Blankety-Blank Carb still leaking . . . .

rivcokid

rivcokid

Senior Member
'm about ready to chuck the carb on my 1931 town sedan

For months it's been giving me issues, and I've been chasing them down. In essence, the car kept wanting to die when I slowed down/stopped. Once I stopped, it idled beautifully and ran beautifully too, except when I'd slow down. I've tried all the normal issues - jets, float level, throttle screw, idle adjustment screw, etc. I've finally found what appears to be the real, underlying issue - it's been getting too much gas thanks to a leaky GAV needle (note also that the plugs were covered in carbon).

So, I took the needle assembly out (2 day job, don't ask). I replaced it with a new one (shaft and needle) per the instructions on the Paul Shinn video about rebuilding a zenith carb, and voila! The car was running fine. HOWEVER, it's now leaking more gas than before through the GAV. In fact, when I drove it this morning, the GAV was completely closed and it ran fine, although there's still a little hesitancy when slowing down. When I parked it in the garage and let it sit for a while, the GAV was wet as was the bottom of the carb.

So, once again, I'm appealing to you folks. What the ^$** am I missing now? Is there a plug or something that is supposed to be at the end of the needle? There's certainly no place for one. Is there something else that is supposed to be in there? The passageways are clear throughout the carb (if they weren't, I'd guess that the car was getting too little gas - this one is still getting too much gas).

I'd appreciate any ideas at this point. Thanks for your time!!
 
The threads in the carb body that the GAV needle housing screws into might be boogered up. They are supposed to be a NPT tapered thread so that as you screw the housing in the threads lock and seal before it bottoms out. Someone in the past might have chased those threads with a straight tap. You might try applying some gas-resistant thread sealer on the threads, but I might look for a replacement lower body at the next swap meet you go to.
 
rivcokid said:
'm about ready to chuck the carb on my 1931 town sedan

For months it's been giving me issues, and I've been chasing them down. In essence, the car kept wanting to die when I slowed down/stopped. Once I stopped, it idled beautifully and ran beautifully too, except when I'd slow down. I've tried all the normal issues - jets, float level, throttle screw, idle adjustment screw, etc. I've finally found what appears to be the real, underlying issue - it's been getting too much gas thanks to a leaky GAV needle (note also that the plugs were covered in carbon).

So, I took the needle assembly out (2 day job, don't ask). I replaced it with a new one (shaft and needle) per the instructions on the Paul Shinn video about rebuilding a zenith carb, and voila! The car was running fine. HOWEVER, it's now leaking more gas than before through the GAV. In fact, when I drove it this morning, the GAV was completely closed and it ran fine, although there's still a little hesitancy when slowing down. When I parked it in the garage and let it sit for a while, the GAV was wet as was the bottom of the carb.

So, once again, I'm appealing to you folks. What the ^$** am I missing now? Is there a plug or something that is supposed to be at the end of the needle? There's certainly no place for one. Is there something else that is supposed to be in there? The passageways are clear throughout the carb (if they weren't, I'd guess that the car was getting too little gas - this one is still getting too much gas).

I'd appreciate any ideas at this point. Thanks for your time!!
Click to expand...
all jets one washer only!! Have to look in there to see if old ones exist. Idle Jet NO washer. And they are tight!
 

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Hello rivcokid, I can understand your frustration with the stalling problem. It is time to take a deep breath, relax and if you are tired, put off further investigation till tomorrow! I have rebuilt carburetors for my club and encounter this problem often. I have come to the conclusion that this stalling problem is a Ford design problem. Look at the orientation of the Model A float hinge. The 1932 Model B float hinge is rotated 90 degrees from the Model A orientation. This is what happens when you step on the brakes. The gas in the carb bowl surges forward. This will lift the float and shut off the supply of gas to the carb. Also, the gas flow to the main jet will stop because the throttle plate goes closed, removing the vacuum that has been lifting gas out of the Main Jet. (the Main Jet is one of the jets in the throat of the carb.) The other jet (Cap Jet) is not furnishing gas at this time for two reasons: 1) there is no vacuum, same situation as with the main jet, and 2) the Cap Jet is not furnishing much gas because its source is the Secondary Well and at this moment, the Compensator Jet which fills the Secondary Well may not be covered with gas due to the forward surging gas in the bowl. 3) The gas level in the bowl may go low . The only potential source of gas from the carb to the engine is the Idle Jet but its source of gas is also from the Secondary Well and it is low or empty of gas. Now you have a race between filling the Secondary Well in time before the engine stalls from going lean from insufficient gas.

It surprises me that Ford was able to ignore this stalling problem for four years. So, the big question is what to do?
1. As you approach a stop sign, slightly pull down the throttle lever to increase the engine speed so you can avoid the stall. This has to be done as you are lifting your foot off of the accelerator. This action will prevent a stall because you are opening the Thottle Plate slightly to re-introduce vacuum to the Main Jet. I don't like to do this because it it is another action that has to be done when you are trying to stop the car.
2. I try to reduce the time it takes to refill the Secondary Well. The Compensator Jet fills the Secondary Well but as the gas goes through the Compensator Jet it meets the wall of the Secondary Well, flows down the outside wall of the Secondary Well and into the tiny holes at the bottom of the Secondary Well. Make sure these tiny holes are open. I have been putting a groove in the wall of the Secondary Well with a Dremel Tool, starting at behind the Compensator Jet down to the bottom of the Secondary Well where the tiny holes are located to increase the gas flow rate to the Secondary Well. 4) Make sure your float level is adjusted properly to the 5/8 in. setting. You might try increasing the level 1/16 in. higher to put more gas into the bowl but this usually leads to leakage out of the Main and Cap Jets.

You mention that your GAV is now leaking. This should shutoff tight because the GAV is a bypass around the Main Jet to provide extra gas on a cold start and also as a supplement to the Main Jet if extra gas is needed for more power. If it is leaking, it will make the engine run rich, therefore resulting in a dark, carbon tail pipe.

Make sure the jets in your carburetor are correctly sized so that the carb can provide the correct air/fuel ratio through-out the speed range. From my experience, I would recommend the following jet sizes:

Main Jet - 153 ml/min. (Do a flow test over 1 min. using a graduated cylinder). This is an economy setting and will provide a light grey tail pipe.
Idle Jet - 40 ml/min.
Compensator Jet - 140 ml/min.
Cap Jet - 175 ml/min.

Do not expect to get proper jet sizing without testing. See carb rebuilding manuals for how to make your own jet sizing equipment. Do not rely solely on using drill sizes to make the correct size jet holes. Jets should be tested for correct flow rates.

Sorry to be so wordy! Unfortunately, getting a good operating carb can be tricky. But, if the carb is clean, jets are properly sized and float level is proper, good results can be obtained. Good luck, Ed
 
rivcokid said:
'm about ready to chuck the carb on my 1931 town sedan

For months it's been giving me issues, and I've been chasing them down. In essence, the car kept wanting to die when I slowed down/stopped. Once I stopped, it idled beautifully and ran beautifully too, except when I'd slow down. I've tried all the normal issues - jets, float level, throttle screw, idle adjustment screw, etc. I've finally found what appears to be the real, underlying issue - it's been getting too much gas thanks to a leaky GAV needle (note also that the plugs were covered in carbon).

So, I took the needle assembly out (2 day job, don't ask). I replaced it with a new one (shaft and needle) per the instructions on the Paul Shinn video about rebuilding a zenith carb, and voila! The car was running fine. HOWEVER, it's now leaking more gas than before through the GAV. In fact, when I drove it this morning, the GAV was completely closed and it ran fine, although there's still a little hesitancy when slowing down. When I parked it in the garage and let it sit for a while, the GAV was wet as was the bottom of the carb.

So, once again, I'm appealing to you folks. What the ^$** am I missing now? Is there a plug or something that is supposed to be at the end of the needle? There's certainly no place for one. Is there something else that is supposed to be in there? The passageways are clear throughout the carb (if they weren't, I'd guess that the car was getting too little gas - this one is still getting too much gas).

I'd appreciate any ideas at this point. Thanks for your time!!
Click to expand...
send to me and i will fix for postage only!
 

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@Ed in Maine - thanks so much for taking the time to send me a lot of great information. I will try those and probably invest in a set of jets that have been flow tested. Regardless, I'm going to keep the information right at hand!

@Gary WA - Wow - that is very kind of you. Thanks for the offer. I may just take you up on that!
 
Rivco
I tried a different comp jet years ago, and I haven't had the stalling problem since. I don't remember whether the orifice was much larger than the one I had, but my logic was, if the secondary well is running out of gas(my guess) I'll just refill it faster. I think I read that this affects mileage, but I get around 17-19 every tank(GAV completely closed 95% of the time), and I'm satisfied with that. It's a cheap and easy try. Just buy one and drill it a little bigger than your present one, if necessary re-drill it again, and again.
 
@28phaetonroy - Hmmmm. Hadn't heard that one yet. It's certainly worth a try. Thanks!!

I'm at a point right now that I seem to be making it better incrementally. I put another shim in the inlet valve, and it improved the situation somewhat. Not nearly enough, but it is better than it was. Now if i can just maintain it . . . . .

Thanks again everyone!!!
 
rivco
Out of curiosity, while I had my carb apart today to fix a leaky float valve, I looked at the comp jet. It has a 19 marked on it. Somewhere I have an explanation of what the jet numbers mean, but don't know exactly where right now.

While I had things apart, I put a slightly thicker gasket under my viton tipped float valve to lower the fuel level a little because the bottom of my carb stays damp with gas lately. The float is now perfectly parallel with the carb body when held upside down. After blowing everything out the float valve has stopped dripping, so it must have had dirt in it.

A test drive performed A-ok.
 
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