Miss at idle - any ideas ?

SteveB(OH) · Jul 8, 2018

Hi all,

I've owned my 48 8N for almost 20 years now. From the first day I took ownership I noticed a miss at idle and figured it was just a minor tune up issue. Over the years I've tried to hunt it down, and then just accepted it. Now I'm back to trying to get rid of the problem.

Here is some info:

[list:95d71b267e]1948 8N frontmount
Converted to 12v with EI last year with new "everything" (wires, plugs, coil, etc)
Had the carb rebuilt about 5 years ago by a member of this board
No trouble running, starts quickly, has plenty of power, accelerates with authority and without stumbling
It does not miss when first started, it only starts to miss after it gets hot.
There is no difference in the miss from when it as 6V points to 12V EI
It doesn't miss under load. If I have it at slow idle, and then drive up a slight incline the miss goes away[/list:u:95d71b267e]

Truth be known, everything else about the tractor is fine and it does everything I want without problem. But, I want to fix this if possible.

Here is a short video in case that helps:

https://dl.dropboxusercontent.com/s/4a60zn4zs7bvdxf/2018-07-07 12.35.42.mp4

Thanks for any ideas !

Roger in Iowa · Jul 8, 2018

I don't worry about it as mine does it too. At low idle compression gasses are extremely low volume. Once
throttle/governor opens carb mine goes away also. If not, then I would worry about it.

Roger in Iowa · Jul 8, 2018

If you really cannot stand it, up the idle speed just a bit. Burns more gas at higher low idle...

SteveB(OH) · Jul 8, 2018

(quoted from post at 10:14:33 07/08/18) If you really cannot stand it, up the idle speed just a bit. Burns more gas at higher low idle...

Ha ha, I have to keep the idle speed up just to maintain oil pressure ????????????

SteveB(OH) · Jul 8, 2018

(quoted from post at 10:14:33 07/08/18) If you really cannot stand it, up the idle speed just a bit. Burns more gas at higher low idle...

Ha ha, I have to keep the idle speed up just to maintain oil pressure

Royse · Jul 8, 2018

"Had the carb rebuilt about 5 years ago by a member of this board"

I would guess that was Gary (GB in MT), if so, there's likely nothing
wrong with your carb at all but each engine does breathe a little bit
differently so you might try adjusting your idle air mixture screw.
1/8 of a turn can make a big difference. In is rich, out is leaner.

If you decide to try that, keep track of where it was before you
started so you can put it back where it was as you might find it
then runs great when warm but not as well as it did when cold.

6 SLY PLACE · Jul 8, 2018

If all else fails the idle jet needs to be removed an open up the hole a hair with a pin vise

Dollar Bill · Jul 9, 2018

Miss at idle - any ideas ?

Retarded ignition timing will cause this problem.

SteveB(OH) · Jul 9, 2018

(quoted from post at 12:55:11 07/08/18) "Had the carb rebuilt about 5 years ago by a member of this board"

I would guess that was Gary (GB in MT), if so, there's likely nothing
wrong with your carb at all but each engine does breathe a little bit
differently so you might try adjusting your idle air mixture screw.
1/8 of a turn can make a big difference. In is rich, out is leaner.

If you decide to try that, keep track of where it was before you
started so you can put it back where it was as you might find it
then runs great when warm but not as well as it did when cold.

Thanks, I'll give that a try in the next day or 2 and report back

Hobo,NC · Jul 9, 2018

Sounds like its on the lean side :Lean misfire: Pop Corn Pop'N

In is rich, out is leaner.

Turn in till it labors at steady hard putt putt putt... Turn out till the putt putt put starts to break up like yours sounds I call it pop corn pop'N when its a uneven putt/pop,,,somewhere in between you will find your sweet spot..

If you can not drive it rich by truing it in then I would suspect a carb problem are false air getting in the the intake system...

If you can drive it rich that's s good thing it means your idle circuit is not restricted...

A rich mixture is hard to fire off that's why you get a laboring steady Putt Putt Putt when you add fuel at idle. Your nose and eyes will let you know its too rich also...

A lean mixture has a mix of firing events Putt Putt Pop Putt Pop Putt Pop Pop no pattern to it...

Forget about your oil pressure adjust at a low idle once set up then jack the idle back up to your satisfaction... I prefer around 7/800 RPM myself...

docmirror · Jul 9, 2018

Why not do some diagnosis? Rather than throwing parts, and guessing at settings, figure out what is different.

Read the plugs.
Leakdown compression test with 80PSI. Listen at oil breather, carb intake, and exhaust for leaks.
Standard compression test, how are the numbers in comparison?
Smoke check around intake manifold. Can also be done with carb cleaner when warm.
Test the resistance of the ign wires from spark plug tip to rotor wiper, look for one high or low.

Tim PloughNman Daley RIP · Jul 10, 2018

I see a rebuild in your future. A sticky valve will give you some snap, crackle, and pops too. You say, "...I have to keep the idle speed up just to maintain oil pressure..." -if your oil pressure starts dropping after the engine begins warming up, it is probably time for a rebuild. At start up oil pressure gauge should read about 27 PSI. As engine gets hot, it will drop slightly AT IDLE. If you have to throttle UP and/or put under load, to maintain a higher oil pressure reading, engine is worn out. At IDLE, when HOT, if oil pressure gets under 20 PSI or even worse, under 10 PSI, engine is in bad shape. The low oil pressure is not the cause of the popping as mentioned. Are you burning oil -do you have to keep pouring oil into it? Compression check?

Tim Daley(MI)

SteveB(OH) · Jul 10, 2018

I'm going with those who suggest that I'm running lean.

Yesterday I pulled the choke out ever so slightly while at idle and the miss went away. I didn't have time to dig into any carb adjustments, but I'll try that later this week.

fusion · Jul 10, 2018

What type fuel are you using ?

My Ferguson TO-30 always had a popping sound at idle
I started using non ethanol high octane gas and what a difference
starts better and seems like it has more power.

Hobo,NC · Jul 10, 2018

(quoted from post at 22:38:45 07/10/18) I'm going with those who suggest that I'm running lean.

Yesterday I pulled the choke out ever so slightly while at idle and the miss went away. I didn't have time to dig into any carb adjustments, but I'll try that later this week.

Apply the choke who'da thunk it :shock:

4play · Jul 11, 2018

Mine started running like that several years ago, I richened up the mixture screw and it got better, not great. I continued looking and found the intake gasket blown out, 2 of the manifold nuts were loose. It could be a number of things but finding a vacuum leak is quick and easy.

Nebraska Zach · Oct 22, 2023

Did you ever get this figured out? Mine is doing the same thing.

(quoted from post at 08:31:22 07/08/18) Hi all,

I've owned my 48 8N for almost 20 years now. From the first day I took ownership I noticed a miss at idle and figured it was just a minor tune up issue. Over the years I've tried to hunt it down, and then just accepted it. Now I'm back to trying to get rid of the problem.

Here is some info:

[list:591f38fef4]1948 8N frontmount
Converted to 12v with EI last year with new "everything" (wires, plugs, coil, etc)
Had the carb rebuilt about 5 years ago by a member of this board
No trouble running, starts quickly, has plenty of power, accelerates with authority and without stumbling
It does not miss when first started, it only starts to miss after it gets hot.
There is no difference in the miss from when it as 6V points to 12V EI
It doesn't miss under load. If I have it at slow idle, and then drive up a slight incline the miss goes away[/list:u:591f38fef4]

Truth be known, everything else about the tractor is fine and it does everything I want without problem. But, I want to fix this if possible.

Here is a short video in case that helps:

https://dl.dropboxusercontent.com/s/4a60zn4zs7bvdxf/2018-07-07 12.35.42.mp4

Thanks for any ideas !

SteveB(OH) · Oct 29, 2023

(quoted from post at 19:59:44 10/22/23) Did you ever get this figured out? Mine is doing the same thing.

Hi Zach,

Wow this is an old post from 2018 !!

Sorry to say that I never found the cause of the problem, and my 8N still misses a little bit at idle once it's warmed up.

But...

My tractor starts instantly hot or cold and does everything I need it to. So, I just don't worry about it any more.

Steve

Nebraska Zach · Oct 30, 2023

Thanks for the reply! I did some digging and saw that the most plausible reason could be the coil. I have a spare laying around and am going to try it when I get a chance.

Eman85 · Oct 30, 2023

(quoted from post at 18:30:17 07/09/18) Why not do some diagnosis? Rather than throwing parts, and guessing at settings, figure out what is different.

Read the plugs.
Leakdown compression test with 80PSI. Listen at oil breather, carb intake, and exhaust for leaks.
Standard compression test, how are the numbers in comparison?
Smoke check around intake manifold. Can also be done with carb cleaner when warm.
Test the resistance of the ign wires from spark plug tip to rotor wiper, look for one high or low.

Does anyone diagnose?

Miss at idle - any ideas ?

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