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diagnosis advice?

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adsmith

02-11-2020 10:25:51

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This is a 1949 front-distributor 8N model. It is not a show tractor -- it is a durable and trusted tool.

Original options:
- Sherman Hi/Lo transmission
- Allied hydraulic trip-bucket loader driven by front-shaft pump

Recent maintenance:
- 2016. Converted professionally to 12V and electronic ignition. I think they used the kit available at YT with the cylinder-shaped coil
- 2017. Replaced main hydraulic cylinder, washers, overpressure valve, and some seals.
- 2019 summer. Replaced external hydraulic lines and added two-gang hydraulic controller. one for original bucket, the second for a hydraulic 3-point toplink

Late this fall, it started running rough under load, and would not get up to RPM even with open throttle. So, I started going though everything methodically.
0. Replaced sparkplugs with NEW (Autolite 437s) and changed engine oil with generic 10W30.
1. Complete carb rebuild (original body, new seals and pins and all)
2. Drained fuel tank twice and blew out fuel line. Cleaned and replaced filter in sediment bowl.
3. Replaced starter solenoid with NEW. (It shorted out after 70 years when I was testing the new carb)
4. Replaced governor with NEW. (the original one was probably fine actually)
5. Replaced manifold and gaskets with NEW. I sometimes saw exhaust around the manifold in cold weather, so was wondering about a vacuum leak. (but the spray test never made any change)
6. Replaced crappy straight-tube muffler with a new compact car muffler.
Now I can hear the engine noises better.
7. Added a digital proofometer that picks up from plug#4 so I can watch engine RPMs more accurately.

Wow, it starts great and can run from 500rpm to almost 3000rpm amazingly well. Great power delivery. (I don't run it over 2400rpm except if I need a quick kick to get out of a hole. Muffler starts to glow pretty quick lick a hotrod up there.)

OK, sounds fantastic!

but then.... I get bogged down in a deep icy snow drift, and it goes back to this rough-running low-power behavior. Idles a little rough, and wont go over 800 or 1000rpm according to the plug #4 tach. Almost no throttle response.
Driving along a clear road, it seems to run fine. Hit a big bump or put the engine under heavy load, and it seems to get caught like this.

Sometimes I can kill it and restart, or I can try to rev up-and-down a little, and it will come back to running normally.

Some interesting tidbits:

When it's running funny, I can short each of the spark plug wires with a wrench, and I get spark to the engine block.

BUT! When I short plug #4, the engine dies immediately. I wonder if it's just not firing on a couple cylinders, then comes back somehow. But, I have at least some voltage to each plug stem.

Do these ideas seem sane? Any other ideas?

1. Maybe moisture or gunk in the distributor, enough to reduce spark voltage?

2. Maybe a weak or loose connection on the ignition coil?

3. Maybe stuck valves?

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ASEguy

02-13-2020 04:29:51

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

I don't think it's stuck valves. It almost sounds like a degrading of the voltage to the ignition system. I would verify 12v supply voltage to the electronic ignition with a load device. At minimum an old test light, not a volt meter. When it dies hop off and check the brightness. If dim, check the voltage. If low, back up to the next connection and test there. It is very important that you check it immediately, not after you go find a test light. You should put the load light and the voltmeter in the toolbox. Pay attention for loose or corroded terminals. Wires can also go bad internally, so with the leads hooked up wiggle test wiring as you go. Hope this helps. Gerard

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Jim WI

02-12-2020 18:15:00

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

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I'd go just about the opposite. When he grounds #4 the engine dies. When he grounds one of the other three it doesn't. This makes it seem like #4 is the only one that is working well.

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Rogeriniowa

02-12-2020 17:21:06

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

Muffler should not glow. Maybe manifold but has to be a lonnng harddd pull. You got other problems, timing or lean carb, or???

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Lynn Patrick

02-12-2020 06:16:29

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

Just because parts are new does not mean they are working correctly. My 3000 acted the same way, would run intermittently on 3, then 2. then 3 cylinders. And when 1 cylinder of a 3 cylinder is not firing it is VERY noticeable! My problem was 1 of the new Autolites was misfiring.

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Den N Ms

02-12-2020 02:53:38

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

Adsmith,you write, I get bogged down in a deep icy snow drift, and it goes back to this rough-running low-power behavior. Idles a little rough, and wont go over 800 or 1000 rpm according to the plug #4 tach. Almost no throttle response.

You got the inside of the distributor cap wet from melting ice and snow kicked back on it from the fan.You need to replace the old bad gaskets with new ones.

Dry the cap,distributor and coil out with a hair dryer put cap ,coil back on making sure everything is in place.Wires ,proper firing order #1,#2,#4,#3 and tight.

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8NChris

02-11-2020 23:14:56

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

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Sediment in the fuel tank can cause similar symptoms. After the engine sits the trash settles back down and it runs good till kicked back up. If all is good there I would check primary and secondary coil resistance. Coil specs can vary depending on what wires and plugs they were designed for. Sometimes the intermittent faults are hard catch. Test the coil when it is at ambient and normal operating temperature. The wires and plugs have a resistance spec also but if the symptoms are unchanged between repairs I would look at the coil and its power source first. Vibration, moisture and heat can play havoc with electrical connections. Load testing ground/power sources with a 12 volt headlight usually shows the weak link.

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Caryc

02-11-2020 17:30:45

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

You sound like you don't like my reply. You have posted a very wordy account of your tractor. But, nowhere in all those words did you say you checked the fuel flow by removing the carb bowl drain.
One could just loosen the fuel line from the brass elbow and see a good fuel flow, But seeing a good fuel flow from the carb bowl tells you a lot more. All you ever said is "there is a good fuel flow".
From where, you did not say.

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Hobo,NC

02-11-2020 16:37:07

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

Know good clean non-contaminated fuel is hard to beat...

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adsmith

02-11-2020 15:31:34

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

What? No, sorry, you are making assumptions about my state of mind and actions that are not correct.

In historical fact, I checked fuel flow right away. BUT I also knew that the filter hadn't been checked in about a decade, so it was a good maintenance item.

In the above post, I described what had been done to help give context to the situation.

In fact, every time this happens, I check the spark to each plug (grounding test) and fuel flow... and to my judgement they seem OK every time.

So, let me rephrase the question more succinctly:

"I have a problem that acts like misfiring cylinders, and it comes and goes. My tests show that I have some amount of spark to each cylinder, I have good overall fuel flow, and I probably don't have a vacuum leak. What else should I consider?"

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Caryc

02-11-2020 14:49:15

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

I'm sorry but you did steps 0. , 1. 2. before even knowing if you had a good fuel flow from the carb bowl. Fuel flow and spark are always what you check first.
Something you may not know, you said you checked the fuel line, did you remove the brass elbow on the carb that the fuel line goes into? It has a strainer on it. I have had a tractor start running very badly and that elbow strainer was the cause. That's why you see a picture of a nice new one.

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adsmith

02-11-2020 13:09:35

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

Thanks for the suggestions.

Yes, I have good fuel flow.

Today I will buy a spark tester that is better than a simple long screwdriver.

To clarify, I wasn't just throwing parts at it randomly. Each part was to eliminate a possible hypothesis as efficiently as I could see. I figured the post was already long enough without writing a diagnostic autobiography.

Standard hypotheses in order:
1. spark? has new plugs with correct gaps. Cranking with them out, i have visual spark. When running, I have see shorting from metal boot to any nearby ground, so the distributor isn't completely dead. 2. fuel? have good fuel flow to carb. jets are clear and float is free inside the carb. Fuel flow remains good when running well and when running poorly.
3. air? seem to have good tight seal on new corrosion-free manifold.

That's why I was wondering what other diagnostic tests to try. I see why the inline spark tester is better than doing a simple short, so you can compare them more accurately while normally.

I'm not sure how to test fuel delivery on a per-cylinder basis. Any advice there?

----- --

I can explain why I did those things in detail if you like...

The one thing that was unnecessary for diagnosis was the governor. My understanding is that "good idle, good fuel flow, but will not rev up under load" was typical of a governor whose marbles were grooved. So, I opened it for inspection. The marbles and everything were in OK shape, but I thought the return springs were getting weak, and anyway I needed new gaskets. The whole governor was practically the same price as the rebuild kit, so I just got that. In fact, once I had the new quiet muffler on after the rest of this, I could hear that the engine wasn't running as smoothly in this "will not rev up under load" scenario, so the governor probably wasn't necessary. (but I didn't know that until I had already done the manifold and exhaust)

The induction proofometer shouldn't be shorting anything. It is an insulated wire with no free end. Another test I could do is move the induction pickup from cylinder to cylinder, and see if they all read the same RPM. That is, are they getting roughly the same number of triggers from the distributor?

Anyway, it is a useful diagnostic tool to have around, since this 8N doesn't have the governor rpm/hour proofometer, so I can see "oh, it's running rough at 1200 but not 2000" and "oh, this is what 500rpm idle sounds like versus 800rpm"

But, I will certainly take the advice to remove it from the system when trying to diagnose varying spark.

Manifold- Because I originally suspected a fuel problem (like everyone above), and the carb and tank were already clean, and because I saw hot exhaust around the engine, I wanted to exclude a vacuum leak. So I took the opportunity to remove it the rusty original exhaust manifold and clean off the original gasket, and replace them. The manifold was a bit expensive, but I wasn't sure I could guarantee a good gasket seal with a rusty hunk of metal.

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Bruce (VA)

02-11-2020 10:48:04

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

You could have a spark issue.

You could have a fuel issue.

Don�t guess. Troubleshoot. See tip # 13.

You need to answer 2 questions before you do anything else:

With the bolt in the carb bowl removed and the gas on, will the fuel flow fill a pint jar in less than 2 minutes?

Next, get out your adjustable gap spark checker * , open the gap to 1/4", hook it up, turn the key on and crank the engine. Does the spark jump 1/4"? Post back with the answers.

And do not buy a new part for the tractor until you can answer this question: how do I know the part on the tractor is defective?

And remove that " tach" from # 4. Once you narrow the problem to spark or fuel, post back and tell us what you found (and how you found it) and you will get plenty of help to get your tractor running.

* Don't own an adjustable gap spark checker? Buy one! Not a test light! Until then, take an old plug, open the gap 1/4" ground it to the head & look for spark. It�s not the color of the spark that counts; it�s the distance it jumps.

Link

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Caryc

02-11-2020 10:42:43

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

You really don't say what you've done to test the thing besides throwing new parts at it. The first thing I would do is get a good spark tester and test the spark on each cylinder.
The next thing I would do is check the fuel flow by removing the plug in the bottom of the carb bowl. It should show a steady flow of fuel. This is the tester that I use. The spark should be able to jump a quarter inch gap.

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gajack

02-11-2020 10:42:22

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

Sir, May I suggest to disconnect the "proofmeter"
which you have installed on the #4 plug when checking for spark on that plug. Very possible you are grounding
the ignition causing it to die. Just a quick read from
your trouble shooting points.
Will be open for others with much more vast experience
to address your tractor.
good luck, gajac

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Jim L WA

02-11-2020 10:38:31

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Re: diagnosis advice? in reply to adsmith, 02-11-2020 10:25:51

My first thought is that it's not firing on all four at times. I'm not sure how you are checking for spark with wrench, but evidently there is some spark there. So, I would check inside the distributor and cap for moisture for sure, and while your at it check the distributor for worn bushings.

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oldsarge

02-11-2020 19:49:25

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Re: diagnosis advice? in reply to Jim L WA, 02-11-2020 10:38:31

Or maybe,possibly,perhaps,you might have 3 and 4 switched,sounds far fetched,but it kin happen

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btzj02

02-12-2020 01:37:25

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Re: diagnosis advice? in reply to oldsarge, 02-11-2020 19:49:25

You seem to indicate in your testing that the problem comes and goes making me believe an electrical problem. Also your comment about #4 cylinder immediately killing the engine when grounded would point me in that direction to start my search. Because the #4 cylinder is acting differently then the rest of the cylinders I am guessing that the problem lies between the distributer rotor and the #4 cylinder spark plug. To minimize the variables I would disconnect the proof meter connection and then systematically rule out, one at a time, the Rotor, Distributer cap, #4 spark plug wire and the #4 spark plug. This is an interesting problem. Please let us know when you find the solution!

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Snowplow

02-14-2020 10:04:26

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Re: diagnosis advice? in reply to btzj02, 02-12-2020 01:37:25

Just a thought but it sounds like your running very lean. Timing may be way off. That may make for a beautiful idle and a real smooth rpms. But not so great under load. Also may cause heat which is causing that manifold to glow. May not be the only problem.

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