Intermittent misfire on 12 v converted Jubillee - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
 
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post #1 of 9 Old 05-23-2019, 08:37 AM Thread Starter
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Intermittent misfire on 12 v converted Jubillee

The subject is the 54 Jubilee from the thread below.

https://www.mytractorforum.com/38-fo...-turn-all.html

The previous owner converted it to 12v and added an electronic ignition system. It still starts and runs like a champ and I've been bushhogging with it maybe an hour a day on and off since I posted in the thread above.

Yesterday, it did something odd that I don't quite understand. I was at the far end of the 10 acre field bushogging some light weeds with the hog raised up and it started feeling like it was down slightly on power. I had my hood up to keep debris off the bushhog from going down my neck so once I took my hood down, I could hear that it was misfiring a little. I turned off the bushhog and headed back to the barn, which was around 8 acres away (lot is an acre wide and 10 deep). I got maybe halfway back to the barn and it started firing normally again and did so all of the way back to the barn until I parked it. The monsoons have started again so I won't have it out for a day or two now to see what it does.

All gauges work and were normal and did not move throughout, there was no sign of any smoke of any color at any time.

I saw a small stick had lodged itself between the distributor and the block by the coil wire so I pulled that out, coil wire may have been slightly loose but that didn't seem loose enough to be the problem.

It seems more possible that this was due to the fact that this was by far the longest I've used it since I bought it. I generally cut for an hour in the morning or evening when it's cool, and that's it for the day. Yesterday, I cut once in the morning and once around noon because rain was on the way and as mentioned, this is the far end of the field so I had to get back and forth both times.

Since there was no smoke or issues with the gauges that signaled a mechanical problem, I was thinking electrical. Working on other types of machines over the years, I've learned that electrical stuff tends to fail as it gets hot once it has some age to it. Since everything else in the ignition system should be new, that leaves the coil.

Referring to the thread above where it would not start, I have a resistor behind the dash so I probably have the original 6v coil? I assume there is a test for the coil windings but shouldn't I really just install a 12v coil and eliminate the resistor to make the entire system 12v?

Thanks

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post #2 of 9 Old 05-23-2019, 04:33 PM Thread Starter
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Re: Intermittent misfire on 12 v converted Jubillee

Should have searched before I posted, sorry about that.

I'll post what I found in case someone else sees this and doesn't search.

https://www.mytractorforum.com/38-fo...uestion-2.html

Courtesy of Mr. Nouveau Redneck:

Quote:
A coil that requires no external resistor in a 12 volt system should measure around 3 ohms across the primary. A coil that requires an external resistor in a 12 volt system is actually designed for no external resistor in a 6 volt system and should measure around 1.5 ohms.

You also asked whether it needed an external resistor, and if it still has the original coil then yes it needs an external resistor. if it has a true 12 volt coil then no, it does not require an external resistor.

There are coils that are labelled "12 volts, external resistor required" and lots of folks argue that these are true 12 volt coils, but they are not. They are designed to be run in a 6 volt system with no external resistor or in a 12 volt system with an external resistor, and the label is a warning that you need the resistor in a 12 volt system.

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post #3 of 9 Old 05-31-2019, 07:19 AM
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Re: Intermittent misfire on 12 v converted Jubillee

Another issue it could have been is water in the gas, which will cause the rough running until it is burned up. Probably remote cause, but had it happen one time to a smaller engine.
I'm not at all good with electrical systems, but converted mine back from EI to points, and cannot be happier. Starts immediately, and runs like a champ. I still need to check timing and carb tuning. Some folks who work on them told me they make it standard practice to remove the EI and go back to points when tuning them for customers.
Sounds like a runway you are clearing. Best regards.
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post #4 of 9 Old 08-08-2019, 05:38 AM Thread Starter
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Re: Intermittent misfire on 12 v converted Jubillee

And it started doing it again after running fine since I posted back in May. I'm selling the old girl and the bush hog because someone is going to start farming the back 40. Someone came to buy it and it started right up and idled fine for about 5 minutes while we talked and when I cut with it for maybe 5 minutes on light weeds, it started misfiring. Again, no smoke, gauges are normal.

I apologized to the guy and saw him off and went back to the tractor. It fired right up but still had the misfire. I did notice that if I throttled down below halfway the misfire cleaned up. Throttle back up and it came back.

It's been in the 90's here for weeks and I thought it was heat related last time so I'm still thinking weak coil unless someone else has a different thought.

Thanks, I really need to room in my barn and the money right now so I'd like to get this sorted and sold.

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post #5 of 9 Old 08-08-2019, 07:04 PM
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Re: Intermittent misfire on 12 v converted Jubillee

If you think it is the coil next time it acts up pull a plug wire to see if it is bright blue or yellow.




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post #6 of 9 Old 08-19-2019, 05:54 AM Thread Starter
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Re: Intermittent misfire on 12 v converted Jubillee

I have people lined up to buy this as soon as it is solved but not getting anywhere. Still starting immediately on turn of the key, idles decently at low throttle, misfires to a stop above mid throttle. No smoke, not backfiring, gauges are normal, just misfiring at higher rpm's.

I've tried 3 different coils and the only one that works well is the original, It's got an odd number NAPA doesn't seem to be able to cross. With that coil, it starts right up and runs pretty well until you go to high throttle level and at that point it will misfire. This is with the engine cold so it's not a heat related coil breakdown as I thought. Coil tower does have a chip that slightly affects wire tightness but not enough to cause this.

Plugs and wires were replaced right before I bought it and it ran well all summer. I pulled all of the plugs to make sure they were tight and checked the electrodes. They were all light grey and consistent, no signs of gas or oil fouling so I believe the electrical system is solid.. I have a compression tester but we recently moved and I have no idea where it is. It doesn't sound like it's down a cylinder, not a lope.

With the coils and wires/plugs seemingly okay I started thinking it was running out of gas somehow.

I installed a new screen and seal on the float bowl, TSC didn't have a complete assembly so I got the parts. Seal was falling apart and the screen was black with grit so they needed to be replaced but they didn't help much at all. Started right up, idled for a while, and eventually misfired to a stop.

The new inline filter was longer than the original but wasn't damaged on the end when I pulled it back out to check it so it must be okay . While it was off, I checked to be sure the metal fuel line from the bowl was clear and it seemed to flow just fine. I found that the rubber fuel line pulled off the carb with little resistance so I replaced the fuel line and clamps so that's much better than it was.

All that made it better but still not great. Would start right up, idle a little longer and better but still not the greatest.

I pulled the cap off of the distributor (this tractor has the electronic ignition conversion), made sure the cap contacts weren't corroded, Removed the rotor and it looked fine, key kept it stationary on the shaft. I tried to get the cover off of the distributor body to look below but there is a really small C clip or something on the distributor shaft holding it on that I was sure I would lose if I tried to take it off. I made sure the rotor key was back on the shaft, that the cover was aligned properly with the oiler, wiped down the contact on the top of the rotor, and put it back together.

It started right up, idled at various speeds as long as I wanted it to (till the thermostat opened), and only misfired badly at really high idle. It acts almost like it's going to clear itself up and start running like a champ now and again at lower idle speeds but it just can't quite do it. So monkeying with the distributor like I did seemed to help.

Could the whatever provides ignition advance (counterweights since there is no vacuum advance) cause something like this? On a car with a PCV system I would suspect a vacuum leak somewhere but I don't know where it would be on the tractor.

Any ideas would be welcome. I'd really like to find the old girl a new home to clear space in the barn and raise money for another project.

Thanks

1954 Ford Jubilee
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John Deere 185
John Deere LX188
John Deere 345
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post #7 of 9 Old 08-19-2019, 10:30 AM
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Re: Intermittent misfire on 12 v converted Jubillee

You can check to see what cylinder is the problem. When the tractor is running and misfiring, take off 1 spark plug wire at a time and see if there is a major change in the way it runs. If you pull off a wire and almost no change in the way she runs, the problem is in that cylinder. It will not find the exact problem but, you might get it narrowed down. You might get "zapped" so be carreful.
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post #8 of 9 Old 08-19-2019, 07:16 PM Thread Starter
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Re: Intermittent misfire on 12 v converted Jubillee

Quote:
Originally Posted by WI_Jeff View Post
You can check to see what cylinder is the problem. When the tractor is running and misfiring, take off 1 spark plug wire at a time and see if there is a major change in the way it runs. If you pull off a wire and almost no change in the way she runs, the problem is in that cylinder. It will not find the exact problem but, you might get it narrowed down. You might get "zapped" so be carreful.
Thanks for the response!

Wouldn't the condition of the plugs tell me which cylinder is the issue, if it was a cylinder misfiring? They are all light grey and appear exactly the same one to another. I have gotten zapped, which is why I avoid pulling plug wires, haha.

Also, I've had dead cylinders give me a more constant misfire at all speeds. This one can go away completely at lower idle speeds.

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John Deere 180
John Deere 185
John Deere LX188
John Deere 345
92 Dodge Cummins 12 valve dually
84 VW Vanagon getting a Subaru transplant
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post #9 of 9 Old 08-20-2019, 08:30 PM
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Re: Intermittent misfire on 12 v converted Jubillee

With all the work done on electrical, what have you checked for fuel and air? Maybe starved for one or the other at high rpm and load.
I saw replaced bowl screen, how about the screen at the carb? Could gas cap vent be plugged? What happens when it is missing and you give it some choke?

Just a few simple things that can cause similar symptoms.


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