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Small gasoline engine fuel problem, quits running

Discussion in 'Shop Talk' started by willie59, May 14, 2020.

  1. willie59

    willie59 Super Moderator

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    Ok, not necessarily heavy equipment, but I ran across a problem I've never seen before and thought it was interesting. Maybe some out there are aware of this, I've just never seen it. Since I'm now working at a steel fabrication and erection shop, one of the things I work on are Miller Bobcat welders, a freaking pile of them! Kohler Commander V twin gasoline engines. One showed up in my work area with a tag on top "can't keep welder running". Hmm.

    Fire it up, lit up just fine. Started burning some sticky rods, after a few minutes, sure enough, it died. Hmm, sounds like a fuel problem. Changed fuel filter. Nope. Hmm, possibly the pulse pump, put a new one on it. Nope. Hmm. Maybe problem with pickup tube inside tank. Pulled it out, all good there. Pulled top of of the carb to check inside, all tidy. Maybe the anti-diesel solenoid on the carb is losing power, put a 12V jumper to it straight from starter. Nope. Hmm. Maybe anti-diesel solenoid is going bad, changed it with one from my parts pile, nope. Hmmm. Damn...I've done everything, what's left?

    That's when I recalled that some engines like this monitor oil pressure and will shut the engine down if it senses low pressure. Don't know if these engines do but I've check everything else. Well maybe it's just low on oil. Pulled the dipstick. No, not low...overfilled! What??? I marked the stick where the oil level was, held it beside the tube to gauge where the oil level was inside the engine, it was about 1 1/2" below the center of the crankshaft. Then it hit me, the thing I've never seen before as most folks don't overfill their oil sump, is it possible?

    I know these pulse fuel pumps work from the changes in crankcase pressure from the pistons moving up and down and those pulses of pressure is what makes them operate and pump. But that's with a proper oil level with oil remaining pretty much flat in the bottom of the sump. But with the oil filled to 1 1/2" below the center of the crankshaft, that would mean the lobes of the crank are slapping that oil in the sump all over the place inside the engine. Could this be disturbing the normal crankcase pressure inside the engine affecting the fuel pump? Drained the oil to the proper level on the stick, fired it off, burned rod after rod after rod, ran flawlessly. Well I'll be damned, learned something new today, overfilling oil sump on a small engine with a pulse pump will shut it down because it wacks out the internal pressure that operates the pump. Never seen that before.
     
  2. kenh

    kenh Well-Known Member

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    Sick ignition coil will have the same symptoms, after cool down they will run again, for awhile then repeat
     
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  3. willie59

    willie59 Super Moderator

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    My experience with these engines, two magneto coils, if one goes dead it's pretty easy to tell. I wager both magneto coils going bad at the same time is pretty rare, but not impossible. ;)
     
  4. grandpa

    grandpa Senior Member

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    Well let that be a good lesson to you you old scissorbill!!! Your never too old to learn sumpton!!!! Thanks for sharing.
     
  5. kenh

    kenh Well-Known Member

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    Two coils ? How old is this thing?
    Should have a new electronic system so one would have many choices on what to replace.:eek:
     
  6. John C.

    John C. Senior Member

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    Great tip. I doubt I would have thought of that. I've wondered how the little fuel pump setups work.

    I had someone over fill a lawnmower engine crankcase and the owner claimed the engine was burning up. I learned they now have positive crankcase ventilation systems. The mist and crankcase pressure blows the excess oil directly into the intake. The smoke does keep the mosquitos down.
     
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  7. petepilot

    petepilot Senior Member

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    willie. do you ever run into a Hobart welder with the same engine ? if you do I have a question for you .
     
  8. willie59

    willie59 Super Moderator

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    Of course I'm never too old to learn sumton you old weathered barn plank. LMAO :p
     
  9. willie59

    willie59 Super Moderator

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    These Kohler V twin engines are late model engines, still made old school with magneto ignition coils, one coil for each cylinder.
     
  10. willie59

    willie59 Super Moderator

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    Haven't done a Hobart, how old is it? I'm pretty sure the newer Hobart machines are made by Miller.
     
  11. petepilot

    petepilot Senior Member

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    this would be about 92 93
     
  12. willie59

    willie59 Super Moderator

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    Well, a bit of age with that machine, what's it doing?
     
  13. petepilot

    petepilot Senior Member

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    the fact that they are now made by miller is part of my problem . the auto idle board gave up and miller does not supply parts for the older mach. have had the board repaired then found another prob. the mach blows the fuse in the charging sys. as soon as I replace it although it still keeps the batt. charged the fuse goes whether the motor is runnin or not. I have not reinstalled the auto id. board not wanting to blow it again. this is what the question was have you ran into anything like this -----and I do not have the book anymore
     
  14. willie59

    willie59 Super Moderator

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    Oh man, you had to get me started on this. This is a beef I've had with Miller for what seems like a hunerd years, back into the 70's for sure, that is, controlling an idle solenoid with a PCB (printed circuit board). Circuit boards are a wonderful thing, but one thing they don't tolerate is amperage, and one thing that solenoids do is pull amperage, even in normal operation, but most definitely when they are losing their smoke. Result...fried circuit board! Not long ago I sent my local Miller distributor a, let's say, passionate email about this very subject and begged him to forward it to his Miller contacts as they REALLY NEED TO GET THEIR HEAD OUT OF THEIR A$$ ABOUT THIS PROBLEM. It's even worse with the newer machines, such as the machines we have, and we have a pile of them, the Miller Bobcat 250. On older machines, such as yours, the idle control had it's own circuit board. If it goes up in smoke, replace the circuit board, but now not an option for you. The newer machines, the Hour Meter "is" the circuit board. When the idle solenoid causes a problem it fries the hour meter. Great, now I have to replace the hour meter, which means I've lost the "accumulated hours" on the machine when I install a new meter because it's zero. Grrrrrrr. Simple solution, for you, me, and freaking Miller if I could just get them to do it, a Bosch cube relay. Again, circuit boards don't like amperage. Then install a cube relay. I've done this on a couple of our machines already, but we have like 50 of them, gonna take some time for me to modify all of them. Mount the relay near the starter, run a 14 gauge wire from battery terminal of starter to terminal 30 of relay with a 20 amp inline fuse. Run a 14 ga wire from terminal 87 of relay to the idle solenoid. Take wire that originally went to the idle solenoid and connect it to terminal 86 of the relay, then ground terminal 85 of the relay. Now you can go ahead and install your repaired idle circuit board with confidence that the idle solenoid will never fry it again under any circumstances, the relay becomes a firewall between the solenoid and the circuit board, no more fried circuit boards. As for your charging system problem, I have no advice there. sounds like you got a short somewhere blowing the fuse, but I have no clue what to tell you there.
     
    Last edited: May 17, 2020
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  15. Cmark

    Cmark Senior Member

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    Oh wow. I've had a Bobcat 250 for about 15 years and it's been super reliable. You've got me worried now. Hope you haven't jinxed it :)
     
  16. willie59

    willie59 Super Moderator

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    Doesn't happen to all of them Cmark, they (the machines) just pic and choose which ones this happens to, no rhyme or reason. Again, I've seen this in machines going back into the 70's. The common problem I see is circuit boards controlling solenoids, in this case idle solenoids. I'm sorry, circuit boards don't like amperage and that's one thing that solenoids require. It's a stupid concept doing this. A circuit board should control relays, not solenoids.
     
    Last edited: May 17, 2020
  17. petepilot

    petepilot Senior Member

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    that prob has me chasin my tail also can`t find any thing shorted or bare or broken wires . welder runs & welds great but it urks me to have it sittin running at speed when not burning a rod. am trying to come up with a manual for that year but not yet.
     
  18. willie59

    willie59 Super Moderator

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    Install a relay like I posted and you can go ahead and install your repaired circuit board, no worries, you won't fry another circuit board. Your charging problem is a different issue, can't help much with that without a diagram.
     
  19. petepilot

    petepilot Senior Member

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    if I can determine that there is no connection between the two problems I am going to try you`re fix and see what happens
     
  20. petepilot

    petepilot Senior Member

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    may get a chance to try you`re repair idea this weekend