Engine stumbles on startup

[ArtJ]

I have a late model A4 in my 1970 Tartan 34

It has been running great all season. I installed a new carb in the
spring. I have electric fuel pump. Igniter elect ignition as well as
protective dropping resistor with coil.

Yesterday, the engine started perfectly a ran for a couple of minutes
then started to stumble and died. I attempted to restart to no
avail. I tehn noticed the smell of gas and checked the throat of the
carb and it had gas dripping out of it. I also noticed gas and gas stains
in the bilge. I cleaned all of it up. Looked at the choke to see if
operating properly believe it is but could not easily look in the
barrel.
I may have 2 separate issues, can excessive gas cause flooding and a shutdown? I noticed elsewhere that someone had to replace fuel shutoff
due to a starting problem. I thought that the draft of the carb
precluded flooding? or could the choke being on cause a excess of
fuel to drip out stuck float? leaking main fuel shutoff?
the tank height causes gravity flow of fuel on the Tartan 34

Do I have 2 problems?

Comments Appreciated

Art

[Dave Neptune]

Art, there are a few ways for fuel to leak out of the throat.

First and most common would be a stuck float. Do you have filters on the fuel line?

Second and not as common is a compromised float. That is a float with a leak that can hang down leaving the needle open. This will usually cause a flood of fuel not just a leak.

Third and not so common would be lugging the engine or leaving the choke on. An updraft carb running rich, with the choke on or lugging can cause a poor fuel mix and that poorly mixed fuel will stick to the walls on the way up only to leak back down as it is liquid and not vaporized fuel.

Only in a serious over-rich situation will the excess fuel stall the engine.

Do be sure you have a good spark too.

ANY CARB MOUNTED WITH A POSSIBLE GRAVITY FEED SHOULD HAVE A FUEL SHUTOFF VALVE FOR SAFETY!!!!!!!!!!!!!!! A good place to mount the valve is on the fuel pressure gage in front of the carb.

Yes an updraft carb can flood an engine!!

Dave Neptune

[Dave Neptune]

Part II, does your scavenge tube still function? IE is the tube "clear and free of obstruction" and are the fittings tight?

Dave Neptune

[ArtJ]

Thanks Dave apreciated


I have ordered a new shutoff valve today. the original is probably 50 years

I will install it to carb.
I will recheck scavenge tube connections

I was wondering about the choke being on. I will check more carefully
tomorrow. The only thing that threw me off was the quantity of fuel and the stains in the bilge Can the choke being on cause lots of fuel to be coming
out of the carb?

. It has run perfectly till yesterday
The carb is new and new filters in the spring,

Thanks Appreciated
Art

[Dave Neptune]

Art, if the choke is on it will draw an excess of fuel that is not very atomized into the throat and a lot of it will stick to the sides only to "run down" the throat and out. It is the scavenge tube that reroutes (sucks) that fuel back into the intake manifold. If there is to much fuel the engine will flood!

Do a visual check of the choke by removing the flame arrestor.

Dave Neptune

[ArtJ]

Thanks Dave

The choke is normally spring loaded to be open I believe, but I will
check to be sure.

Much appreciated

Art

[Dave Neptune]

The choke is probably a manual cable control and not automatic. What kind of carb?

Dave Neptune

[ArtJ]

It is a manual choke. It is a zenith late model carb brand new this
spring bought here at mmi. The clamp holding the choke cable
has been making the choke tighter than before to operate last year

I need to check this tomorrow at the boat

[Al Schober]

Sounds to me like the float valve in the carb. It's supposed to shut off the fuel flow when the bowl is full. Sounds like it has a piece of grit in it that's keeping it from closing. New Carb? Then it's new grit!
I spent a few weeks (months?) one summer tracking down a similar problem. Turns out the fuel filter between the pump and the carb was corroding internally, sending rusticles into the float valve!

[ArtJ]

Thanks Al

I was tired yesterday doing some mounting of hardware and didn't go too deeply into the problem when discovered.

My initial thoughs were choke and float stuck

But was mislead by the engine shutting down like when the choke is left on too long. I believed (incorrectly?) that if the carb is over filling it was
impossible to flood the carb.

Can I try tapping the carb if stuck float or what other remedies?

The carb is difficult to remove due to very tight area I have the
scratches to prove it

I also must check the choke better as per Dave N.

Thanks

Art

[Al Schober]

Tapping the carb costs you nothing - well, if you don't hit it too hard.
How old are your filters? Does a magnet stick to them?
If you have smutz coming down your fuel lines, it's going to keep coming.
I don't think the choke is the issue.

[ArtJ]

Thanks for the input

I will start by banging the carb slightly

The filters are new in may

[Dave Neptune]

Art, a good practice is to not re-use a fuel line "end" as pulling them off of a barb often tears the inside a bit. And these bits often get stuck in the carb especially the needle & seat.

It is a good practice and not really expensive to just put on new lines to keep everything neat and clean. I would usually install my fuel lines a few inches to long then cut them off. After cutting I would have a "fresh" end to deal with.

I'd install a pressure gage while at it. Can really aid in diagnostics.

Dave Neptune

[jcwright]

Hello Artj.

As a fellow Tartan 34 owner, one of your comments got my attention, namely, that the carb is difficult to remove due to the very tight engine compartment.

I agree that there isn’t much room between the carb and the battery compartment. But in my experience at least, the main “knuckle scratcher” is detaching the scavenge tube. The fuel line, throttle, and choke cables are more accessible. My recollection is that it helps to remove the flame arrestor before moving the carb down and forward.

Of course, if you have an oil or fuel filter mounted across from the carb, access would be worse.

best regards,

Jack

[romantic comedy]

I find that the carb is easy to remove on my T34.

Sounds like a stuck open float valve.

Why did you get a new carb? This is often a big clue.

Also the choke cable may need to be lubed.