Needle & Seat - Now with some real data!!

[29 Tudor]

Hi all,

I have a '29 with a stock Zenith on it. Periodically, (worse in in HOT weather) when climbing a light hill, it will act like it's running out of fuel. New line, new kit in the stock cast iron filter and it has GOOD flow out of the line at the carb. I pulled the carb apart and it has one of the old needles in it that is captured in the seat by a metal bar across the top (or bottom, depending on how you look at it) of the seat assembly. I was surprised to find that the drop of the needle is only about .025. I can BARELY feel any air when I blow through it. I'm sure that has a lot to do with the starving problem.

In looking at the various web sites for "A" parts, it looks like all the vendors are featuring the "Grose type" inlet assembly. I have read of a number of sticking problems with that design and would really be happy to find a good, HIGH FLOWING needle and seat. Does anyone still make a traditional needle and seat assembly for the old Zenith?

If not, I will have to try to disassemble the needle and seat I have and relieve the stop bar to get more, MUCH more drop on the needle.

Frankly, I'm amazed it runs as well as it does with no more drop than it has on the needle. There CAN'T be much flow through there.

Any thoughts out there?

Thanks,

Steve

[BRENT in 10-uh-C]

Steve, if you want to explore, remove the "cage" from the seat and see what you find. It is very possible the Viton material on the needle point is damaged or swelled restricting the flow. Maybe something can be fixed after opening up but realistically you have nothing to lose. I will tell you that a high-flowing Needle & Seat really is unnecessary in 99.9% of the applications you would ever bolt that carb on. It just doesn't take that much fuel to adequately supply the engine's needs.

As far as the Grose-Jet is concerned, Bill Stipe makes the best ones now. Several years ago there were some Chinese manufactured ones that did stick and give issues but I don't know of Bill having any of those issues with the ones he makes.

One other possibility would be to call Bill Coleman over in the Channelview area and see if he would have a core carburetor that would have a decent brass "original style" Needle & Seat that you could install in your carb.

.

[29 Tudor]

Hi Brent,

Thanks for the comments. I am going to do a flow test on the open line and then through the needle and seat and see what I find. I was surprised how little drop there was in the needle so it's probably good to see what that really does to fuel flow.

When I pull a "hill" (if you can call them that here in central Florida), it will typically pull well part way up the grade and then start to act like it's running out of gas. If I let off the throttle, it comes back and pulls again and then when I go full throttle, in a short while, it will starve again. I'm sure there is plenty of flow TO the carb so I suspect it has to be the restriction of the needle/seat but I'll report the flow results.

Thanks again for the thoughts and comments.

Steve

[cars56]

Amazing how much impact jets that are not factory impacts performance.
Solder them shut drill em out, makes a huge difference

[29 Tudor]

I have no reason to believe I don't have factory jets in this carb. In fact, the mixture control works as expected so I would be surprised to find the jet is wrong. The car runs excellent other that the full throttle performance on grades.

[flatford39]

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When you "pulled that hill" did you have a full tank of gas? If it was a quarter tank or less you may have had a problem with the gravity fuel delivery system that our A's have. I was told it was common practice to go up hills in reverse when the tank was low.

[29 Tudor]

Great suggestion but... I thought of that and tried it with about 1/4 tank and then about 3/4 tank. It made a SLIGHT difference but still happened with 3/4 tank of fuel.

Great thought though. Thanks for suggesting it!

Steve

[Pilotdave]

Originally Posted by flatford39

When you "pulled that hill" did you have a full tank of gas? If it was a quarter tank or less you may have had a problem with the gravity fuel delivery system that our A's have. I was told it was common practice to go up hills in reverse when the tank was low.

With outlet positioned as it is, would there be an issue with fuel flow from the tank going up hill?

[Kurt in NJ]

I thought it was with "T" that had the fuel tank under the seat that steep hills caused fuel flow problems.

[1931 flamingo]

Does the carb "open" all the way??
Paul in CT

[29 Tudor]

Yup, checked that too but if it wasn't, opening it more would only aggravate the problem. Thanks for the thought though.

Steve

[29 Tudor]

Okay, here's some data and some math....

I started with 1/2 tank of fuel. I took the line off the carb and measured the flow of fuel into a quart container. It took 50 seconds to get a quart or 200 sec/gal. That's obviously 20 seconds/0.1 gallon.

Next, I measured the flow out of the drain on the carb. It took 180 seconds to get a quart or 720 seconds/gallon. That's 72 seconds/0.1 gallon.

Now, I don't know what mileage an "A" gets at full throttle while pulling a grade but I'd guess it's between 5 and 10 MPG. So, that being said, if it's 10 MPG, we need 0.1 gal/mile. That means that at 30 MPH, we need 0.1 gal/120 seconds.

If it is getting 5 MPG, we need 0.2 gal/mile and at 30 MPH, we need 0.2 gal/120 seconds or 0.1 gal/min.

As you can see above, I'm only getting 0.1 gal in 72 seconds so, assuming my mileage estimate is anywhere near accurate, my needle will not flow enough fuel to support the motor at full throttle and it's simply running out of gas.

Now I need to see what I can do to increase the flow through the needle & seat... or build a better mousetrap.

Steve

[Farrell In Vancouver]

Originally Posted by 29 Tudor

Hi Brent,

Thanks for the comments. I am going to do a flow test on the open line and then through the needle and seat and see what I find. I was surprised how little drop there was in the needle so it's probably good to see what that really does to fuel flow.

When I pull a "hill" (if you can call them that here in central Florida), it will typically pull well part way up the grade and then start to act like it's running out of gas. If I let off the throttle, it comes back and pulls again and then when I go full throttle, in a short while, it will starve again. I'm sure there is plenty of flow TO the carb so I suspect it has to be the restriction of the needle/seat but I'll report the flow results.

Thanks again for the thoughts and comments.

Steve

Steve, this might be completely wrong, (probably is) but have you considered the engine might be running too rich at full throttle?
I only mention this because you said it comes back when you let off the gas. How does the car perforn full throttle on the flat highway?
Are you experiencing and lean back firing or is it loading the plugs?
Perhaps you could find a spot halfway up that hill chop the ignition, pull over, read the plugs and see what is happening. After disassembling a few carbs, I have found many jets too be "improved" by someone before. Worth a shot?
Interesting flow test you performed on the carb. I wonder if the time/flow difference was due to the fuel being slowed by the float seat and the bowl on its way to the quart jug.
Good luck friend, I am eagerly waiting for your solve on this problem.

[gweilbaker]

Steve,
The drain you refer to, is it the cap for the main jet also? If so, I would check a few things before heading to the trap store.

- Check the fuel line that it is not set too deep per the ferrule, like the line bottoming in the boss and a good length of line showing past the ferrule.

- How's the strainer screen?

- Make sure the in put path is clean and not obstructed with varnish, rust, crud, teflon tape or an old strainer. I have found all the above before.

Good luck,
GW

[29 Tudor]

Farrell:
I don't think it's running too rich... If I lean it with the GAV, it will clearly start to fall off so I have it on the "sweet spot". I also fly a plane (172) so I have experience leaning the motor. It runs well on flat ground and I have not held it at full throttle for a long period because I really don't want to rev it that high but on a couple of occasions at about 45 MPH or so, it has acted like it is trying to starve as well.

With the VERY tiny drop I get with this needle, (~.025) I do believe it's a significant restriction and with a little machine work, I can address that.

gweilbaker:
The drain I am referring to is the drain on the bottom of the Zenith bowl. It is a gasketed "bolt" that goes only into the bottom of the bowl. This carb looks new inside and out and is VERY clean.

I will check for bottoming of the line... that's a good point. I'll probably remove the needle and seat and redo the flow test. The line is new as is the filter in the cast iron sediment filter on the firewall. If there was a problem with the line to the carb or the filter, I don't think I would be getting the flow I am out of the open line at the carb. I think a gallon in 200 seconds will support a lot more horsepower than a basically stock "A" can make.

I do appreciate the thoughts and comments. Unfortunately, I will not have resolution to this soon as I am about to have to set this project aside for a while but I WILL get this solved... and when I do, I'll update this thread with the results.

Steve

[John S]

Sent a PM to you, Steve

[29 Tudor]

Hi John,

Sent one back....

[Purdy Swoft]

It sounds like you may be running a Simmons or Wizard improved cast iron carburetor. The original type Zenith carbs didn't have a drain under the bowl. The Simmons and Wizard carbs did look a lot like the original carbs and even produced a side bowl for the 31 models. All of the above carbs did have a bolt-plug under the main jet, just behind the bolt that holds the two halves of the carb together and this may be the drain that you refer to.

Here is a few thoughts about what could be causing the problem, incorrect float setting, add on fuel filters, micro filters, or any of the good suggestions that others have already given.

[29 Tudor]

You probably have more experience with the Zenith carbs than I do but this one has "Zenith 1" in the side of the cast iron bowl and the drain I refer to goes in a boss that is machined on the bottom of the bowl, next to the single bolt that holds the carb together. It looks just like Bratton's part number 14590 which is called "CARBURETOR LOWER DRAIN PLUG"

There are no add on fuel filters, the line is brand new (I just installed it). Also, as noted above, the flow FROM the line at the carb is good. It will flow a gallon in 200 seconds from a tank that is 1/2 full.

Thanks for the thoughts,

Steve

[Jim/GA]

Originally Posted by 29 Tudor

You probably have more experience with the Zenith carbs than I do but this one has "Zenith 1" in the side of the cast iron bowl and the drain I refer to goes in a boss that is machined on the bottom of the bowl, next to the single bolt that holds the carb together. It looks just like Bratton's part number 14590 which is called "CARBURETOR LOWER DRAIN PLUG"

There are no add on fuel filters, the line is brand new (I just installed it). Also, as noted above, the flow FROM the line at the carb is good. It will flow a gallon in 200 seconds from a tank that is 1/2 full.

Thanks for the thoughts,

Steve

The drain you are opening for your flow test is under the main jet. I do not believe that there is any other restriction between the fuel bowl and this drain plug, but it has been a while since I looked at it. I would say that this is a fair flow test.

I have also noticed that these needle valves do not drop very much. I always considered them to drop enough to run the engine, though.

What are you doing with your spark advance as you climb this hill at WOT? Did you ever try enriching the mixture with the GAV, not leaning it? You are asking for a lot of power.

[quickchange]

Have you tried flow with fuel cap off??? as sometimes the air vent can get restricted alowing flow for most but under load will restict. Just a thought & once you find the problem let us all know, Derek from a frosty NZ

[29 Tudor]

Jim/TX:
I have tried retarding the spark a bit but it seems to make little if any difference. Of course, if I go too far, the power falls way off. At cruise, she seems to be happiest with the spark most of the way advanced. I have also tried opening the GAV a bit but, as might be expected, it seems to make the symptoms a bit worse and somewhat slower to recover. That might just be perception though as once it happens, its recovery is very predictable.

I'm going to pull the needle/seat completely out today and do the flow test again, just to be satisfied that nothing else is contributing to the problem.

quickchange:
Great thought on the fuel cap... that was one of my first thoughts as well. My cap LOOKS good but to be sure, I reached under the windshield and removed the cap when it started and it made NO difference in the symptoms at all. Then I drove with it off and (other than the gas smell) the problem occurred in exactly the same manner.

Thanks to both of you for the thoughts.

[29 Tudor]

Here's some more information:

I pulled the carb again (LOVE these simple things to work on!!!)and found that as suggested above, the drain plug is in fact, the access for the main jet and is not directly under the bowl. Pulling it does drain the bowl almost completely but it is through a passage that is roughly .125 inch in diameter. In order to be sure about the flow, I redid the tests I had performed before by leaving the bowl assembly off the carb and measuring the flow through the needle and seat with no float installed at all.

As before, the numbers were virtually the same with it taking 180 seconds to get a quart through the needle and seat. I then pulled the needle and seat assembly completely out of the carb to verify that there was no undue restriction at the end of the inlet fuel line and ferrule or through the in-carb filter, located behind the inlet port. Again, the numbers came out surprisingly close to the original numbers at 50 seconds to get a quart. By the way, there is a boss that prevents the fuel line from going in too far and getting blocked.

I did one more test to check the flow rate of the passage to the drain below the main jet by leaving the needle and seat out and putting the bowl back on. I turned the fuel back on and the flow out the “drain” was considerably diminished and in fact, in a few seconds, fuel started flowing out the vent at the top of the bowl. Therefore, it’s quite possible that measuring the flow through the needle and seat by using the drain plug is not, in fact completely accurate. However, by redoing the test with the bowl removed, I have no doubt about the absolute flow.

With that, I’m pretty convinced that the problem I have is related to low flow through my existing needle and seat. It will be a while before I get the new parts and get back to this but once I do. I will report on the results.


Thanks again to all who have commented and offered suggestions.


Steve

[John S]

Good Deal!

[29 Tudor]

Hi John,

I wanted to be SURE I had the data I needed and I'm convinced now that I don't have enough flow. I have ordered a couple of new inlet valves (two different styles) from Mac's so when I get back to the car, I bet I can get it fixed, once and for all.

Thanks again for your help,

Steve

[gweilbaker]

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Steve,
For Grins and giggles until the new parts arrive, what kind of flow rate do you get without the float valve body? Of course without the bottom half of the carb.

GW

[29 Tudor]

Unless I misunderstand your question, that's what I reported above. With no float valve (needle and seat) in the upper body and with the bowl (lower body) off, it takes 50 seconds to flow a quart through the upper body and into a quart jar. I was surprised that it was the same number I got out of the open fuel line. I had expected some restriction through the in-carb filter but that was not the case.

Steve

[gweilbaker]

WOW! I did not see that post. I think I was on the site earlier, returning after a few meetings then submitting my post before refreshing the site.

Sorry,
GW

[29 Tudor]

qweilbaker:

No problem! I thought maybe I misunderstood your question. You need to stop going to meetings!<grin>

.... retirement is great!

Steve

[29 Tudor]

Well, I got back to the car today and I have some NEW data!!!

As you might remember, with the needle and seat that I suspected was bad, it took 180 seconds to flow 1 quart of gas through the needle and seat. Today I installed a new "Viton" needle and seat from Mac's and did the same test again. This time, it took 75 seconds to get 1 quart through the new needle and seat. That results in 300 seconds to get a gallon, or 30 seconds to get 0.1 gallon.

As I reasoned before, if a Model A gets 5 MPG under full throttle, it needs 0.2 gal/mile so at 30 MPH, we need 0.2 gal/120 seconds or 0.1 gal/60 seconds. Clearly now, I am getting TWICE the maximum flow I would need if the car is getting 5 MPG.

This testing was done with only 2.5 gallons of gas in the tank since I emptied the tank (DRY!) to pull the gas gauge and overhaul that.

Hopefully this data will help someone else troubleshoot a fuel problem.

Driving the car now results in MUCH better operation under large throttle settings. It does have a new symptom that I need to work on and that is that it is running lean. Even with the GAV open 3-4 turns, it seems to starve and pulling the choke slightly results in MUCH more power but with the choke partially on, it now climbs the "hills" and never runs out of gas. MUCH better than before.

Tomorrow I'll verify timing and pull the carb again and look for some restriction in the jets as well as verify the fuel level.

[Purdy Swoft]

I'm going to guess that you've got a vacume leak. My thought is weak vacume is not allowing the engine to draw the fuel. When the choke is partially applied it increases the draw through the carburetor and the engine gets more of the needed fuel supply. I would check gaskets. I use the copper clad gasket between the carb and intake. It could be a small crack in the intake manifold or upper carburetor housing. The gaskets between the manifold and engine block could be leaking vacume at the intake manifold ports. If you are using vacume windshield wipers, there could be a vacume leak somewhere between the manifold and the wiper motor, or the wiper motor itself. Good luck with your search for the problem.

[29 Tudor]

I suspected a vacuum leak as well but inspection today didn't disclose one. I'll get deeper into it tomorrow. Thanks for the suggestion.

Steve

[Jerry in Shasta]

Could this be vapor lock.
JB

[Ron in Quincy]

Using a torch tip cleaner, mic the smooth end and hopefully you will come up with tips measuring .021, .037, and .039.

Make sure your idle jet is .021 ; make sure you have a type 3 removable secondary well (the one with the undercut at the entrance of the compensator jet).

Compensator jet: .037
Main Jet: .037
Cap Jet: .039 ( this will give extra fuel when excelerating.

When climbing a long hill, open needle seat 1/4 turn and slightly retard dristributor.

Also make sure you do not have the float level too low. If you get it too high it will run over the top of the cap and main jets. Sometimes you need to add a second gasket under the cap jet so it is at the same height as the main jet.

Ron

[29 Tudor]

Jerry, I wouldn't think vapor lock since the choke helps it. If it was out of gas (as with the old needle and seat or vapor lock), I wouldn't expect the choke to help it.

Ron, Thanks for the jet sizes. I doubt that's it since this carb ran fine before (until it became fuel-limited) but that's great info to have and it's on the list to check.

I appreciate it!!

Steve

[Tom Wesenberg]

Jerry might be right. That was my first thought when you said it is worse when hot. If I use crap gas with 10% corn squeezins then it acts the same way if the temps are over 80*. As soon as I switched to the regular good gas the problems went away.

[George Miller]

Originally Posted by 29 Tudor

Hi all,

I have a '29 with a stock Zenith on it. Periodically, (worse in in HOT weather) when climbing a light hill, it will act like it's running out of fuel. New line, new kit in the stock cast iron filter and it has GOOD flow out of the line at the carb. I pulled the carb apart and it has one of the old needles in it that is captured in the seat by a metal bar across the top (or bottom, depending on how you look at it) of the seat assembly. I was surprised to find that the drop of the needle is only about .025. I can BARELY feel any air when I blow through it. I'm sure that has a lot to do with the starving problem.

In looking at the various web sites for "A" parts, it looks like all the vendors are featuring the "Grose type" inlet assembly. I have read of a number of sticking problems with that design and would really be happy to find a good, HIGH FLOWING needle and seat. Does anyone still make a traditional needle and seat assembly for the old Zenith?

If not, I will have to try to disassemble the needle and seat I have and relieve the stop bar to get more, MUCH more drop on the needle.

Frankly, I'm amazed it runs as well as it does with no more drop than it has on the needle. There CAN'T be much flow through there.

Any thoughts out there?

Thanks,

Steve

Are you sure it is a gas problem and not a weak spark? Have you tried pulling the choke a little to see if it gets better when it does miss.

[kenparker]

Experiencing a similar problem with 'le Coupe. Pulled the Screen out of the front of the carb yesterday and discovered the screen plugged with varnish. Blame it on sitting for extended periods of time (30 days at time) and this confounded ethey nol gasolene. Moral of story - check your screen. ken

[29 Tudor]

Tom: I have little doubt that the gas we have now is compounding the problem and I would LOVE to be able to get "real" gas but all we have here is the crummy gas. I sure wish they would leave the alcohol to Jack Daniel's!

George: Yes, I have tried pulling on the choke (slightly) and it helps considerably. By the way, the problem does not manifest itself by missing, the power just falls off and it helped considerably by applying a little choke.

Kenparker: It's not the screen... at the bottom of the post I posted the new data with the new needle and seat. It will now flow twice the fuel I calculated was needed at full power.

I have attacked the problem in several ways; I checked the timing and found it to be a little retarded (probably about 10 degrees) from where it was supposed to be so that is now corrected. I pulled the carb off and disassembled it to check all the jets for size (they were all correct) and obstructions and found them all to be perfectly clean. While reassembling the carb, I snapped off the Cap Jet so I have ordered a new one along with the required tap to remove the broken part. I have a spare (professionally rebuilt) carb that I intend to put on the car hopefully in the next few days.

The old carb to manifold gasket was pretty flat so the new carb will go on with a new gasket. I hope the new carb and gasket along with the timing being corrected will fix the problem. I'll report as soon as I get it back together.

Thanks to all for the suggestions!

Steve

[George Miller]

If the choke helped then it is a gas problem for sure.

[29 Tudor]

Hi George,

That's my thought as well. Hopefully, the new carb and new gaskets will fix the problem.

Thanks!

Steve

[29 Tudor]

Here's the latest.....

Rebuilt carb and timing set correctly and the car runs fine... until the crummy gas we get now starts to boil in the carburetor. When cool, the car runs great. If I have to sit in traffic for a while, it runs poorly until the carb gets filled with cool(er) fuel. I stopped at the grocery store with the wife and shut her down and opened the hood. I could actually feel the fuel boiling in the carb. (It was 86 degrees outside, here in Central Florida) The Motometer was below the bottom and the fuel line and carb were cool enough to hold my hand on but there was no doubt the fuel was boiling!

I suspect I will just have to live with this although I am going to try to fabricate an aluminum shield behind the carb to see if that will help a little.

Overall the car is quite usable now but I sure wish the government would get out of the gasoline business!!

[[email protected]]

Originally Posted by 29 Tudor

Here's the latest.....

Rebuilt carb and timing set correctly and the car runs fine... until the crummy gas we get now starts to boil in the carburetor. When cool, the car runs great. If I have to sit in traffic for a while, it runs poorly until the carb gets filled with cool(er) fuel. I stopped at the grocery store with the wife and shut her down and opened the hood. I could actually feel the fuel boiling in the carb. (It was 86 degrees outside, here in Central Florida) The Motometer was below the bottom and the fuel line and carb were cool enough to hold my hand on but there was no doubt the fuel was boiling!

I suspect I will just have to live with this although I am going to try to fabricate an aluminum shield behind the carb to see if that will help a little.

Overall the car is quite usable now but I sure wish the government would get out of the gasoline business!!

If you tried everything else by now, it sounds like it couldn't hurt to try a shotglass or two per gas fill up of Marvel Mystery Oil mixed in with the gas. It may help with the gas boiling of the gasahol in the carb.

If it does not help with this then just use the same shot glass yourself just with g good tasty alcohol. One or two shots per fill up should keep the Cops busy.

[29 Tudor]

Now there's a man after my own heart!

I won't use the alcohol in myself if I'm using the car but after that, a little alcohol is not a bad way to finish off the day.

Thanks for the MMO suggestion. I'll try that and see if it helps. Sure wish we could get real gas here!

Streve

[29 Tudor]

Well, in the interest of a complete thread, here's a bit of an update. One of our members was good enough to send me a spare 1/4 inch phenolic spacer for the carb to isolate the carb from the hot manifold. I added that along with two new gaskets. By the way, some were concerned that the GAV wouldn't line up when using the spacer but it lines up and works just fine. After the spacer, the problem was MUCH better. I replaced a head gasket and drove the car for a few days with no hood and there was NO problem. There was again a hint of a problem after putting the hood back on. That seemed to confirm the issue as heat in the carb.

Then, quite by accident, I discovered something that seems to have made a HUGE difference, to the point that the problem seems to be entirely gone... at least for now.

Here in South Texas, we are not allowed to have "real" gasoline. I think "they" believe we'll hurt ourselves if we have the real stuff. I have been running Shell premium (with the recommended 4 oz of MMO per 10 gal) because I read or was told that Shell premium had the lowest alcohol content that we could get. Over Memorial Day weekend, my wife and I drove the "A" about 50 miles to a state park for a picnic. (LOTS of waves and thumbs up by the way) On the way up and back, if I had to sit in traffic for a few minutes, when pulling away, there was a "hint" of the old starving problem.

Coming home, we were pretty low on fuel so I pulled into an Exxon station and filled with 87 octane regular, just to see how it would run. When we pulled out of the station, it ALMOST stalled as we pulled away. It hardly wanted to run and then .... almost like magic, it smoothed out and accelerated perfectly normally. Since then, I have driven it quite a bit in HOT weather (94 yesterday) to see if the problem is there. Not a hint of the starving!

I HAVE to believe the gasoline made the difference. Maybe the difference is 87 instead of 93 octane. Maybe the difference is the brand or MAYBE, I got lucky and got some with little to no alcohol but at this point, it's running GREAT, even in good old hot South Texas.

I am going to continue with various brands of 87 octane with the MMO and see what happens.

Has anyone else seen that kind of a difference in brands/octane?

Steve

[Rex_A_Lott]

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With a low compression motor like the A you're wasting your money buying anything but the 87. Thanks for the info.

[Mikeinnj]

Are you running a fuel tank filter (Inside the tank) see attached. My car did whay yours is doing until I put a tank screen in and it filtered debris in the tank from clogging the line outlet. Ran fine after installation.

[29 Tudor]

Rex A Lot: I realize I don't need 93 in the "A". I was using that to TRY to get fuel with little to no alcohol.

Mikeinnj: No, no filter but the tank is spotless and I DO have the original cast iron sediment bowl as well as the screen in the inlet of the Zenith. Both are, and stay, clean. As I outlined in my data above, I have plenty of flow when the engine/fuel is cool. The problem occurred when the engine/carburetor was hot. I could actually HEAR the fuel boiling in the carb after I shut the engine off and opened the hood.