrated.

Not a single response to the question posed.

 

[lynnmor]

You know, I get frustrated.

Not a single response to the question posed.

Here is your question: " How is the fuel level in the bowl EVER maintained? "

With the thousands of different carburetors out there, how are we to answer a question about an unknown item. It would be best if you would look up the service manual for your particular carburetor.

 

[Motion]

The level is arbitrary as long as there's sufficient fuel level to feed the high speed orifice located at the bottom of the bowl.

 

[twomany]

Here is your question: " How is the fuel level in the bowl EVER maintained? "

With the thousands of different carburetors out there, how are we to answer a question about an unknown item. It would be best if you would look up the service manual for your particular carburetor.

The important part, after the two examples


"With all the vibration, jostling, bumping and banging that goes along with most any piece of float bowl served "portable power equipment, How is the fuel level in the bowl EVER maintained?". Emphisis on EVER .

How does the needle and float work during operation, but NOT when in transport? It is certainly NOT flow rate of an open needle.

 

[BruceP]

The level is arbitrary as long as there's sufficient fuel level to feed the high speed orifice located at the bottom of the bowl.

You are mistaken. The "float level" is a VERY critical setting which dictates how the engine runs across the entire RPM range. I have been taking carbs. apart for over 50 years and have seen pretty much every type.

Not only does the high-speed jet need proper fuel-level, the pilot jet and emulsion-tube expect the level to be at correct setting. Lets not forget that the emulsion-tube needs to PREmix the fuel with air to generate 'gasoline foam' before the fuel gets into the nozzle in the venturi. The foam cannot be generated if the level is out of specification.

For most carburetors, you turn it upside down and measure using a feeler-gauge to the factory specifications. (from float to machined surface)

Assuming the jets are clean and have the factory flow-rates:

• if the level in the bowl is too low... the engine can run lean, stumble or lose power.
• If the level in the bowl is too high, the fuel will run out the overflow.

 

[Russell King]

The important part, after the two examples


"With all the vibration, jostling, bumping and banging that goes along with most any piece of float bowl served "portable power equipment, How is the fuel level in the bowl EVER maintained?". Emphisis on EVER .

How does the needle and float work during operation, but NOT when in transport? It is certainly NOT flow rate of an open needle.

You need to read post #2 that explains the system and the think about what is different between running engine and transportation.

You are assuming the valve is working when the engine was running. It could be leaking and the running engine is using the fuel at a sufficient rate to keep it out of the crankcase. Or transportation may loosen some debris that gets into the valve and then it leaks. Or some other combination or change that I can’t think of.

The root cause is gravity fed carburetor with a leaking valve. How it begins leaking does not seem to make any difference in the fact that it is leaking.

Solution is remove leak or remove the fluid source so no flow into crankcase occurs.
Removing the fluid source is the only positive solution that you can control (unless you use a valve that can start leaking!)

 

[DaveFromMi]

I've had the same problem on my motorcycle. It is a Suzuki DRZ400. I bought a gas valve and mating hoses from NAPA and installed them.
My theory is that the float bounces up and down when trailering. Since the motorcycle is not burning fuel, in my case, the cylinder filled up with gas and hydro-locked. Had to remove the spark plug and crank the gas out. Happened a couple of times before I figured it out.

 

[twomany]

Whenever possible install a shut off valve between the tank and filter, I'm old school I prefer to run out the fuel when shutting down.

That's how I shut down the Fordson!. Screw the valve down and walk away!

 

[lugbolt]

some engines are really sensitive to float levels. In particular, road vehicles (old Holleys were a good example)

Every carburetor manufacturer has a different way of controlling float bowl fuel level based on the application. Some of them were listed above. Not all carburetors have floats either. Weed eaters don't have a float bowl. They have a "float chamber" but no float inside it. Similarly, 2 stroke jet ski carburetors and snowmobiles. I hated those carbs although they were pretty simple. A lot of briggs carbs don't have floats either. I used to bore and modify them for the go-kart racers, did a lot more than just boring but you get the idea.

one thing that I kinda taught myself when i was a kid was that in tryin to figger out how a carburetor works, remember that air going into the carburetor is at roughly 14.5 psi pressure. That pressure also is what forces fuel through the jets or fuel orifices. The pressure DROP through the venturi is the key but in that area the air pressure is a little less than atmospheric--so with atmospheric being higher in the float chamber, it forces the fuel to flow from higher pressure to lower. Once you sit down and study how it works, you'll understand it.

I helped pioneer some carb modifications for turbocharging way back in the 1980's when I was a young turd. They are simple devices but the complexities in the design can through a man for many loops, and have for over a century.

 

[BruceP]

I helped pioneer some carb modifications for turbocharging way back in the 1980's when I was a young turd.

Turbocharging a CARBURATED engine can be tricky.... if the turbo is before the carb, the air-pressure into the carb can REALLY mess things up (gasoline is pushed out every orfice and even back into fuel tank) This can be avoided by enclosing the carberator inside a sealed chamber which is also at the same pressure as turbocharger outlet. The fuel in the tank must also be pressurized.

It is FARRR easier to put the turbo after the carb..... Jetting works as-expected.... however, the turbocharger has to deal with gas/air mixture passing thru it.... this poses explosion hazzards.

People who 'tune' modern electronic fuel-injected engines do not know how easy they have it. A few clicks on a keyboard can tune an engine.