Bad coil maybe???

3827 Views 18 Replies 7 Participants Last post by GT_80, Oct 19, 2010

DrDave1958

Discussion Starter · Oct 11, 2010

My 2000 DLT (917.272190) has a Briggs 25HP Intek and yesterday my wife ran it out of gas, so after I filled it, I drove it back up to the house and noticed it wasn't running right. It sounded like it was intermittently missing so I put in new plugs but that didn't help. I pulled the cowling and found a mouse nest on the right side and cleaned that out thinking it may have gotten hot and that's what was causing it to miss. Nope. Soooo, I pulled the plug wire off of the right side first (while the tractor was running about 1/2 throttle) and got a good shock. Turns out my rubber handled pliers have a small crack LOL. Well the tractor didn't sound much different than with the plug wire on so I figured I had my culprit, but just to be sure, I reinstalled the right wire and pulled the left wire off (After first wrapping the handles with electrical tape). Bingo. But to my surprise the tractor didn't die, it instead sounded like an old hit-and-miss engine where it would fire for 3 or 4 revs, then not fire for 3 or 4 revs. It continued to do this until I shut it off.

To my question: Could the coil be going bad or is it something else?
I haven't had time to tear into it yet, but I first plan to remove the coil and sand all the rust off of it and the flywheel magnets, then re-install with the proper gap to see if that will help.

Any other suggestions?

Thanks,
Dave

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1 - 19 of 19 Posts

oatville

· #2 · Oct 11, 2010 (Edited)

Here's some ideas (after you eliminate any obvious ones like low fuel, or leaning off the seat killing the safety switch, etc.)

1. Higher compression requires higher spark voltage. A marginal coil may produce just enough voltage to fire a plug at low speed but as the engine speeds up and compression pressure increases the coil may be so weak the plug does not fire, until the engine slows down again.

2. You could have a loose wire rubbing, shorting the magneto as the engine revs up and shakes, then...as it slows down again the wire doesn't touch and allows the Magneto to make spark again. Could possibly be internal with the coil. There should be a wire coming out of the magneto coil, short to ground to kill spark. Disconnect the wire from the wiring harness to elminate shorts anywhere in the circuit. Also inspect the spark plug wire for any worn spots it could be arcing.

3. I'm also thinking that a bad Valve lifter is "pumping up" and leaving a valve open at high RPM or a weak/broken valve spring? Just a thought.

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NEWT92

· #3 · Oct 11, 2010

Dave, my 797 done about the same thing this summer. One coil was bad the other weak. Replaced both and it runs like new. :fing32:

DrDave1958

Discussion Starter · #4 · Oct 13, 2010

Re: Bad coil maybe??? UPDATE

I tore into it last night and have pretty much ruled out the bad coil theory.
Here are the new symptoms:
(Note, left and right are from the drivers perspective)
With the engine running and the left plug wire on and right plug wire off, engine runs smooth.
With the engine running and the right plug wire on and left plug wire off, engine surges up and down until the choke is pulled out about half, then engine runs smooth. Which says to me the right side is getting too much air or not enough fuel.

My thinking is one of the following:
a) Intake valve
b) Intake manifold gasket
c) ????

Any ideas appreciated.

Thanks,
Dave

P.S. I've been looking for an online manual for adjusting the valves procedures but haven't found anything so far, if anyone has a link that would be great. I forgot to get the engine model number last night, but according to sears parts direct it should be 445777-0129 E1. It's a 25HP Briggs I/C Platinum Intek.
The tractor is 917.272190 s/n100600A004915

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GT_80

· #5 · Oct 13, 2010

briggs website has almost all of it's repair manuals for it's engines for free.

DrDave1958

Discussion Starter · #6 · Oct 13, 2010

GT_80 said:
briggs website has almost all of it's repair manuals for it's engines for free.

Yea I tried that first but they only show an IPB and operators manual.

oatville

· #7 · Oct 13, 2010

Re: Bad coil maybe??? UPDATE

If your really a Doctor your time is too valuable to waste working on a tractor, pay a shop or offer free medical advice to find out whats wrong it then decide to fix it yourself or have them do it in exchange for a free check-up and basic lab tests or, if your Vet, shots for their Dog.

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jroy

· #8 · Oct 13, 2010

Re: Bad coil maybe??? UPDATE

oatville said:
If your really a Doctor your time is too valuable to waste working on a tractor, pay a shop or offer free medical advice to find out whats wrong it then decide to fix it yourself or have them do it in exchange for a free check-up and basic lab tests or, if your Vet, shots for their Dog.

Or he can do what ever he wants to. Working on tractors is a hobby for some people, not everyone that works on their own tractors does so because they can't afford to have someone else do it. Would you prefer he drop it off at the shop and go home and watch tv?

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oatville

· #9 · Oct 13, 2010

Re: Bad coil maybe??? UPDATE

jroy said:
Or he can do what ever he wants to. Working on tractors is a hobby for some people, not everyone that works on their own tractors does so because they can't afford to have someone else do it. Would you prefer he drop it off at the shop and go home and watch tv?

Watch TV? of course not, everyone knows good doctors don't have time to waste sitting around watching TV! Maybe he could do some breast exams while someone goes over his tractor for him. Imagine your wife undiagnosed Cancer because the doctor was too busy....working on his Tractor!

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jroy

· #10 · Oct 13, 2010

Didn't think of it that way, your right, carry on dictating what he should do with his free time.

DrDave1958

Discussion Starter · #11 · Oct 14, 2010

Well I got the valves adjusted tonight (Special thanks to Walt Conner for the instructions), but it didn't remedy the problem. I can't see any cracks in the intake manifold or gasket, and no obvious defects anywhere.

I've uploaded a video here so you can hear the problem.

Still looking for suggestions.

Thanks,
Dave

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Fcubman

· #12 · Oct 14, 2010

It appears to have a 2-barrel type carb. If it does, I think that the jet on one side is plugged, making it run lean. Putting the choke on enriches the mixture, so it runs better. Running out of gas often stirs up dirt that's lurking about.
I would remove the carb and very carefully look for a plugged jet.

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Kbeitz

· #13 · Oct 14, 2010

A mouse nest will make the valve seat come loose...
Remove the head and look...

DrDave1958

Discussion Starter · #14 · Oct 18, 2010

Fcubman said:
It appears to have a 2-barrel type carb. If it does, I think that the jet on one side is plugged, making it run lean. Putting the choke on enriches the mixture, so it runs better. Running out of gas often stirs up dirt that's lurking about.
I would remove the carb and very carefully look for a plugged jet.

Fcubman you get the ceegar, your diagnoses was spot on. Pulled the carb, then pulled the float bowl and man was it full of junk. Evidently the bowl is rusting in the bottom around the shutoff valve, I should probably get a new bowl. I must say, this is a very interesting carb in that it has absolutely no adjustment screw on it, and it is, in essence a 2 bbl carb. Never seen one like that before. I am also very impressed at how well this engine runs on one cylinder.

Thanks again,
Dave

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Fcubman

· #15 · Oct 18, 2010

Glad to be of some help, and pleased that you found the problem.
Thanks for getting back to us!
Is the bowl made of steel or iron? It would have to be, to be rusting. The rusty looking stuff could be dirt or even (rarely) bacteria. Try a magnet on the "rust" and see if it attracts it. (Rust is magnetic.) You might be seeing fine dirt particles that got pushed through when the empty bowl was filling after being run out of gas. In some areas, dust is magnetic because of the iron content, but that's pretty rare.
I'll try for two - it's not rust, it's dirt.

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GT_80

· #16 · Oct 18, 2010

DrDave1958 said:
I am also very impressed at how well this engine runs on one cylinder.

I plowed my driveway for two hours once with my 18HP Onan, and i thought it was being lethargic and lazy, so I opened the hood, and forgot to reconnect one of the plug wires from the night before when I was looking for the plug number... Again, amazed at how well it ran even slinging the other piston around!! Just shows how great the Onans are (when they run right!!)

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DrDave1958

Discussion Starter · #17 · Oct 18, 2010

Fcubman said:
I'll try for two - it's not rust, it's dirt.

So sorry, you're 1 & 1. the rust IS magnetic. The bowl appears to be a stamped steel bowl that was annodized. I'll probably see if I can get another one or at least put some rust reverser on it.

Thanks again for the help,
Dave

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Fcubman

· #18 · Oct 19, 2010

Oh well, .500 isn't too bad…
Glad to help, and now I have heard of steel carb bowls. I didn't know they existed. Thanks for the reply!

GT_80

· #19 · Oct 19, 2010

Fcubman said:
Oh well, .500 isn't too bad…
Glad to help, and now I have heard of steel carb bowls. I didn't know they existed. Thanks for the reply!

I have a steel bowl on my LME Tecumseh carb on my SS12

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