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Thread: John Deere 425 Engine Problem

  1. #1

    John Deere 425 Engine Problem

    20hp Kawasaki twin cylinder. Engine runs perfect for about 20 min. then will instantly start to spit, sputter, & puff black smoke. If I shut off deck & idler back it usually recovers. Start mowing again, then it will continue to happen on & off. It might run fine for 5min. or 20min. but continues to act up. Seems to set it off by going on an incline. Action so far, rebuilt carb & adjusted float. Tried to duplicate by removing one plug wire but it doesnt act the same.
    Any help would be greatly appreciated, Thank you! Farmboy

  2. #2

    Re: John Deere 425 Engine Problem

    Hi farmboy. I recently worked on a john deere 425 tractor with the same exact problem as you're having. It would start and run great for about 20 min. and then begin to cut out, skip, and lose power. After downloading a john deere tech. manual online,(for about 10.00 bucks), and scrutenizing it very carefully, I began testing proceedures and found the faulty part, replaced it and got it fixed. My problem turned out to be a faulty ignition module getting hot and not firing the left side coil. Some of the things I did before I started looking at the electrical end of things were to drain out the stale gas that was in the tank and replace it with fresh stuff, made sure the fuel pump was running and pumping sufficient amounts of gas out the gas supply hose at the filter, and made sure that the gas tank cap vent was not plugged and allowing a vacuum to be drawn on the tank. I did this by loosening the tank cap when the engine started to act up, which made no difference in the way it ran. The air filter was clean, carb throat looked very clean, and I could feel the carb shut off solenoid valve clicking on and off with the key switch. I finally began to suspect an electrical problem and began to check the wiring for any chaffing or rubbing which would cause a short, found none. I then went through the ignition system components and checked the resistance on the ign. coils, pulsers, and high tension leads. All checked out to be within spec. In order to know just what was up with the ign. end of things, I went to my local NAPA store and bought two in-line spark testers, hooked them inbetween the spark plug and high tension leads on both sides of the tractor. Now I could run the tractor and see just what the ign. system was doing. Sure enough, the left spark plug wasn't firing when it got up to operating temp. Using my digital multimeter, I backprobed the L. side pulser wires at the ign. module harness while the tractor was running,(with my meter set on the AC scale), and found it to be putting out a good signal to the ignition module to fire the coil, I even checked the other pulser coil and found it to have the same output AC signal as the left side was. I could then eliminate the left pulser coil as the culprit. The next thing I did was to swith the ign. coils and high tension leads from one side to the other and found that the problem did not transfere, it was still on the left side, I could then rule out the coils and high tension leads since they both worked on the right hand side. I also did the same thing with the spark plugs, no change. I knew that the left coil pos. terminal had battery voltage, but to be on the safe side, I installed a fused jumper wire from the pos. bat terminal at the starter to the pos spade connection at the L ign. coil,(disconnecting the harness wire there first), this made no change in the way it ran. I then could eliminate the time delay module because#1- it was feeding bat voltage to the ign. coils, and#2- it was energizing the ign. module to fire the coils,(allbeit only the right side fully, and the left side when engine temp. wasn't up there too bad). I then checked the ign. coil wires to make sure that they were not grounded or shorted and found them to be in good shape. So, by process of elimination, came to the conclusion that the ign. module,(john deere calls it an ignitor), was not firing the left side coil when the engine temp.,(and therefore the module temp.), was hot. After taking a big gulp and swollowing hard, I plunked down 275.00 plus tax at my local deere dealer and bought the ign. module. Guess what- she runs like a new tractor now. Hope this helps you out farmboy. Some afterthoughts--- it helps to be in a very shaded spot when trying to observe the in-line ignition testers because they use a bulb instead of a gap that the spark jumps across. It also is very important to understand how the system works before attempting any troubleshooting. I wound up burning a CD when i downloaded that tech manual, there was soo much information that trying to print it all out on paper would be bulky and cost ineffective.

  3. #3

    Re: John Deere 425 Engine Problem

    Think you have to go back and check the carb again. Black smoke indicates it is running rich. You said that the inclines set it off. If you haven't done so I would replace the float needle and seat. Sounds like they are not seating properly and maybe the float is starting to go.

  4. #4

    Re: John Deere 425 Engine Problem

    I agree that this could indeed be a carb problem. However, the problem that I was experincing with this particular john deere 425 was indeed being agrivated by mowing on an incline, (now I don,t have any idea why this was), but it was. I forgot to tell farmboy that before I started looking at the electrical end of things, I also checked and set the valve clearance and cheked engine compression, thinking that if valve clearance was too tight that when it warmed up, valve clearance would close up and cause rough running . Also, the left side spark cut out completely, which would cause raw gas to wash the cylinder wall down and blow out the exhaust. Black smoke is just that- raw fuel not burned completely. I didn't see too much black smoke, but experienced a heavy gas odor. If compression is good and the in-line spark checkers indicate good spark durring rough running, then one would certainly expect carb problems. I'm not saying that this is farmboy's problem, I'm just relating my experirnce. Thanks for your input.

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