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Subject: 8N running rough

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Jeff    Posted 06-30-2018 at 15:56:09 [URL] [DELETE]        [Reply] [Email]  
  • 8N running rough
  • Gents, I need some help. I have a couple hours of seat time on my recently acquired '48 8N. My dad said it "misses" and has done so for years. He chased the problem with a carb rebuild kit in 2015 and a rebuild kit (3-8T-010?) performed by Norther KY tractor & equip in 1999. I'm not sure what kit that is but it looks like new dist wires were installed also.

    I'm not sure that it's miss firing but I can describe the sound as an intermittent popping. Not loud like a backfire, but a soft puff at any RPM range. Could be a miss fire I suppose. The condition is worse when the choke is fully off. It runs smoother with the choke held out about 1/4 inch.

    I was running a blade today and it started running worse than usual, sputtering and running really rough like it was going to stall. It would rev and sputter out repeatedly as the governor pulled and released on the carb linkage. It seemed to smooth out if I held the choke out even further! After trying to run it that way, it would run rough again so I'd push the choke back in to the original 1/4 inch out using clothing pins on the choke stem. I also screwed the final mixture screw out a little which seems to smooth things out, but not sure if that was the problem.

    Strange thing is, it started running smooth again for reasons unknown. Smoother than I'd ever seen before without any of the popping or missing I previously described. Still with the choke held out 1/4 inch. HUH? How can it run like crap and then run perfect?

    To top things off I parked it, shut if off, and then decided to park it elsewhere. DEAD BATTERY! In retrospect, I don't think the voltmeter increases/decreased with engine RPM. It only increases slightly when the ignition is switched on and stays there. Shouldn't it change with RPM's? Checked the belt, it's tight. The battery is a 2015. Connections all seem tight.

    Another thing, there is no throttle response in the first 1/4 to 1/2 of the throttle quadrant. governor spring isn't really loose but isn't so stiff it can't be turned in the I also noticed it would pull back slightly from the end of the quadrant when running at wide open throttle. Any ideas? Thank you all in advance. I really want to get this thing purring like a kitten. I really like it and want to keep it alive for my grandpa, the original owner.

    Tim Daley(MI)    Posted 06-30-2018 at 19:59:29 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N running rough
  • I see a few things that matter, and a few that don't. First, you say it is a '48 8N so we can assume it is a front mount distributor, However, you don't tell us if it is a 6V/POS GRN setup or a 12V/NEG GRN switch over job. That is an important detail you left out. Bear in mind that whether it's a 6V/POS GRN or 12V/NEG GRN system, if it isn't wired correctly, it ain't gonna work right. Most problems like you have are due to poor/incorrect wiring jobs. I suspect you have a bung-hole/rats nest/cobbled up wiring job and that is part of your root cause problem.Next, most quality carb rebuild kits are fine, example is TISCO. We really don't need to know a part number or who supplied it. So your dad bought a carb kit and traced the backfiring then to a carb rebuild, yet the problem persists and has done so for years. What is a ' (3-8-010) by Northern KY 'rebuild kit' that "...looks like new dist wires were installed also..."? Is it possible that you have a12V switchover job and there is an alternator now AND/OR in addition to 12V an EI (Electronic Ignition) System was added too? Cheap batteries can be junk out the door of Wally World o r your local auto parts store. Get the battery tested at your trusty local starter/alternator shop. Purchased in 2015 means nothing. The battery must sustain a charge under load. Charging it doesn't mean it is good. You say 'VOLTMETER', so that triggers another 12V thought on my part. Some fellas take the original AMMETER out on 12-volt conversions and install a voltmeter. ALL new Ford Tractors from 1939-1959 used an AMMETER, 6V/POS GRN system with a generator and a round-can cutout on 39-47 models, and a voltage regulator after 1947. Again, which do you have? A generator or alternator? You won't see any significant ammeter movement when revving the engine up. If you want to test the AMMETER, pull the light switch 'ON' and observe if the needle drops to 0(ZERO) or even a bit to the minus (-) side. Forget the governor for now. You have other issues to deal with and I'd first suspect your wiring system is all mucked up. The carb may need to be rebuilt correctly, but mo more buying any new parts until you do a root cause problem solving procedure. Get out your 8N essential manuals and read thoroughly. You need 3 things to run: Fuel, Spark, and Compression. Concentrate on the first two for now and you'll most likely discover the root cause or causes. Perform a fuel flow test on the carb, ENGINE COLD, NO POWER. Fix any problems then move on to spark. While battery is in the shop, go thru the entire wiring. You want to confirm the wiring is correct, and NO POWER to do this either. You trace wires by continuity, not colors. Go to our HOW-TO's forum, ELECTRICAL, and download a copy of "WIRING PICTOGRAMS by JMOR". Start with the basics. You want to make your grandpa proud don't you?


    Tim Daley(MI)

    Jeff    Posted 06-30-2018 at 21:03:31 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N running rough
  • Yes, front mount with a 6V negative ground system. The part number was for a rebuild kit installed in 99. It was $437 dollars so must have been a bit more than some gaskets and wires but I'm not sure what was included. Dad forgets. I misspoke when I said Voltmeter. It's definitely reads AMPS, I just checked. Uses a generator as well, not an alternator. As far as testing the ammeter, It doesn't have lights so I can't test that way. Regarding fuel, spark, and compression. Just tonight I drained the gas tank and checked all 3 screens. The screen in the tank on the fuel bowl stem was non existent. The screen directly above the glass bowl was clean. The screen at the carb inlet was hardly dirty. Fuel flow prior to taking it apart, from the carb drain bolt, appeared to be good. But with my lack of experience I couldn't tell you what was adequate or not. I haven't checked spark or compression yet. Those will be next. I'll have to check wiring also to be sure. Thank you for your help, sir.

    Bruce (VA)    Posted 07-01-2018 at 08:46:01 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N running rough
  • OK, we're making progress.

    You have good gas and clean screens. Remove the bolt in the bottom of the carb bowl; w/ the gas turned on, the flow should fill pint jar in under 2 minutes.

    While that does not eliminate a carb problem, it appears that your more pressing need is a tune up.

    You need to replace the points, plugs, condenser, rotor & cap and set the timing. See tips 39 & 40. As well as tips 66, 67 & 68. This is a 70 year old tractor. It needs far more attention than any new vehicle.

    The front distributor on the N tractors may be a bit of a surprise & mystery to some folks, but it was the norm on V-8 Ford cars and trucks from 1932 to 1948.

    The front distributor was designed to come off of the tractor to replace/adjust the points. To do this, remove the wire on the coil, remove the coil bail, remove the distributor cap & take the two bolts off. The base of the distributor has an offset tang & can only go back one way unless you really force it on.

    The first thing you need to check is bushing wear. If the shaft has any sideways movement AT ALL, the bushings must be replaced. (see Note 1, below) Next, if this is the first time you have had the distributor off the tractor, make sure the advance weights are in working order. (See Note 2, below)

    Next, look at how the points & condenser are set in the distributor before you start pulling it down! Turn the tang & observe how the points open & close. If this is your first time doing it, draw a sketch! Make sure you are using quality points. I use only Wells, Blue Streak or Echlin brand points (See Note 3, below). Be careful not to ground the tip of the condenser wire to the body of the distributor when you replace the points. Do not break the little copper strip that go to the points. (If you do, make another out of the old set of points). Check the insulator w/ your meter. If it's bad, replace it with a Hillman Group square .375 license plate screw, Item # 138916, model #881189. Also, make sure the condenser wire does not go through the same opening in the distributor as the coil pig tail. The condenser wire goes through the opening on the top right.

    Look at the old points; are they burned, pitted or misaligned? Check the point gap, .015 on all four lobes. Make sure the blade is at a perfect right angle to the points. You want to feel just the slightest bit of drag when you pull the blade through the points. Set the points on the high side of the cam and ensure they align correctly. Make sure you have the star washers under the screws on the points. If you need to replace the 8-32 X.19 fillister head screws, ensure that the new screws do not interfere with the advance weights. Dress the points by running a piece of card stock or a brown paper bag through them. New points sometimes have an anti-corrosive dielectric coating on them & old points can corrode or pick up grease from a dirty feeler gauge or excessive cam lubricant. And, don’t forget to lube the rubbing block w/ cam lube; not Vaseline, not bearing grease, but cam lube . (See Note 3, below).

    If you are using quality points and cannot get the gap to open to .015, chances are you need to replace the bushings. (See Note 2, below)

    Now, set the timing. Get a meter or test light, a 21/64” drill bit (See Note 4, below) & a metal straight edge. Put the distributor face down w/ the condenser on the left & the timing plate lock screw on the bottom. Look at the end of the shaft: it has a narrow side & a wide side. Make sure you can tell the difference. Now, place the drill bit in the bottom mounting hole (this will be your reference point for measuring). Next, place a straight edge on the wide side of the tang on the shaft as shown in fig. FO83 in the picture. Rotate the shaft CCW (as viewed from rotor side OR CW as viewed from back/tang side) until the straight edge is ¼" beyond the outside edge of the drill bit you stuck in the distributor mounting hole. At this distance, the distributor points should start to open (get your meter/light out now & check). If not, loosen the timing plate lock screw and turn to advance or retard the timing (move the plate down to advance timing, up to retard). Remember, each one of those little hash marks represents about 4° of timing. Keep adjusting until you get the proper ¼" setting. (if the plate won’t move, you might need to remove the big C clip to loosen it a bit) As you’re adjusting, eliminate backlash by turning the shaft backwards (CW as viewed from the front) and bring the shaft forward (CCW as viewed from the front) to measure your setting. This ¼" setting will get you static timing at top dead center.

    After you set the points & timing, do a continuity check before you put the distributor back on the tractor. Do not skip this step! 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.

    Double-check your firing order & plug wires. It’s 1-2-4-3, counterclockwise. It’s very easy to cross 3 & 4 both at the cap and on the head.

    And finally, do not forget to remove the distributor on at least an annual basis (more often, depending on use) to check the point gap and re-lube the cam.

    Note 1: Unscrew the plate hold down screw & remove the C clip to get the plate out. Remove the shaft & weights. The weights should freely move.

    Note 2: There are three ways to replace the bushings in a front distributor:

    1. Buy new bushings (part numbers 9N12120 front & 18-12132 rear). Press out the old ones, press in the new ones and ream to fit. CAUTION: do not try this unless you have a press & know how to use it. If you break the base, a new one costs $130. If you bend the tower which holds the front bushing, a new plate will cost you $30.

    2. Take the new bushings and distributor to your local machine shop.

    3. Send the distributor out for bushing replacement if you do not have a
    local machine shop.

    Make sure your distributor isn’t worn out; check the wear parts with a micrometer and compare what you have to the factory specs (below).

    Factory Specs:

    Shaft top .4367 / .4370

    Shaft Bottom .8625 / .8630

    Cam Flats .789 / .791

    Cam Lobes .869 / .871

    Base Tang .177 / .178

    Note 3: NAPA part numbers:

    · Points: FD-6769X or ECH CS35

    · Condenser: FD-71 or ECH FA200

    · Rotor: FD-104 or ECH FA 300

    · Cap: FD-126 or ECH FA 350

    Note 3: Yesterday's Tractor kit:

    Premium Blue Streak points (A0NN12107ABS), rotor, condenser, and gauge Part
    No: APN12000ABSR

    Note 3: Just8N's kit:

    Heavy-Duty Point Set, Condenser, Heavy-Duty Rotor, Heat Range Matched Spark Plugs. Packed 6 to Master Carton. Contains: 1-9N12107 Point Set, 1-AONN12300A Condenser, 1-9N12200 Rotor,1-9N12104 Gasket Kit,4-AL437 Spark
    Plug,1-015 Gauge, 1-025 Gauge.

    Note 3: Distributor cam lube NAPA:


    Note 4: Rather than the drill bit, a jig made by Dan Allen (The Old Hokie) will make this task quicker & more accurate.


    Jeff    Posted 07-04-2018 at 06:53:03 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N running rough
  • Bruce, I finally got around to servicing the distributor. Problem was, NAPA ordered the wrong parts so I was unable to replace the condenser, points and rotor. One of the first things I noticed was that the points were nowhere near .015 apart in the open position. I really thought I was onto something there and decided to go ahead and re-gap the points and put it all back together. Checked for continuity as you described and timed it perfectly once I figured out what the hell they were talking about. Unfortunately this didn't fix the issue. The points and rotor looked to be in good condition, condenser I couldn't test. My dad said he replaced these items years ago but hardly used the tractor since then which is why everything still looked good. So as it stands the tractor still has that slight puff or miss sound while running and needs to have the choke pulled out slightly to run smoother. I will say it's mostly in the low RPM/idle range.

    Here's another piece to the puzzle, and this may or may not be related the above mentioned issue. Whenever I use the tractor in the field, grading with a box blade in my case, it will go from running as previously described to running really, really crappy. Like sputtering and hardly running. This usually happens after about an hour or so. What I discovered, by chance, is that if I snap the throttle to wide open and back down to idle quickly it will run normally or at least what is considered normal for this tractor. This leads me to believe the governor is influencing the carb in a negative way and the "snapping" of the throttle is resetting the linkages. If so, I can only hope that the governor is the overall cause of my issues to include the need to hold the choke out slightly to run better. What do you think? Is the governor capable of such mayhem? Also, I pulled the carb and inspected each part. I also made sure each and every passage, according to diagrams on this website, were clean and clear which they were. All parts were in great condition, again because they were replaced but hardly used. I then replaced the gaskets.

    Jeff    Posted 07-01-2018 at 19:04:26 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N running rough
  • Thank you for this informative post. I have not performed the tuneup yet but I can say at this point that I have good fuel flow, consistent spark regardless of the stumbling condition if I let the choke go all the way in, and all wiring is correct verified by continuity testing. I just checked the entire wiring harness and compared it to JMOR's wiring pictograms. The only difference is this tractor was switched to a Negative ground. Why would that be? What's the point? Should I just go ahead and switch back to positive? As far as I can tell it's as simple as grounding the positive cable and running the negative to the solenoid connection. Am I missing something here? Will I have to re-polarize the generator if I switch?

    Jack - Iowa    Posted 07-02-2018 at 07:08:18 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N running rough
  • It's not worth your time to switch back. Technically the electrons flow easier one direction than they do the other. However you will see no difference in your tractor's operation. Perhaps on a real high performance engine. You would have to re-polarize the generator if you did.

    Tim Daley(MI)    Posted 07-01-2018 at 07:40:26 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N running rough
  • Jeff-
    These N's will run on positive or negative ground, 6V or 12V but all old Fords were designed on the 6V/POS GRN system -it is a technical design based on electron flow -positive ground gives better flow to spark plugs. You say you do have generator, okay, do you also have a voltage regulator? If so, what does it look like and where is it located? The generator must be polarized to operate on whatever your choice is. If you had it 6V/POS GRN and installed a new battery as NEG GRN, the genny will not spin right. If your AMMETER is the original induction 'loop' style, you can test with a simple circuit and your (good) battery or sweep a magnet over the faceplate and see if the needle moves. If you have a distributor that negates an EI. $437 seems an enormous amount unless, everything was replaced -distributor, wiring, voltage regulator, and possibly coil and plugs and maybe more. The fuel flow test should be performed before removing and/or replacing the Sediment Bulb and/or screens. With engine COLD, Sediment Bulb valve CLOSED, loosen and remove the NPT drain plug on the bottom of the carb. be sure to have a container below to catch the fuel in. Now open the Sediment Bulb Fuel Valve 2 Full turns only. Fuel flow thru the drain port should be a steady stream and fill a pint jar in 2 minutes. If so you are fine. If not, close valve and replace the drain plug. Next, go to the carb fuel inlet brass elbow and with a 7/16" Flare Nut Wrench, a standard 7/16 open end or Crescent Wrench will work but NO pliers, Channel Locks, or Vise Grips. Loosen the fuel line coming from the Sediment Bulb. Slip the line with the fitting up over the elbow and point the fuel line down into the container. Now open the Fuel Valve 2 Full Turns only. Observe if the fuel flow is an almost pencil-thick stream, unobstructed, with no hesitation, sputtering, stopping and starting. If flow is sufficient, no problems with your fuel flow. Close valve, and at this point it wouldn't hurt to remove and clean the brass elbow inlet. It has a fine mesh screen attached at the end, the last of three inline screens in the system. Note the carb has an NPT tapped port for the brass elbow fuel inlet. DO NOT ATTEMPT to clean the threads with anything but the correct NPT tap. The brass elbow has, as does the Sediment Bulb fuel out port and fuel valve port a special thread too -it is industry standard for brake and fuel lines at 7/16"-24 UNS. Any attempt to chase the threads with the wrong tap or die would be disastrous. If you don't know, leave it alone. As I said, forget compression for now. You must have fuel and spark first and chances are there-in lies your problems. If you think you have good fuel flow, then spark is next. If no spark, now it's time to do a thorough system verification of the entire wiring and components. That is where I'm leaning to as your root cause problem.

    Tim Daley(MI)

    Jeff    Posted 07-01-2018 at 18:59:46 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N running rough
  • I just checked the entire wiring harness and compared it to JMOR's wiring pictograms. I also checked all connections for continuity. Everything is in order.The only difference is this tractor was switched to a Negative ground. Why would that be? What's the point? Should I just go ahead and switch back to positive? As far as I can tell it's as simple as grounding the positive cable and running the negative to the solenoid connection. Am I missing something here? Will I have to re-polarize the generator if I switch?

    Bruce Haynes    Posted 07-01-2018 at 20:53:04 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N running rough
  • Someone just hooked it up backwards. Switch it if you like; won't really make any noticeable difference. Polarize the generator if you switch it; see tip # 23.

    Do the tune-up & set the timing; post back w/ results.

    Jeff    Posted 07-01-2018 at 16:50:10 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N running rough
  • I checked the spark today. Each wire fires consistently even when I let the choke go in all the way which causes the engine to run rough and stumble. This rough condition does not affect the spark.

    Jeff    Posted 07-01-2018 at 08:14:40 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N running rough
  • Thank you Tim. I've determined fuel flow is good. I'll check for spark today and report back

    Jack - Iowa    Posted 07-01-2018 at 07:05:05 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N running rough
  • From the factory that was a Positive Ground system. Unless your generator has been re-polarized, it will not be working.

    Jeff    Posted 07-01-2018 at 08:19:31 [URL] [DELETE]        [Reply] [No Email]  
  • Re: 8N running rough
  • It was switched to a negative ground many years ago. There were no charging issues until now. But it mostly sat for the past 10 years only started up an ran every few months to "keep it running"

    Bruce (VA)    Posted 06-30-2018 at 18:28:16 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N running rough
  • It's nearly July; do you have any gas left in it from the winter? Using fuel stabilizer?

    When is the last time you replaced the points, plugs, condenser, rotor & cap and set the timing?

    Re the battery, see tip # 49.

    Check your generator w/ a meter; see tip # 47. Should be 7.5 volts if it's a 6v system.

    Re throttle response, see tip # 14.

    Jeff    Posted 06-30-2018 at 20:38:43 [URL] [DELETE]        [Reply] [Email]  
  • Re: 8N running rough
  • Fresh gas with stabil 360 added. Not sure about points, plugs, rotor, cap, condenser but my dad said some of those items like the wires, plugs, and cap were replaced not long before he stopped using it. That could be every bit of 10 years ago though. Don't know about timing either, how do you check and set the timing?

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