Microlighters

Hi All,

Yes me again, come to ask more questions...about carbs...Wow

I have recently serviced my carbs, took them apart and replaced the Jet needle and needle jet, the float needle valve and the air filters. The problem I am having..she's one...

I make sure the fuel in the float bowls are at the correct level, start the engine and the 503 purrs like a kitten, the acceleration pickup is also smooth and constant, but when I leave it to idle, the idle drops to about 1500RPM,

I then switch off, check the bowls and there you have it, flooded, over full, fuel to the brim...

What could cause that? Any help will be greatly appreciated.

Fly Safe

Gary

If this is not set properly, the float needle will not press hard enough against the float needle seat and the fuel will fill the float bowls and overflow through the vent tubes. Alternatively the fuel level will be too low in the bowls leading to fuel starvation

Adjust by bending the part that activates the float needle valve. If you bend this little plate up (when the carb is upright) the float needle will meet the seat sooner and the fuel level will be lower in the float bowl. If you bend this down the fuel level will be higher

Hi Greg,

Once again I say thank you, I will give it a try. I will also replace the floats as I am sure the current floast are taking strain. I will let you know the outcome.

Fly safe

Gary

Hi Morph,

Just a quick question, with the float bowls flooding like that, will it cause the engine to idle so low?

Also check if both floats are actually floating with fuel in the bowl. I had floats become "sinkers" before.
One active float in the bowl alone cannot close the needle & seat valve properly.
It can also be a case of the floats sticking on the centre pins, which may be solved by cleaning it properly.

Alpha wrote:Hi Morph,

Just a quick question, with the float bowls flooding like that, will it cause the engine to idle so low?

Sorry, my name is not Morph but the answer is "no"

If the floats don't stop the fuel flow, apart from the overflow mess and waste of fuel, what will happen? (apart from possible fire?)
The Bing is a three stage carb right? Runs off the idler jet at idle, the needle for midrange, and the main jet at full taps.
A full float chanber cannot have any effect on rich / lean mixture, or am I missing something?

ps. Nice illustartions [again] Greg.

Duck Rogers wrote:

Alpha wrote:Hi Morph,

Just a quick question, with the float bowls flooding like that, will it cause the engine to idle so low?

Sorry, my name is not Morph but the answer is "no"

hehe, thanks duck, but then why if the carbs are at the level they should be, and I don't rev the engine, it idles at 2050, but when I open her up and let her settle to idle, the bowls are full and she idles at 1450??

bobthebuilder wrote: The Bing is a three stage carb right? Runs off the idler jet at idle, the needle for midrange, and the main jet at full taps.

Correct, but there is some overlapping of each stage into the next but in theory, correct

A full float chamber cannot have any effect on rich / lean mixture, or am I missing something?

Nope, you're not missing anything

Alpha wrote:
hehe, thanks duck, but then why if the carbs are at the level they should be, and I don't rev the engine, it idles at 2050, but when I open her up and let her settle to idle, the bowls are full and she idles at 1450??

Haven't got a clue
This is one of those scenarios where it could be one of a few things or a multitude of things. Short of physically inspecting the installation, it's almost impossible to tell.


.......now stop fiddling

Thanks all,

I did what Morph suggested and it seems to have worked! I made the adjustments, started the engine and warmed it up for 2 minutes, i then run the engine to 4500 rpm for 2 minutes and then back to idle for 1 minute, shut it down and checked the bowls and.... Fuel level is ok. Have not flown yet as the weather is really k@k!!! So we will test on Saturday, but all things look good!

Wooooohooo... Now to stop the tinkering

bobthebuilder wrote:If the floats don't stop the fuel flow, apart from the overflow mess and waste of fuel, what will happen? (apart from possible fire?)
The Bing is a three stage carb right? Runs off the idler jet at idle, the needle for midrange, and the main jet at full taps.
A full float chanber cannot have any effect on rich / lean mixture, or am I missing something?

Won't affect the fuel mix, but.......... engine out due to insufficient fuel. The fuel literally pisses out of the overflow tubes

A quick way to check it if you have an electric fuel pump(which you should have) is switch the pump on with the engine off. If the floats are not sealing, the electric pump will push fuel out of the overflow tubes.

Hey Guys...

I'm sure the Fuel Level in the carb bowls DOES cause a mixture change ?

Higher Level ie: above 12mm fuel Level causes a Richer Mixture
Lower Level ie: below 12mm causes a Lean Mixture

Not to get too technical.....but
Higher Level - Fuel has less distance to travel up the main jet when sucked up by the vacuum and results in a richer mixture. The same is for the lower level, the fuel has further to travel up the jet and results in a a leaner mixture.

I've seen a seizure happen through low float level and Gideon Nieman confirmed this

Cheers

Some of my observations :-

Prior to starting with pre flight, I leave the mags off, and spin the prop a few times. I then put master on and fuel pump and let it run for a short while to establish flow - easiest way I've found to start this beast!

1) On one occasion , I noticed fuel on the engine mounting plate and realised the pump was still running even before I got to start it - and it looks like the excess fuel was forced out.

2) Recently, I did the above, and started, but it sounded like the choke was on, but was off. After a few times more, I noticed that the fuel pump was on, and once off, purred like a kitten.

What is the above symptomatic of ?