Runs for 5 minutes then quits

I have a 12V, 1950 8N front mount that I've used for plowing and disking almost 8 years in a 1/4 acre garden. It started and ran fine when I put it up and disconnected the battery last fall. I tried plowing two weeks ago and had to choke it more than normal to get it running at first, but then it started idling OK with no choke. (Note: normally I can stop choking immediately upon starting with no issues.) I plowed for 2-minutes, then the engine started surging, and I had to throttle up to keep it running. It got so bad, I couldn't keep plowing and took it back to my garage.

My first thought was a clogged gas line, so I removed the 7/16" nut at the bottom of the carb and saw gas draining just fine. I also used a flashlight to peek inside the tank at the in-tank filter, and it looked clear. Also saw plenty of gas over the top of post going to the glass bowl while looking in the tank. I took the glass bowl apart and the screen inside was clean, and there was no sediment in the bowl. I set a 5 gallon bucket under the carb and removed the 7/16" plug again and let gas run for 5 minutes. It was a solid, steady stream that would have easily filled a pint jar during that 5 minutes.

My next thought was maybe time to change points. But first, I checked to ensure I had battery voltage at the top of the coil, and I did with 12.5V. (Had to bump the starter a few times to get that. First three readings were 8.7V.)

After ordering parts and waiting a week, I replaced the points with blue streak points ($$$!!!) bought from this site and replaced the condenser and rotor. I also replaced the distributor cap because the old one had a crack at the #2 plug connection. I've changed points on this tractor before, and while I'm not a mechanic, the process went smoothly. I checked continuity with coil off and on with points open and closed per instructions I've seen elsewhere in this forum from "Bruce (VA)." Continuity checked out fine, and there was no evidence of continuity to the distributor body with the points open whether the coil was off or on. I reinstalled the distributor/coil as an entire unit. This allowed me to check continuity one last time from the top of the coil to the distributor body with everything put together. Had continuity when points were closed and none when points were open.

Thinking I'd probably solved the problem, I went back out to plow today. Upon starting, I had to choke more than normal but less than two weeks ago. Thinking that might just be a transient fluke caused by my recent work, I commenced to plowing and the same surging occurred after about 5 minutes. I immediately removed the 7/16" plug from the carb again and had plenty of gas flow.

Got the tractor back to my garage and started checking voltage again from the battery through each component. Don't really know why since I checked voltage to the coil again, and it was 12.5V, but I was scratching my head and checking anything I could think of! I bumped the starter and then read 8.7V at the coil. Based on what I've read in this forum, that seems appropriate.

Some additional info: I have a 2.5 ohm 12V coil and an RU-100 resistor that measures 1.2 ohms. Both were on the tractor when I bought it 8 years ago. I store my tractor under a tarp when it's not in use, and it stayed dry since putting it up last fall. I replaced the ignition key switch with a heavy duty toggle switch a few years ago, the last time I changed points. (Yes, I did check the toggle switch continuity separately during my troubleshooting today.)

I'm stuck! I need to plow ASAP. What should I try next?

Thanks!!!

the first thing i'd try is jumping around that resistor.

Remove the ceramic resistor. All you need is the OEM ballast resistor with a 12v coil.
75 Tips

I do not have a ballast resistor, only the RU-100 ceramic. With it being 1.2 ohms and my coil being 2.5 ohms, total resistance is 3.7 ohms. 12.5V/3.7 ohms = 3.4A, and I always assumed that was good based on recommendations I've seen in the forum. It's run like a top for 4 years with that set up. However, I can change it out for a ballast resistor. I have one that is 1.6 ohms.

I'm afraid I'll burn my coil up if I bypass the resistor. Is it OK to do that for a short period of time to see if the tractor runs better?

(quoted from post at 22:59:58 03/25/17)
I'm afraid I'll burn my coil up if I bypass the resistor. Is it OK to do that for a short period of time to see if the tractor runs better?

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yes, it's safe. the purpose of that extra resistor is to protect a [i:675b7cce99]six[/i:675b7cce99] volt coil from a [i:675b7cce99]twelve[/i:675b7cce99] volt electrical system. u have a 12 volt coil, it does not need that resistor's protection.

and for what it's worth, i have a 12 volt 2N with a 6 volt coil and no extra resistor. conventional wisdom says that in MY case, yes, i'll burn up the coil. thing is, it's had at least 100 hours put on it since i converted it to 12 volts... and that coil hasn't burnt up yet

whaNcock.......replace yer condenser. Its BAD!!! It takes about 5-mins fer BAD condenser to effect yer sparkies. Even brand NEW condensers are known to be BAD outta the box. While you've gottchur 4-nipple capple off, press open yer points (0.015) and stick the corner of $1-bill (cheap) between the points and PULL. Polish the INVISIBLE CORROSION from between the points. Simple, eh? Lets talk about yer 4-nipple frontmount coil. Ittza 6-volt coil that yer RU-100 converts 12-volts to 6-volts. So you gitt 12-volts when the points (0.015) are OPEN and 8.7-volts when the points are CLOSED. This simple electrical circuit stuff. Yeah, hear you on the weak sister keyed ignition switch. I replaced mine 3-times in 1-summer just brushhoggin' stuff. Gott gryped (PO'd) and went down to the local marine parts store and botta WATERPROOF toggle switch and have NO MORE problems. The OTHER thing you'll want to do, is to remove yer 2 8-in starter bolts and slip yer starter motor out about 1/2-in. SANDPAPER the gap fer better starter motor operation. 'stedda row-row, it'll go rumpa-rumpa. ........HTH, the amazed Dell

Guys...I really appreciate your feedback and suggestions. I made some progress today but am not 100% there. Since condensers are cheap, I had a new spare laying around and swapped out my recently installed, new one per Dell's suggestion not knowing whether it was actually good or bad.

Additionally, I noticed the brass nut was not at the 12 o'clock position. I don't know much about distributors other than what I've read in my tractor manual and read on this forum, and I don't recall seeing anything about that. Practically, I thought it looked suspicious, so I loosened the timing bolt on the distributor and moved the brass nut CCW a few degrees to 12 o'clock and then verified timing using Bruce (VA)'s timing jig and made sure my points were gapped properly (0.015").

Since it wasn't running good under load, I also confirmed my spark plug wires were connected correctly on the distributor cap by doing a continuity test from the plug to the cap. No issues there. (I was actually disappointed when I didn't find a problem thinking that a dumb mistake on my part would have been a very easy fix.)

I also thought I should check my spark plugs simply because I hadn't yet, and spark seems to be the issue. Upon removal, all four looked fine to me, and I used a wire brush on them by giving a few quick strokes on the metal pieces to polish them up. I don't think they are part of the issue, but I am wondering if I should change them out. Thoughts?

After all this, I restarted and it idled OK. Just seems to be coughing and sputtering a little more than I remember but nothing major. It's a little wet here, but I decided to try and plow anyway to see how it would do. Good news is I plowed 5-6 rows with no problem. I have a tight space to plow and sometimes have to reverse back to my starting point. In the past, I've been able to quickly throttle down to idle speed before backing up with no issues. Today, my tractor stalled a few times but that was quickly remedied by throttling up a tad.

Afterwards, I checked voltage and resistance a few places between the battery and the coil...didn't find anything irregular. Had 12.6V on the downside of my resistor at idle.

So, it appears I can plow, but my engine isn't purring like I'm used to. Remember, it was running like a top when I put it up last fall, and I've had zero issues for four years until a few weeks ago.

Any final suggestions???

" Additionally, I noticed the brass nut was not at the 12 o'clock position."

If the timing needs to be adjusted, the brass nut will not be at 12 o'clock.

" moved the brass nut CCW a few degrees to 12 o'clock and then verified timing using Bruce (VA)'s timing jig and made sure my points were gapped properly (0.015")."

Not sure I'm following you here....but, to set the timing, you need to set the point gap FIRST. Then, use TOH's jig or a straight edge w/ a drill bit to measure the 1/4" distance. IF you don't get the points to open at that precise measurement, THEN you move the plate.

" I am wondering if I should change them out. "

If the electrodes aren't rounded off, leave them be.

If you do this out of sequence, your timing will be off.

Will the gas drain out of the carb bowl in a steady stream and fill a pint jar in less than 2 minutes?

Tractor been sitting all winter? Drain the tank, add fresh gas. Then add the old gas back a gallon at a time.
75 Tips

You are right about the jig being from TOH! My mistake. I did verify the 0.015" gap first and then adjusted the timing. I've never had to adjust the timing on my tractor before. I bought the jig just in case I'd need to one day, and that day finally came!

I am getting proper gas flow from the plug on the bottom of the carb. Definitely can fill a pint jar in two minutes.

I did not drain the gas, but it only had a little in the tank from last fall, and I did add a significant amount of fresh gas before attempting to start a few weeks ago. I realize that's not the same thing as draining the tank and starting with new gas. Maybe performance will improve once I add more fresh gas and the old gas is used up.

I've also ordered a 0.6 ohm ballast resistor to replace the GU100 ceramic resistor. (It's the only resistor I have. I do not currently have a ballast resistor.) I'm uneasy about using no resistor at all, as suggested previously, even though I have a 2.5 ohm 12V coil. My GU100 measures 1.2 ohms, so less resistance will undoubtedly give me hotter sparks. Thing is, the GU100 has not hindered performance, as far as I can tell, the last four years.

Maybe I'm not setting the timing 100% correctly. I've studied the shop manual and TOH's instructions MANY times, but like I said before, this is the only distributor I've ever worked on. However, I feel like I'm following the instructions correctly. Maybe someone could suggest/post a YouTube video showing exactly how this is done!?!?

I've also ordered a 0.6 ohm ballast resistor to replace the GU100 ceramic resistor. (It's the only resistor I have. I do not currently have a ballast resistor.) I'm uneasy about using no resistor at all, as suggested previously, even though I have a 2.5 ohm 12V coil. My GU100 measures 1.2 ohms, so less resistance will undoubtedly give me hotter sparks. Thing is, the GU100 has not hindered performance, as far as I can tell, the last four years.

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i have been running a six volt coil with 12 volts for 5 years with less total resistance in the circuit than your coil provides. a test would do no harm, assuming the test lasts no longer than 5 years

as for why it hadn't affected your performance before? that could be said about most components that fail - "it used to work." it's possible that it has been slowly getting worse, and it finally crossed the line between good and bad.

I did bypass my GU100 resistor yesterday for about 3 minutes, and it didn't seem to make a significant impact. Although, I wasn't bypassing the resistor when I quickly throttled down and the engine stalled. Bypassing/no resistor might eliminate that. I will test it next time I'm out. Thanks for your feedback!

Here's an update. I'm a firm believer that most "it don't run/start" issues are spark related if one is able to get a steady stream of gas out of the carburetor bowl with the plug removed. In this case, I'd been able to get a spark to jump a 3/8" gap; checked the timing; replaced the points with high quality, Blue Streak brand, points and gapped them at 0.015"; read 12V at the top of the coil; and jumped the ignition switch and resistor with no significant improvement.

I finally decided to remove the carb, which I literally haven't touched during the 8 years I've owned my tractor, and clean it since choking did helped during the first 1-2 minutes of starting. I didn't give it a thorough cleaning, just a good spraying out with carb and choke cleaner. All I did was remove the 4 bolts and split the carb. No overnight soaking or anything like that.

When I got the carb back on, the tractor started up and ran with no choking just like last fall. Just goes to show that eliminating one thing at a time and moving to the next, most likely issue does work.

Thanks to everyone who commented on this posted and helped me along the way!!!