Fine tuning Needed?? Watch Video

[RTR]

Farmall 140 with Adjustable Zenith CarbUretor. Professionally rebuilt (carb sitting in my safe for a year). Tractors starts east and runs great. Runs strong with no smoke but when it is moving along at able 1/3 to 1/2 throttle , it has a miss. Once you feed the onions to her, it doesn t hesitate and runs smooth and strong. I noticed if I pull the choke out about 3/4 it clears that up and doesn t change anything else. No passages should be blocked. Fuel system gone through on tractor. If choke is pulled all the way out it will kill the engine. I m thinking it needs an adjustment for more fuel but wanted to ask here first. The zenith carb that is on it is an older cast Iron one like on a Super A with the adjustable Main needle jet. Will attempt to attach a video.

 

[560Dennis]

Whats your vacuum test gage read ?

 

[Janicholson]

Screw out the main mixture 1/2 turn at a time. It could also have a bad spark plug that misses at a particular speed. Jim

 

[RTR]

(quoted from post at 04:06:52 08/13). Will attempt to attach a video.

Here is the video. Towards the end as the tractor heated up , the missing started. First part was after about 15 min run time. The last part of video when I noticed the missing was about 45 min of run time.

https://youtu.be/AVh0rw5uBzM

This post was edited by RTR on 08/12/2022 at 08:02 pm.

 

[Janicholson]

With the information that it happens as it gets warm, I suggest feeling the ignition coil as the misfire starts. if it is hot
(real hot) I would replace it. Jim

 

[RTR]

(quoted from post at 06:55:17 08/13/22) With the information that it happens as it gets warm, I suggest feeling the ignition coil as the misfire starts. if it is hot
(real hot) I would replace it. Jim

all distributor components and ignition coil are new but we all know that doesn t mean anything. Reason I lean towards a carb adjustment is because the choke seemed to help. I just don t understand what adjustment is needed (if any).

 

[RTR]

(quoted from post at 05:10:05 08/13/22) Whats your vacuum test gage read ?

I ve never checked one that way. Can you explain??

 

[560Dennis]

(quoted from post at 20:01:11 08/12/22)

(quoted from post at 05:10:05 08/13/22) Whats your vacuum test gage read ?

I ve never checked one that way. Can you explain??

https://dannysengineportal.com/vacuum-gauge-test-tells-you-a-lot-about-the-condition-of-your-engine/
Here an example in link that does inspection and analysis way better than I can explain . Your manifold has a 1/8 pipe plug port the factory put in there for you to use to analyze problems , connect your gage to it and compare gage reading actual to examples.
Tell you exactly what s going on in that engine vacuum system ( big air pump)

If you have a newer manifold , I had to drill and tap a pipe port for 1/8 npt on my new manifold for the super C . It s not hard just location of port ,tap drill correct, tap wrench tap to correct depth.,get 1/8 barbed hose fitting and attach the vacuum gage to port ,start engine ,observe gage ,do your tuning using gage ,or correct the issues per readings .

 

[RTR]

(quoted from post at 18:13:57 08/13/22)

(quoted from post at 20:01:11 08/12/22)

(quoted from post at 05:10:05 08/13/22) Whats your vacuum test gage read ?

I ve never checked one that way. Can you explain??

https://dannysengineportal.com/vacuum-gauge-test-tells-you-a-lot-about-the-condition-of-your-engine/
Here an example in link that does inspection and analysis way better than I can explain . Your manifold has a 1/8 pipe plug port the factory put in there for you to use to analyze problems , connect your gage to it and compare gage reading actual to examples.
Tell you exactly what s going on in that engine vacuum system ( big air pump)

If you have a newer manifold , I had to drill and tap a pipe port for 1/8 npt on my new manifold for the super C . It s not hard just location of port ,tap drill correct, tap wrench tap to correct depth.,get 1/8 barbed hose fitting and attach the vacuum gage to port ,start engine ,observe gage ,do your tuning using gage ,or correct the issues per readings .

I think I see what you mean. But by looking at the gage to tune it, what am i looking at and shooting for??

 

[RTR]

(quoted from post at 06:25:05 08/13/22)

(quoted from post at 04:06:52 08/13). Will attempt to attach a video.

Here is the video. Towards the end as the tractor heated up , the missing started. First part was after about 15 min run time. The last part of video when I noticed the missing was about 45 min of run time.

https://youtu.be/AVh0rw5uBzM

This post was edited by RTR on 08/12/2022 at 08:02 pm.

Didn t know if I should idle air screw or the load needle with the issue I m having. ??

 

[560Dennis]

Highest possible with steady needle normal is 17 to 22 . Hp performance engine are low 17 or less with big cam shaft . You should be about
18 to 21 steadying neddle at idle . Meaning the needle wilt move about one line or less being a four cylinder.

The charts are important ,for diagnosis.

Idle screw if I remember on zenith is 3/4 to one turn open ,. Mixture screw Ive never had one , rotate it till it stumble and gage goes
inconsistent. Rotate open till gage inconsistent gage rotate half distance to be smooth and steady needle , run it high idle watch gage ,tourn
idle to help needle smooth out , turn mixture screw to smother if necessary .

Try it and run it hard ,replete test if necessary.

Now if gage is inconsistent like in charts nothing will improve that engine till those issues are corrected.
A lot of how to videos on your tube on vacuum tuning , very helpful in explaining issues .