Carburetor question

F

Forddan

Senior Member
Hi

I will start saying I am new on model A so my knowledge is more than basic. I will appreciate if I can get some guide on this issue.

The carburetor gasket and air filter were changed a couple of weeks ago. After that I started to have some engine stalling at traffic lights. Yesterday I drove 30 miles to a club event (60 miles round trip). Going to the event all was fine. At the return I have an engine stall at a traffic light and arriving home at a soft street slop (front of the car up in the slop).

I decided to try to adjust the idle. Followed what technical books said.

I was not being successful at all, with black smoke out of the exhaust. Then suddenly I found a sweet spot where the car was idling nice when I had the dash control 1/4 open. Drove to the gas station. Filled the tank. I asked the gas station guy to look the exhaust when I accelerate. He said that a small amount of black smoke where still produced.

Then suddenly the car started to shake, front to back, like if the engine was stopping/starting. But I can only feel the shaking. Stopped and I saw the carburetor leaking gas, drop after drop significantly faster. Put the firextinguisher beside me and drove back home.

Any idea / suggestions of what I did incorrectly?

Thanks!
Daniel
 
Last edited:
My answer to a question like that is to remove the carburetor and rebuild. Either you do it or have a guy that knows Model A's do it for you. Someone in your club must know someone that can rebuild it. Good luck. Jack
 
I would remove the float valve assembly and remove any trash that could prevent the needle from setting in the float valve seat . As always , I replace the float valve gasket any time that the float valve is removed and replaced . Check the float for leaks . Shake the float and feel for gas that could be inside the float . The float setting is suppose to be 5/8 . I usually set my float so as to lower the fuel in the bowl of the carburetor a small amount more to prevent stalling when braking or coming to a quick stop .
 
Probably a leaky inlet valve - very common. Do a little homework and rebuild the carb. They are very simple and normally require only a new inlet valve and a few gaskets to redo. Be sure to blow out all the passages, especially the idle circuit, with carb cleaner. No shortage of advice if you need it. Good Luck.
 
Last edited:
To check that level function you'll need to make a specialized tool - or have a REAL steady hand as you hold a cup under the float and valve with the lower carburetor half removed.

The usual tool uses a short length of tubing and a connection to the lower drain plug. I've done this with a longer tube and holding the tube up to the side of the carburetor for better eyeball. (liquid seeks its own level irrespective of the tube.)

One video addresses the "mechanics" of the 5/8". He is correct in generalities but his 5/8 measure is to the float and not the actual level. Might work for you as it has worked for me. https://www.youtube.com/watch?v=WwRZCws8EeQ

Our Tom Endy has addressed the issue more forwardly - and perhaps more accurately using the "auxiliary cup" method. http://www.santaanitaas.org/wp-content/uploads/2014/08/Zenith-Float-Valves.pdf

Hope this helps. It actually sounds like a mere cleaning might work alone - but while you're in there you might as well...

The story of the Model A.


Joe K
 
Good Morning all...Since our Model 'A's have a hand throttle, I always have my hand on it when I come to a light or a stop sign. I rarely have to advance the hand throttle to keep the engine running...but once in a while with a quick stop! Usually, I just advance the throttle for a couple of seconds and then put it back up. If the problem happens with any regularity, then a clean out or rebuild of the carburetor is definitely required. Ernie in Arizona
 
If it happens again, or is continuing to happen, once in a while the float valve may not seat properly causing gas to overflow out through the air intake. Sometimes tapping the float bowl with a hammer or wrench is enough to get the float valve to seat.


If tapping does not stop the leak, or it happens frequently, then additional troubleshooting above is needed.


Until you resolve this issue, do not run with the air filter on. Getting gas in the air filter is not a good thing.
 
Sounds like maybe 2 issues. Like Purdy mentioned, lowering the fuel level just tad [ 1/16"] to help with the stall upon stopping.
While apart checking things, the float should be checked for fuel infiltration as mentioned, passages blown clear and float valve checked or replaced. Its a very simple carburetor.
 
What kind of air filter are you using. If it is a paper pleated, take it off and throw it away. The commercial paper filters sold by the Model A vendors are not adequately sized for an adequate air flow for the Model A ford engine.

http://www.model-a.org/filtering_air_into_carb.html

The calculation on the web site are at an engine running 2800 rpm, and the conclusion is you can use any one of three filters, they conclude any of the three filters below are adequately sized.
◦K&N offers several filters that can be used with the Air Maze housing.
◾Part # E-3050 is 3.5 inches long.
◾Part # E-9257 is 5.5 inches long.
◾Part # E-2040 is 6.625 inches long.
But the site make this recommendation.
“◦To provide some margin for the filter getting dirty, before you get around to cleaning it, I would recommend the 5.5 inch long length. I know it is an over kill, but I am currently using the 6.625 inch long one to allow for driving on dusty gravel roads and to extend my time between filter cleaning / re-oiling cycles.”


I agree that if you put an air filter on a vehicle that is not rated at the CFM per minute of air flow that the engine requires to run at performance RPM you will have an engine that runs rich and fouls plugs. The paper filters that are offered by some vendors to fit the air maze filter housing do not have any CFM rating, they just happen to be the right size, and they will restrict air flow and result in fouled spark plugs!!
 
Wow... you all are fantastic. Thank you for all the info. A lot to learn.

One of my club members offered to do a full service to the carburetor. I took it out following the mechanics book indication and tomorrow will be in his hands. When ready he offered to bring it home to install it and regulate it.

I have other hobbies, but you Model A fans are such nice persons. I always wanted an antique. At 61 I was able to get my model A.

I will never regret my decision. The A's are great easy cars to maintain and you find everything. BUT, THE MOST IMPORTANT......The A's people !!! That is what keep a hobby alive.

As soon as my club friend tell me what he found and did, I will post back.

Cheers !!
Daniel

Ah... and I will trash the paper air filter the vendor sold me. Previously had a metallic one that I cleaned and kept just in case.
 
Last edited:
The club member that offered to check my carburetor sent this :

I have taken the carburetor apart and have the following observations:

The most obvious item I found was a missing gasket under the float valve. This is important and may have been the root cause of the leaking. Other items checked and fixed in no important order are the following:

Throttle shaft binding (repaired)

Idle Air screw not closing off air (replaced with one of mine)

All gaskets under the jets and bowl gasket replaced with new ones

The GAV needle and housing was binding a little (repaired)

Float was not set perfect and float was binding in float hinge (repaired and reset float) Also, tapped and cleaned threads

Cap jet was loose (repaired)

Gas inlet seat (where fuel line comes in) needed to be cleaned with Dremel stone (repaired), tapped and cleaned threads

Inspected all jets to make sure they were open and without any rust clogging

Cleaned secondary well thread area (had rust inside)

Inspected fuel passages with high intensity light to check for blockages (found nothing)



On top of all that, he will come to install it and check all is doing well.

Incredible nice guy !!!
 
You must log in or register to reply here.
Back
Top