8N runs rough at idle and with the engine unloaded

PeterH

New User
I inherited a 1948 8N with a front mount distributor. Electrical system has been converted to 12volt and has a 12 volt coil.

engine was rebuilt in the mid 90's, run for a couple hours and then sitting ever since. (if I remember correctly the head was retorqued several times to ensure proper bolt torque. I have also retorqued the head after the first run, with no looseness noted

When cold, engine starts and runs good for about 5 minutes then begins to run extremely rough at idle and about 1/4 above idle. Have to pull the choke out slightly to keep it running. As RPM's increase, the engine runs a lot better and the choke can be pushed in. At full throttle the engine runs fairly well but has a slight sputter (no backfiring). Have noted that when the engine is loaded the the sputter stops from about half to full throttle and runs better at lower RPM's, but still needs a little choke at idle (loaded by simply applying the breaks enough to put a little strain on the engine). When the brakes are released, the sputter immediately comes back

the tractor currently has new plugs (properly gapped), new points (properly gapped and checked on 2 different occasions, along with timing), new condenser and new 12volt coil. There were some extra parts kicking around so I installed another coil and condenser to rule those out with no change). Also briefly jumped the ignition switch to rule that out, and briefly took out the coil resistor to check that... no change. spark plug cable installation / firing order has been confirmed, no issues. When spark plugs are removed they have a nice dry "tan" color which looks pretty good to me.

Checked the fuel system and gas flows from the carb drain plug without issue and all filters / strainers are clear. The carb was new when the engine was rebuilt... I have it apart now and soaking but all the components look very clean so i don't think that was the issue. Air cleaner has also been cleaned

I had already checked for carb / manifold leaks with a propane torch but did not note an improvement when propane was flowed around the flanges. Tried adjusting the idle mixture screw (currently 1 turn out) but no improvements

Compression dry is 115, 106, 116 and 118. Wet compression numbers went up a little bit (roughly 4 to 5 psi) indicating that the #2 cylinder probably does not have a valve issue, but is still weak compared to the others. Do not have any indication of a head gasket leak at this point. Also have checked valve clearances, intake and exhaust were in spec per the manual on all 4 cylinders

Any suggestions?? not a 8N tractor expert, so having a hard time figuring this out.

I have not removed the governor yet for inspection... but there is no "hunting" so I am not sure that is the problem either
 
Pete.........ya gotta BAD front mount coil. Thems BRAGGIN' compression numbers, even #2 at 106 is good. Specs call fer 90psi min. Most 4-nipple front mount dizzys points (0.015) are adjusted on the kitchen table. (seriously) Keep yer itchy-twitchy fingers off'n them handy-dandy carb tweek'ums. But you've already confessed to trying to adjust yer carbie (frown) Heres the WAY I recommend. Adjust the down-pointing main jet to 2-turns and LEAVITT!!! Adjust the side-pointing idlemix fer FASTEST idle NOT SMOOTHEST idle. Understand the difference? Usually ends up about 1/8-1/4 turn. BTW ennytime you have starting issues, replace yer sparkies, you've FLOODED them. Don't throw them away, just clean and dry them, one-atta-time in HOT running engine and save'um fer the next time (and there will be a NEXT time) Recommend AutoLite 437's gapped 0.025. ......HTH, yer sparkie-meister Dell

oh yeah, condensers seldom wear out but NEW points need the INVISIBLE corrosion POLISHED off by clampin' the corner of $1-bill (cheap) between the points and pulling
 
" Electrical system has been converted to 12volt and has a 12 volt coil."

What resistors are you using?
ballast_Bruce_zpsboeikaki.jpg

75 Tips
 
(quoted from post at 07:20:02 01/04/17) " Electrical system has been converted to 12volt and has a 12 volt coil."

What resistors are you using?
ballast_Bruce_zpsboeikaki.jpg



When I pulled it out of the tractor shed, was not sure exactly what coil it had (6-volt or 12-volt) and there was NO resistor connected. When this tractor last ran in the 90's I seem to remember it sputtering a bit, so when I noticed it did not have a resistor I figured that was one of the original problems, and bright a new resistor and new 12volt coil.

I ordered the 12volt coil from Steiner (ABC119) and also purchased the resister they recommended (ABC366). The specification states that it has roughly 1.5ohms resistance. So currently the only resistor connected is the 1.5ohm item I bought from Steiner and the new 12volt coil is currently installed.
 
Sorry, but I don't have a Steiner catalog.

Referencing the picture, which of those 2
resistors are you using? The OEM ballast
resistor or the white ceramic one?
75 Tips
 

in that case, try jumping around that ceramic resistor. it is only needed for a 6 volt coil in a 12 volt system. a 12 volt coil should not need it.
 

sorry, i missed where u said steiner's told u that ceramic resistor was needed. the gurus here can chime in, but in the meantime, my paltry knowledge says try it without, and see what happens.

for what it's worth, i am running a SIX volt coil with 12 volts and no ceramic resistor added, and have gotten away with it for 5 years now ;)

why no added ceramic resistor? my conversion kit came with one, but the tractor wouldn't fire with it. imagine my surprise, earlier this year, to learn that its resistance should have been much lower than what it was - namely, 3.5 ohms.
 

great, my last reply only shows in classic view. i'll try again (not holding my breath tho):

PostPosted: Wed Jan 04, 2017 11:32 am Post subject: Re: 8N runs rough at idle and with the engine unloaded

sorry, i missed where u said steiner's told u that ceramic resistor was needed. the gurus here can chime in, but in the meantime, my paltry knowledge says try it without, and see what happens.

for what it's worth, i am running a SIX volt coil with 12 volts and no ceramic resistor added, and have gotten away with it for 5 years now Wink

why no added ceramic resistor? my conversion kit came with one, but the tractor wouldn't fire with it. imagine my surprise, earlier this year, to learn that its resistance should have been much lower than what it was - namely, 3.5 ohms.
 
cec.......iff'n I remember correctly, they're 7/16 coarse thread, use BRASS NUTS and anti-seize, 26ft/lbs.......Dell
 
Steiner's sold you the wrong resistor.

Remove that resistor. It's a fixed resistor. You need ONLY the OEM ballast resistor. Buy it & install it. The ballast resistor is .3 cold & 1.7 ohms hot. That allows full current to the coil for starting but reduces the current as it heats up. (see tip # 30)

You can temporarily jump the ceramic resistor & run full current to the coil to see how it runs. But don't do it for very long.

Post back w/ results because it's not highly likely that the wrong resistor is causing your problem.
75 Tips
 
I jumped the resistor (probably ran it too long) but it did not make any difference and most likely damaged the coil as the tractor barely runs now and sounds like my John deere 420. Before I had good spark on all 4 cylinders, now have no spark in #1, poor spark in #2, and looks like good spark in 3 and 4.

Guess the next step is pull the distributor off, check points, order a new coil, OEM ballast resistor and check plug wires. when I get all that straightened out I expect to have the same problem as before... very poor running at or near idle and improved running at full speed but still not 100% correct


Any additional suggestions?
 
" I jumped the resistor (probably ran it too long) but it did not make any difference and most likely damaged the coil "

Probably not.

Replacing the plug wires and installing the OEM ballast resistor is a good idea. I'd also replace the rotor & cap. But I doubt you have a coil problem. A weak coil will give you a weak spark on all 4.

Time for a detailed check of the distributor.

The first thing you need to check is bushing wear. If the shaft has any sideways movement AT ALL, the bushings must be replaced.

Assuming that the bushings & advance weights are ok (*see below), & that you have correct voltage to the coil (battery voltage with the points open and about half that with the points closed), the most common electrical failure (no spark, weak spark) points on the front mount are:

1. The insulator under the brass concave head screw & where the copper
strip attaches. (it's fiber & will wear out; poke & prod w/ your meter leads to make sure it still works) If you need to replace the insulator, use a .250 x 3/8 nylon square nylon anchor nut available at most big box home stores



2. The pigtail at the bottom of the coil not making contact w/ the
concave head brass screw inside the distributor. (With the coil on, the pigtail must firmly contact the brass screw. No contact = no spark



3. The copper strip is broken or grounded to the plate. (look very
carefully for cracks & breaks).



4. The condenser wire grounding to the plate or side of the distributor.



5. The tab on the bottom of the coil not making contact w/ the brass
button on the cap. (With the cap on, the tab must firmly contact the brass button. No contact = no spark.)



6. Incorrect positioning of the spring clip on the plate causing the
pigtail to ground. (the open part of the clip goes between 7 & 9 o'clock on the plate. That puts the straight part of the clip opposite of the timing screw at 3 o'clock)



7. Incorrect seating of the coil on the distributor due to a loose bail
or no gasket.(the coil must not move at all; if it does, replace the gasket or bail. Or stick some cardboard under the bail).



8. Water/moisture inside the cap due to gasket failure or the absence of
a gasket. (the cap AND coil have gaskets)



9. Dirty/corroded/burned/incorrectly gapped or misaligned points. I use
only Wells, Blue Streak or Echlin brand points (* *see below). If you are using quality points and cannot get the gap to open to .015, chances are you need to replace the bushings. If the shaft has any sideways movement AT ALL, the bushings must be replaced.



10. Burned rotor, cracked/carbon tracked cap.



After find the problem & re-check the point gap, do a continuity check before you put the distributor back on the tractor. Before you start, make sure your meter/light works.



With the distributor still off the tractor, follow these steps:



1. Coil off, cap off, points open. One probe on the brass screw & the
other on both sides of the open points. On the side closest to the cam, you should have continuity. Not on the other side! If you do, you will also have continuity everywhere because the points are grounded.



2. Coil off, cap off, points open. One probe on the brass screw & the
other anywhere on the body of the distributor. You should have no continuity! Now, rotate the tang on the distributor....as the points open & close, you have continuity (closed) and lose it when they open.



3. Put the coil on the distributor, cap off, points open. One probe on
the lead on the top of the coil, the other on the cam side of the open points. You should have continuity!



4. Coil on, cap off, points open. One probe on the lead on the top of
the coil, the other anywhere on the body of the distributor. You should have no continuity!



At this point, I just put the distributor, coil & cap all back on the tractor as a unit. The reason I do this is because it is real easy to get the cap or coil misaligned trying to put it back together, one piece at a time. The result is something gets broken or you get a 'no spark' problem.



It's possible to put it back on wrong & break it. Look at the slot on the end of the cam shaft. Whatever angle it happens to be, turn the distributor tang to match it. Make sure you can tell the wide side from the narrow side on both the cam & distributor! (close counts). Place the distributor on the front of the engine, gently push it in place & slowly turn the distributor body until you feel the tang slip into the slot. Rotate the distributor body until the bolt holes line up. Hand tighten the two bolts until the distributor body is flush with the timing gear cover.



* Unscrew the plate hold down screw & remove the C clip to get the plate out. Remove the shaft & weights. The weights should freely move.



* *NAPA part numbers:



. Points: FD-6769X

. Condenser: FD-71

. Rotor: FD-104

. Cap: FD-126
75 Tips
 
Thanks for the detailed info. I am heading home now, but in the spring when I get back up to the old farm I will go through your list and complete all the suggestions. Hopefully I can get this tractor running well so I can find it a good home.

One question, so I know I have a quality spare 12-volt coil... do you have any suggestions on the best place to get them?
 

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