Some more carburetor questions

JohnV2000

Member
I noticed that after clearing my fuel line, my tractor seemed to sputter a little bit while idling.

I read though my Super C manual, and it described how to set the idle screw. I turned the idle screw all the way in, then backed it out one full turn, per the instructions. I screwed in the throttle stop screw a little bit so it would not stall at slow idle speed.

I closed the throttle all the way and backed out the throttle stop screw to slow down the slow idle speed to a reasonable level. I also tried adjusting the idle adjustment screw, but no matter how I adjusted it, it would not idle smoothly.

The manual says that a small adjustment of the idle screw should let it run smoothly, but I could not get it. I eventually set the idle screw about one half turn shy of all the way in, and I had to choke the tractor a little bit to get it to run smoothly. Once choking it, it idled smoothly and ran better, but without the choke, it will not run smoothly.

I assume this is another opportunity for me to learn about tractors, and carburetors specifically.

Thanks,

John
 
sounds like idle circut in the carb isnt up to par. Have you ran a compression chech if you have weak cyclinders
it will never idle smooth.
 

It also ran a little rough under load, but when choked a little bit it was fine. It was running perfectly before I cleaned the fuel line.
 
For carb issues I always start
with the either test. Run it
at the trouble rpm's and spray
either around the carb and
manifold and listen for
changes. That will tell you if
there is a gasket leak. Of you
find nothing do a compression
test. Either of those will
tell you of your vacuum is low
which can cause carb issues.
If both of those check out ok
it's likely the carb. If you
start at the carb you might
not find the problem
 
Thanks for the info. I am really hoping it is simply a carb or fuel issue, because it was running very strong until the fuel line got clogged and I was forced to mess around with the carburetor and fuel line system.
 
If choking it makes it run better, it's too lean, probably some dirt restricting the fuel flow in the carb. Before I would
tear the carburetor apart I would take the mixture screws out and spray some carb cleaner into the holes, worth a try.
 

Ok, I will work through the system and try to figure out if there is any obstruction of the gas.

I cleaned the sediment bowl yesterday and I removed an obstruction from the inlet port into the sediment bowl. Am I looking for a similar obstruction causing it to run lean, or do I look for some dirt inside the actual carburetor?
 
Sounds like the idle jet is partially clogged.

Something you can try, remove the idle mix adjustment screw, spray some carb cleaner in the hole.

Replace the screw, see if it will adjust. Be sure the engine is idling down around 400-500 RPM, otherwise it won't be running on the idle circuit.

The mixture adjusting screw is actually adjusting air bleed, not fuel flow, so turning it in richens the mix, out leans it.

If that doesn't do it, the carb will need to come off and be cleaned out. Usually they can be eased apart without having to buy a kit. Try that first. Spray out all the passages, poke a small wire through the idle jet, be sure everything is clear. The gasket is important, it must seal around the small hole beside the venturi. That is where the idle fuel is drawn up.

It's a simple carb, don't be afraid of it. Just work over a clear surface so nothing gets lost.

Have fun!
 

Steve,

Thank you very much for your help. I will try what you suggested, but without a tachometer, how will I know if it is idling on the idle circuit or not? I have the throttle adjustment screw set pretty far screwed out, and it seems to be running very low rpm and quiet on idle.
 

I think I might be confusing some definitions.

When I say idle, I mean slow idle, like 500rpm. The manual also says fast idle. Not sure how that differs exactly.

When I have the tractor out of gear, I open the throttle completely, wide open throttle, and it still runs a little rough. When in gear, it similarly runs rough. The choke fixes it, and it runs smooth both out of gear full throttle and in gear with a load.
 
My Farmall c has only one fuel mix
adjustment. Not to be confused with the
throttle plate adjustment.

The fuel mixture adjustment is backwards
from many carbs. If you turn the fuel mix
fully clockwise, it will produce a rich
mixture turning the plugs black.

I have my screw to max CCW.

Use color of plugs to determine fuel mix.
 
If it was running fine before the fuel line
plugged off and now he has moved all the
adjustment screws it's more than likely in
the carb .you guys are going to get him all
confused talking about compression test and
all that. Just my 2 cents
 
I think I understand what I need to adjust, but I have one more question.

When the engine is running above idle speed, it is no longer being controlled by the idle adjustment screw, correct? Once above idle and under load, there is a main jet. Can I adjust that?
 
Add some seafoam to your gas,less gas in tank
faster seafoam works.
I get 1 of my little cases running rough i add a
can of seafoam to 2 or 3 gallons gas,run it till
its at operating temperature,shut it off let it
set for 24 hours then try it again.sounds like
some crud slipped into your carb.did you drain
the carb bowl and sediment bowl?
 
Yes, the main can be adjusted.

It's a little different. It adjusts fuel flow, so turning it out richens the mixture, in leans it.

Here's how to do it...

With the engine up to operating temperature, choke fully open, turn the screw in about 1/2 turn.

Open the throttle fully and quickly, listen to the engine response.

If it falters, hesitates, back the screw out 1/4 turn.

If it didn't hesitate, turn it in another 1/4 turn. Keep repeating and leaning it until it falters on quick acceleration.

Once that happens, start backing the screw out 1/4 turn at a time, repeating the test with each adjustment.

The goal is to have solid throttle response without hesitation. A single puff of black smoke is what you want to see.

Of course the carb alone won't fix other problems. If there are ignition problems, valve or compression problems, it won't run right until everything works together.
 
(quoted from post at 20:30:09 06/05/19) Yes, the main can be adjusted.

It's a little different. It adjusts fuel flow, so turning it out richens the mixture, in leans it.

Here's how to do it...

With the engine up to operating temperature, choke fully open, turn the screw in about 1/2 turn.

Open the throttle fully and quickly, listen to the engine response.

If it falters, hesitates, back the screw out 1/4 turn.

If it didn't hesitate, turn it in another 1/4 turn. Keep repeating and leaning it until it falters on quick acceleration.

Once that happens, start backing the screw out 1/4 turn at a time, repeating the test with each adjustment.

The goal is to have solid throttle response without hesitation. A single puff of black smoke is what you want to see.

Of course the carb alone won't fix other problems. If there are ignition problems, valve or compression problems, it won't run right until everything works together.

Thanks steve. I have a Zenith carburetor on my Super C, gas engine, and I cannot find the main adjustment, only idle. The diagram in my manual does not shown a main adjustment.
 
Sounds like the idle circuit is blocked. You'll probably need to disassemble the carb to fix it. You should be able to clear out any blocked passages with a fine, stiff wire. (I use monel fishing leader, but most folks don't have any lying around.)
 
Some don't have an adjustable main.

There is a plug in a horizontal galley on the bottom.

Take the plug out, take the jet out, or clean it in place.

Use the spray cleaner to rinse it out, poke it out with a fine wire.

Don't blow in the hole with compressed air. It can collapse the float!
 
To opening the passages in your carb the best thing is cutting torch tip cleaning tool. Carb cleaner will not always open plugging jets.
cvphoto25440.jpg
 

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