Why does my choke have to on for tractor to run?

[LeFeu]

I have a 1955 VAI Case that I am having some carb problems with. I have cleaned and rebuilt the carb, fuel tank was chemical cleaned and lined. The only way I can keep the tractor running is to have the choke closed to the 3/4 position. It does however, run pretty smooth this way.
I have tried adjusting the carb but no matter what I do, the choke has to be partially closed in order to run.
After the carb rebuild, I had removed the inline fuel filter as suggested by a tractor mechanic friend of mine, so filter is not the problem. (He had suggested that the inline fuel filter might have been the source of my original problems before the rebuild. His position was that naturally aspirated carbs sometimes do not have enough vacuum to pull adequate fuel. I was a little sceptical at the time (still am) but tried it anyway)
Any advice would be much appreciated. (I also have other issues to address but one thing at a time).
Thanks

 

[MarkB_MI]

Idle circuit blocked. Poke a fine, stiff wire through all the carburetor passages.

 

[Goose]

Same thing happened on a VAC once. The butterfly shaft was worn so loose air was being drawn in around the shaft causing the mixture to be too lean.

 

[da.bees]

Idle circuit blocked. Poke a fine, stiff wire through all the carburetor passages.

Right after you squirt carburetor cleaner with straw into passage then follow wire up with compressed air .

 

[Janicholson]

I have a 1955 VAI Case that I am having some carb problems with. I have cleaned and rebuilt the carb, fuel tank was chemical cleaned and lined. The only way I can keep the tractor running is to have the choke closed to the 3/4 position. It does however, run pretty smooth this way.
I have tried adjusting the carb but no matter what I do, the choke has to be partially closed in order to run.
After the carb rebuild, I had removed the inline fuel filter as suggested by a tractor mechanic friend of mine, so filter is not the problem. (He had suggested that the inline fuel filter might have been the source of my original problems before the rebuild. His position was that naturally aspirated carbs sometimes do not have enough vacuum to pull adequate fuel. I was a little sceptical at the time (still am) but tried it anyway)
Any advice would be much appreciated. (I also have other issues to address but one thing at a time).
Thanks

Fuel is delivered by gravity, not vacuum. So the issue is internal to the carb in this case. If it keeps running with the choke at 3/4, the supply is probably OK. Passages in the carb are partially or completely plugged. Jim

 

[Jim.ME]

Just a simple look at the choke plate, while moving the control, to see that something hasn't gotten hooked up backwards and when you pull the choke it is actually opening. I have seen such before.

 

[TheBartman47]

Check for air leaks everywhere, even intake gaskets. Somewhere it's sucking in air besides the carb. (carb itself could also have air leaks somewhere). While running, spray a little bit of carb cleaner at various places and see if at any point it makes the RPMs go up a little. If so, then you've found the air intake leak.

 

[Ray,IN]

Fuel is delivered by gravity, not vacuum. So the issue is internal to the carb in this case. If it keeps running with the choke at 3/4, the supply is probably OK. Passages in the carb are partially or completely plugged. Jim

You might want to rethink this about vacuum in a carb. The vacuum comes from the cylinders intake stroke. The carb pulls gasoline through the needle valve/jet into the air stream.
It can be either the choke or throttle plate shaft or a dirty needle valve or passage-way, and/or loose carb mounting bolts. I would not run anything metal through one of these very small passages.

 

[Mcrafty1]

I have a 1955 VAI Case that I am having some carb problems with. I have cleaned and rebuilt the carb, fuel tank was chemical cleaned and lined. The only way I can keep the tractor running is to have the choke closed to the 3/4 position. It does however, run pretty smooth this way.
I have tried adjusting the carb but no matter what I do, the choke has to be partially closed in order to run.
After the carb rebuild, I had removed the inline fuel filter as suggested by a tractor mechanic friend of mine, so filter is not the problem. (He had suggested that the inline fuel filter might have been the source of my original problems before the rebuild. His position was that naturally aspirated carbs sometimes do not have enough vacuum to pull adequate fuel. I was a little sceptical at the time (still am) but tried it anyway)
Any advice would be much appreciated. (I also have other issues to address but one thing at a time).
Thanks

The first thing I would do is put a fuel filter back in the fuel line between the tank and carb...then follow the advice of those in the know...my vote would be a plugged idle circuit and/or a worn throttle shaft.

 

[560Dennis]

you can try
Suggest you can pack some clean cup grease around the entire throttle shaft of that carburetor , both ends of shaft. . That will briefly seal off leak Enough . Iif iissue goes away,issue of throttle shaft this will change to normal and stay normal for a short time.

You could also if the intake manifold has 1/8 pipe plug ,remove it and put a vacuum guage instead. Then you do a vacuum test on your tractor Engine . I’ve also drill and tapped 1/8 27 pipe thread Into the intake manifold and put in a vacuum port for testing intake system. Get a new 1/8 pipe plugto ,install when finish testing, that way you have for future .
just a thought how to measure improvement of issue To get it back to normal.

 

[showcrop]

Along with checking the idle circuit, understand that your idle mixture screw controls air not fuel so you turn it in to richen the mixture, and in turn reduce the need for choking.

 

[Janicholson]

The first thing I would do is put a fuel filter back in the fuel line between the tank and carb...then follow the advice of those in the know...my vote would be a plugged idle circuit and/or a worn throttle shaft.

With respect, the collective experience on this forum is that extra fuel filters often create more problems than they solve. there are fuel filters that are acceptable on gravity feed systems. NAPA carries them as well as others. they are larger and have a design that flows mor freely than the typical plastic in line filter. With fuel injection micro filtering is needed. Jim

 

[Jim.ME]

This type should be an acceptable type to use in a gravity flow system.

 

[Rich'sToys]

I've got metal ones on a few of my tractors. Never had a problem. A couple times one has plugged up, but that just tells me that it's doing its job. I just replace it and move on.

 

[Mcrafty1]

With respect, the collective experience on this forum is that extra fuel filters often create more problems than they solve. there are fuel filters that are acceptable on gravity feed systems. NAPA carries them as well as others. they are larger and have a design that flows mor freely than the typical plastic in line filter. With fuel injection micro filtering is needed. Jim

The OP said he removed the filter, I assumed the ONLY filter that was there...and it still wouldn't run, with the same all do respect I never realized a filter before the carb on anything, let alone an old tractor was a negative.

 

[LeFeu]

Idle circuit blocked. Poke a fine, stiff wire through all the carburetor passages.

MarkB
Thanks for your advice. Disassembled carb again, poked fine wire through all passages followed by carb cleaner. No change.

 

[LeFeu]

Same thing happened on a VAC once. The butterfly shaft was worn so loose air was being drawn in around the shaft causing the mixture to be too lean.

Goose,
Thanks for your reply. I checked play on the butterfly shaft and was surprised at how loose it felt. I found a small O-Ring, greased it up and slide it over the shaft between the housing and linkage. It took away the play around the shaft and I was optimistic about my fix as I reinstalled the carb. Unfortunately, no change. I'm pretty much out of ideas and will have to look at getting a new carb I guess.

 

[LeFeu]

Fuel is delivered by gravity, not vacuum. So the issue is internal to the carb in this case. If it keeps running with the choke at 3/4, the supply is probably OK. Passages in the carb are partially or completely plugged. Jim

Thanks Jim.
I was quite confident it wasn't a fuel supply to the carb problem. I took the carb apart again and blew through all passages. No change. It will run awhile with the choke pulled out then start to sputter and die. I can keep it going for awhile if I play with the choke but it eventually sputters out.

 

[LeFeu]

Just a simple look at the choke plate, while moving the control, to see that something hasn't gotten hooked up backwards and when you pull the choke it is actually opening. I have seen such before.

Thanks for the advice. Checked the hookup and it is ok. So that's not the problem in this case.

 

[scootergmc]

Don't give up.

Spray some brakeclean around the carb while running. If the engine surges, you have air entering somewhere. Problem found.

If you didn't replace your throttle/choke tube shaft felts/rubbers, do it. Double check your float height. Check your adjustment settings.