Zenith Carbs Massive Flooding

[Vintage56]

I had my 1971 BMW 3.0cs running very well about 3-4 weeks ago. It's been sitting due to poor weather and some work I was doing on the car. When it was started yesterday, the car started up on the second try and ran to about 1800 rpm. I blipped the accelerator pedal and it dropped down to about 1100rpm. I then noticed this massive smell of gasoline and shut the car down immediately. Upon inspection, gasoline was literally everywhere: at the top of the carbs, in the base of the air cleaner, it ran down under the car and literally had poured out onto the floor. I did not notice where exactly the fuel was pouring from as I shut it down for safety reasons. For some background, the car had been running fine. I had been fully tuned and ran perfectly after being fully warmed up. The fuel filter, fuel lines are all new and there are no cracks in them. I am thinking that something is clogged, or the float is stuck, or ? but don't want to start taking things apart until I have a game plan.

Can I get a few thoughts from everyone on what could cause this massive flooding issue? Like I said, even when it was flooding onto the floor, it ran and was responsive to depressing the accelerator pedal but I don't want to start the car again until I've done some corrections before turning the car over. Thanks for any suggestions.

 

[Stevehose]

If all hoses are intact, massive flooding like that is usually a stuck float and/or needle valve. If the carbs have been rebuilt, sometimes the top gasket needs to be trimmed to prevent the float from hanging on it. Debris in the needle valve can also keep it from closing. New needle valves in carb rebuild kits are low quality compared to the originals. Also, high fuel pressure can sometimes blow past the floats but if you are running stock mechanical pump and not an electric one I suspect this isn't the cause.

 

[Vintage56]

Thanks Steve for your response....Fuel pump is the stock mechanical one. I believe the needle valves are original to the carbs or they are "older". Should these be soaked in gasoline overnight to unclog them? I hate asking this, but can carb cleaner be used too free the float if it is hung up? How would that be done?
I am also going to tap the carbs with a light hammer.

 

[boonies]

As a temporary fix, tapping the carbs is okay if carefully done. Working with someone else, or a remote starter button, will allow you to crank the car to see if your light tapping was successful.

If the car has been sitting for any extended period in the recent past you may have deposits left by fuel breaking down. Deposits can vary from light to heavy varnish and, depending upon the fuel, could begin to attack the carburetor body leaving heavy deposits. It will be worth picking up at least a top gasket kit, if not full rebuild kits for the carbs and pulling the tops off to see what you can find.

 

[deQuincey]

Thanks Steve for your response....Fuel pump is the stock mechanical one. I believe the needle valves are original to the carbs or they are "older". Should these be soaked in gasoline overnight to unclog them? I hate asking this, but can carb cleaner be used too free the float if it is hung up? How would that be done?
I am also going to tap the carbs with a light hammer.

of course all the previous can happen, but i am reluctant to think of them if it is massive flodding

there was a story that we found common as to the loss of the small caps that block some passages in the top section, that will definitively lead to massive flodding

remove air filter and show pictures of the top of the carbs

we might be able to help.

i am unable to express myself properly in english so the descriptions might be unacurate

take pics and share them

 

[Dick Steinkamp]

I would think that if the floats were stuck with the needle valve open that it would flood internally. Very quickly the engine would stop due to too much raw fuel. I wouldn't think the engine would be responsive to the accelerator. Were both carbs wet with gas? If so, I would think it unlikely that both floats stuck open at the same time.

I'd figure out some safe way of pressurizing the lines to the carbs to check for leaks. Perhaps removing the lines at the carbs, plugging them, pull the coil wire, then have someone crank the engine over while you are under the hood with the air cleaner off to check for leaks. Someone may have not fully tightened a hose clamp or hard line fitting, maybe a line was rubbing on something and wore through, maybe a mouse in the house?

 

[deQuincey]

some literature: https://e9coupe.com/forum/threads/hunting-the-carbs-problem.8569/
i am trying to find the post on the top caps

 

[skk]

Fuel under pressure is dangerous and messy. Detach the fuel line that supplies both carbs, attach a bicycle pump, listen for leaking air. That will get you close enough to the problem.

 

[deQuincey]

found it:

Carb issue- Gas Gushing

Took MissE for a quick spin today. Running rough then stalled out half block from house. Took off air filter and filled with gas. Soaked up gas and tried to start. It started but gas was shooting out of Zeinith carb. Got back home, safe, and found this plug had blown out. Air filter filled...

e9coupe.com

look at the dangerous fuel fountain:

check this, if all ok, move onto the floats and so on

 

[Vintage56]

I would think that if the floats were stuck with the needle valve open that it would flood internally. Very quickly the engine would stop due to too much raw fuel. I wouldn't think the engine would be responsive to the accelerator. Were both carbs wet with gas? If so, I would think it unlikely that both floats stuck open at the same time.

I'd figure out some safe way of pressurizing the lines to the carbs to check for leaks. Perhaps removing the lines at the carbs, plugging them, pull the coil wire, then have someone crank the engine over while you are under the hood with the air cleaner off to check for leaks. Someone may have not fully tightened a hose clamp or hard line fitting, maybe a line was rubbing on something and wore through, maybe a mouse in the house?

Both carbs were wet but I think and can't be sure since the air cleaner was in place and I just shut it down rather than risk an explosion. I am pretty sure it's not a hose since a lot of fuel was in the base of the air filter housing and it was sealed with the clips in place. With me looking to solve this, that mouse would be named Mickey....hahahaha

 

[Dick Steinkamp]

I am pretty sure it's not a hose since a lot of fuel was in the base of the air filter housing and it was sealed with the clips in place

Good clue. It's sounding like what deQuincey has pointed out.

Do you have Weber or the original Zenith carbs? If Weber, which ones?

 

[Vintage56]

Here are the carbs AFTER I just spent 3 hours cleaning them. I don't think anything is missing. There was plenty of dirt at the top and in the throat of the carbs. I took all 4 jets out one at a time and soaked them and cleaned them as best I could before putting them back in place.

 

[Vintage56]

Good clue. It's sounding like what deQuincey has pointed out.

Do you have Weber or the original Zenith carbs? If Weber, which ones?

Zeniths

 

[deQuincey]

Zeniths

the best ones !


looking at the pics it seems that apparently all is there,
so could be the floats;

mallet tapping might make it pop and release

the solving is a little bit more messy

BTW, the fuel pump is good ? i saw a terrible flood from a fuel pump once


@Vintage56 are you dexter in zeniths ?

 

[deQuincey]

here some more info

zenith carbs rehab

doing this and that carbs come and carbs go, they get cleaner, in better shape, with new bits, and they go

e9coupe.com

 

[Vintage56]

the best ones !


looking at the pics it seems that apparently all is there,
so could be the floats;

mallet tapping might make it pop and release

the solving is a little bit more messy

BTW, the fuel pump is good ? i saw a terrible flood from a fuel pump once


@Vintage56 are you dexter in zeniths ?

The fuel pump is good. I don't think it is the fuel pump anyway since gas was inside the air cleaner and the top of the carbs....

 

[Vintage56]

I'll try starting the car again with a light hammer ready. Maybe the gas soaking the floats overnight loosened up what gunk/dirt may have hung them up. Just trying to be positive! Not sure if I am ready to work with another mess just yet.

Anything else it might be?

 

[Dick Steinkamp]

I'd do what you are planning but with a buddy in the car and you under the hood so that it can be turned off immediately if gas is shooting out. I'd also do it with the coil wire removed. Just cranking it should be enough to duplicate the problem if it still exists. In any case, have a fire extinguisher handy!

Also, if you do find it was a sticking float. I would not drive the car until the carbs have been gone through...hopefully by someone (yourself included ) who knows these carbs. You don't want the float to stick again while on a drive.

 

[Vintage56]

I'd do what you are planning but with a buddy in the car and you under the hood so that it can be turned off immediately if gas is shooting out. I'd also do it with the coil wire removed. Just cranking it should be enough to duplicate the problem if it still exists. In any case, have a fire extinguisher handy!

Also, if you do find it was a sticking float. I would not drive the car until the carbs have been gone through...hopefully by someone (yourself included ) who knows these carbs. You don't want the float to stick again while on a drive.

Hi Dick,
Good suggestions all around. I'll provide an update soon....
Thanks all.

 

[deQuincey]

I'll try starting the car again with a light hammer ready. Maybe the gas soaking the floats overnight loosened up what gunk/dirt may have hung them up. Just trying to be positive! Not sure if I am ready to work with another mess just yet.

Anything else it might be?

it is NOT " Maybe the gas soaking the floats overnight loosened up what gunk/dirt may have hung them up. "

the floats get stuck in the protruding gasket