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JD D100 Will Not Start

#1

P

PapaDrew88

Hello,

I'm Working on this JD D100 riding mower, 17.5 HP B&S OHV for elderly neighbor. Neighbor was cutting his grass and then it cut off and will not start back. Engine turns over fine. Mower is 10 yrs old and has been serviced annually.
1) Great Spark
2) Getting plenty of fuel (removed hoses and fuel flow is good, new air filter, fuel filter)
3) Removed fuel bowl and everything looks brand new inside bowl, no varnish
4) Removed spark plug and piston is moving in and out
5) Gas spits out plug hole when choke is on trying to crank
6) Oil level is good (mower serviced in Sept)
7) Verified fuel shutoff solenoid is working correctly
8) Did a compression test with and compression is 100psi
9) Shaft is turning all the way to main drive pulley but have not pulled flywheel off to check key

What am I missing? I feel it is something internal. Thanks for any suggestions.


#2

B

bertsmobile1

GEt new pug and a can of carb cleaner .
Give the engine a short shot of carb cleaner down the plug hole, replace the plug & crank the engine
It should fire once or twice
If not then the timing key is broken or a valve is stuck fully open

If so do the same down the carb throat
Should start.
If it does hen continue to give it short shots of carb cleaner for a minute or so.
If you can then the mower definately has a fuel supply problem

Let us know what you find


#3

P

PapaDrew88

Hi, thanks for the response. I sprayed a bunch of starting fluid in the plug hole and tried a new plug and still didn't hit. Sprayed it down the carb throat and also sprayed it into the intake valve. Also I checked the valves and they are moving in and out as they should. Valve clearance is correct. Also removed the flywheel and key looks brand new.
Maybe it is an internal issue and the timing is off?


#4

B

bertsmobile1

Take the blower housing off and note where the magnet is with respect to the magneto coil when the piston is closest to the head.
It should be just past 1 leg of the magneto coil if the cam is in time with the crank .
Also have a close look at the valve stems / rockers .
The valves are the same length so should sit at the same height when the piston is in the firing position .
F you find debris under the blower cover that is obstructing the air flow then a valve guide could have shifted .

ANd when ou said a "bunch" of starter fluid. I hope you meant a very SHORT SHOT like about 1/2 second because you can flood an engine just as easy with stater fluid as you can with pouring fuel down the plug hole or holding the choke on .


#5

P

PapaDrew88

Thanks again, Ill take a look at these suggestions, yes it was several short bursts of starting fluid but I done it several times throughout the troubleshooting process.


#6

B

bertsmobile1

If the valves are not working but the pug is firing at te right time then you should have gotten some sort of fire with starting fluid down the plug hole
Through the carb if the inlet is not closing\Through the exhaust if the exhaust is not closing
A single muffled fire then backwards if neither valve is opening .


#7

P

PapaDrew88

Hi Mr. Bertsmobile1,

I finally had an opportunity to look at the next steps of the troubleshooting process per your tips. I am enclosing some pics my findings. When the piston is closest to the head, the valves appear to be sitting at the same height. The magnet I assume is in the correct position in relation to the magneto. Also when I pulled the valve cover off, the oil seems to have a strong fuel smell, but not sure if that is normal since it is in the valves. I also bought a compression gauge and I have a compression of 100psi. I was going to send you a video of the mower turning over and the spark I'm getting but I am unable to upload it. I look forward to hearing your response Sir, thank you!

Attachments







#8

B

bertsmobile1

Take the valve photo from the other side
You are looking for the position of the end of the valve but laying the square on the edge of the springs, it should be parallel to the gasket face if the valves are at the same height.
oil that smells like fuel is caused by the float valve not stopping the flow of fuel into the carb.
The float bowl has an air vent in it which because of EPA regualtions is now internal so you can not see the fuel leaking.
IT dibbles out of the carb then trickled down the manifold into the engine then past the rings and into the sump.
IT must be removed before you try to start the engine
and of course the carb needs to be fixed .


#9

P

PapaDrew88

Thanks, I will check it out and take pic as soon as possible. This really means a lot, you are a great teacher.


#10

P

PapaDrew88

Hi Mr. Bert,
Here is a pic of the valves from the other side as you suggested. They look to be the same height. I have also left a picture of the carb in full choke position and throttle position at low speed.
I took the carb apart and checked everything. Carb looks brand new. There is no sediment or varnish build up.
The float is working properly and sealing off. No flow when fully seated. I blew out the orfices with a small air pressure and reassembled.

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#11

Scrubcadet10

Scrubcadet10

put the carb in full choke position, and then with your finger push the top right corner of the choke valve in, see if there is any play inwards.


#12

Scrubcadet10

Scrubcadet10

BTW, did you ever check the flywheel key


#13

B

bertsmobile1

Did you get any sort of ignition with using very SMALL shots of starting fluid down the plug hole and a fresh plug ?
Till that happens then you are just chasing shadows.
What we seem to have missed is the timing key in the flywheel.
Undo the flywheel bolt and check the key ways
The 2 halves should joint together to make a perfect square & I mean perfect square.
That magnet looks a little too far past the magneto coil for the piston to be at TDC


#14

P

PapaDrew88

Good morning all,

Still no ignition with small bursts of starting fluid.
I checked the flywheel key way last week. I pulled it off and it looked brand new, no evidence of sheering.
I will check TDC.


#15

Scrubcadet10

Scrubcadet10

Have you Checked for spark with the coil kill wire unplugged?


#16

P

PapaDrew88

no play inwards on the choke valve
no spark with the coil kill wire unplugged, plenty of spark when plugged in to coil
This is the position of the flywheel at the ignition coil at TDC
1605805204495.png


#17

B

bertsmobile1

Now I am really confused
Are you saying when you pull the black wire with the white plug that is just under the left side of the coil off you get no spark and when it is re-connected you get a good spark ?
It should be the other way round, or a good spark both ways if the safety switches are all working as they should .
Please check that black wire
It should be closed to ground with the key in the off position & open with the key turned on .
Also check it for voltage there should be none in any key position .
So as I see it ( and there are a lot of things I have never seen ) the mower has a faulty coil


#18

P

PapaDrew88

Interesting, I will check and verify tomorrow


#19

P

PapaDrew88

Just letting you know where I am with this. I believe it is a carb problem and flooding. I ordered a new carb for $20 and going to give it a shot. When i pulled the plug out fuel ran out of the plug. I drained the oil and pulled the filter off and it had smelled like gas.


#20

Scrubcadet10

Scrubcadet10

if it dumped that much fuel, the needle failed in the carb. It limits the amount of fuel allowed into the bowl, since the float is attached to it.


#21

P

PapaDrew88

So I did an oil and filter change, installed a new spark plug and then I installed my new Nikki carb and heard a few misfires (a small popping) and then a big backfire pop, big plume of white smoke came out the muffler. Still turns over fine but the temp is in the mid 30s so it doesn't take long for the battery to run down.
I assume the Nikki is plug and play? I didn't make any adjustments.


#22

P

PapaDrew88

Just finished pulling the head off, cylinder was full of gas. Seems like it is still flooding with the new carb. Cylinder, piston, head, valve springs all look good and valves are seating properly.
I will adjust the valves tomorrow and finish putting it back together. I'll post pics of the piston at TDC and the magnet on the flywheel after dinner.


#23

P

PapaDrew88

Here are the pics of the piston and magnet is at TDC and valve springs. The carbon build up looked normal, I cleaned it up a little. The cylinder had no wear.
For some reason I still think it is flooding with the new carb. The cylinder was full of gas as I stated earlier.
Could it be a timing issue and gas is building up in the head and therefore the reason it is not firing?
How do you check timing?
It was a free lawn mower so I'm not giving up. Thanks!

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#24

Scrubcadet10

Scrubcadet10

Small engines are timed two ways.
The flywheel key aligns the flywheel to the crank for proper ignition timing, and then the Cam shaft and crank gears have a dot that must be aligned for proper valve timing


#25

P

PapaDrew88

So a little progress, I changed the ignition coil and now it is backfiring like crazy, still not running. Any suggestions?


#26

P

PapaDrew88

Small engines are timed two ways.
The flywheel key aligns the flywheel to the crank for proper ignition timing, and then the Cam shaft and crank gears have a dot that must be aligned for proper valve timing
I replaced the magneto coil and now it is backfiring. Still want crank.


#27

Scrubcadet10

Scrubcadet10

i would check the flywheel key next. you may need to remove the flywheel nut/bolt to see it.
also i read that this JD uses the 31 series Intek, which has had camshaft problems, i remember one where the exhaust lobe was worn down and causing it to backfire and pop.


#28

P

PapaDrew88

i would check the flywheel key next. you may need to remove the flywheel nut/bolt to see it.
also i read that this JD uses the 31 series Intek, which has had camshaft problems, i remember one where the exhaust lobe was worn down and causing it to backfire and pop.
Ok I will check the flywheel key again thanks


#29

P

PapaDrew88

Ok I will check the flywheel key again thanks
Mfg. No: 31G777-0171-G5 is the engine number.
Checked key way and it looks brand new
I forgot to mention this earlier. So after I changed the magneto coil, the mower fired up and started running for a few seconds and then blew the main fuse. The reason it blew the fuse is because I had blown the 20 amp when I first started working on the mower and replaced it with a 5 amp just so that it would fire ( I didn't have a 20amp replacement).
I took the 20 amp from my other JD LA140 and installed it in the other mower. Once I did that and tried to crank, that is when it started backfiring while it was trying to crank.


#30

P

PapaDrew88

I decided to get back on my mower project. It is now sheering the flywheel key once it starts up and runs a few seconds. I'm convinced something is broke internal.


#31

Scrubcadet10

Scrubcadet10

What are you torquing the flywheel nut to?


#32

1

100 td

I note some things I would do, but from a safety aspect, you should refrain from the following and allow a professional to do your repairs. From your first post, it appears everything was basically good, except that the mower stopped, get back to original and check one thing at a time.It appears that some basic checks may not have happened before tearing down and changing things. No worries, I would just try to get back to original and check one thing at a time.

As previously noted, there is a possibility that the flywheel has been incorrectly installed or torqued incorrectly and has slipped/sheared. A backfire can shear a key at any time, especially if it wasn't replaced or torqued correctly. Clean/fine sand paper the flywheel and shaft with 1000~2000 wet/dry.
Remove key, install flywheel without key, make sure it is set down evenly and doesn't wobble, do up flywheel nut, torque to spec 100 lb-ft (use a tension wrench), measure the length of the thread protruding past the nut with a vernier, also mark/scribe a line from the nut to the flywheel, undo, remove flywheel, place key in-situ, replace flywheel/key, ensure even and no wobble, tension nut and check with vernier that it is the same, and check scribe mark. Many times a key may hold up the flywheel by a tiny amount, it is the mating surfaces of the taper that do the holding, not the key, the key is only a locating/alignment device, and it's generally made of aluminum so that it shears if the forces on the mating surfaces are too great, and can be easily replaced without damage to shaft or flywheel.

Put the ORIGINAL ignition coil back on and set air gap 10 to 14 thousandths of an inch. (use feeler gauges)

Carefully check all wiring for any rub through that may blow the fuse (entire mower wiring harness)

Turn off any ancillaries on the mower, headlights, blade clutches etc.

Slow charge the battery overnight so it is fully charged before you start any investigations again.

Check oil level, if it is over full, completely drain oil and replace with new oil to correct level. If it is low, either top up, or drain /replace to correct level.

If your model has the fuel tank above the carby and uses gravity flow, remove bowl and turn fuel on and ensure good flow, then carefully use a pencil or other apparatus to lightly lift the float to ensure easy fuel shut off. If fuel is low and uses a fuel pump, run a fuel hose from a small bottle above to do the same test. If fuel shut off is not accomplished with very light pressure on float at approx horizontal position, replace needle.
As you have stated you have a fuel flooding issue, ensure the previous step is carried out thoroughly. Also, if you have a crankcase/differential/electric pressure driven fuel pump, disconnect the fuel supply going to it, and from it and rig up a gravity feed fuel supply to the carby for testing/running until engine running is sorted. This gets rid of fuel pressure and also possible fuel leakage past the diaphragm into the crankcase or intake or where-ever this pump is plumbed to.

Ensure no flammables in work area. Ensure no fuel, liquid or vapor leaks in general area. All testing to be done in a wide open outside area with approiate safety/fire extinguishers etc.. First engine test, no air cleaner, fuel tap off if it has one, gravity fed fuel, remove spark plug, plug spark plug into high tension lead and ground the plug well away from the plug hole, well away from the carby, open throttle wide, but not so that choke flap closes, crank engine and check for spark, crank for 10 SECONDS and check that spark stops when key is turned off and engine is still spinning.
Replace spark plug into plug hole, tension to 180 lb-in.
Plug high tension lead onto spark plug. Turn on fuel, allow 30 seconds, manually engage choke or ensure choke lever has engaged at full throttle, crank engine for 5 seconds, or less if it fires. If it doesn't fire, dis-engage choke, full throttle or close to full throttle so choke does not close, crank for 5 seconds. Report your findings back here, someone will make a comment. If you have no success, listen to advice/checks here, but only check/test one thing at a time.

The 31 series engine also have a big problem blowing head gaskets across to the pushrod gallery. They can blow through the middle layers of the gasket, gasket in place. Zooming in on your image, there is a small section that may be damaged. Aftermarket solid copper gaskets are available for these engines. Check this is the correct one if you wish to follow it up and I'm sure there are other suppliers of different gaskets.
I won't go into checking head/cylinder for flatness here. Don't forget to tension head to 220 lb-in in correct sequence . Do not torque each screw in one step as it may result in a warped cylinder head. Step-torque all screws to approximately 1/3 of final torque value, then to 2/3 final torque value, then finish at final torque value.
When 4 bolts are on left side, from top to bottom, 5, 8, 6, 3, then middle two, top is 2, bottom, 1, then two on right, top is 4, bottom is 7.

If you are in any way hesitant or don't have the skills to do any of the above safely, especially with regards to fuel (liquid and vapor), ignition sources from spark plugs or shorted wires, please leave it to the professionals. These are my thoughts only, others on this forum, professional or otherwise may have different views, that's fine, go with them in preference to me. I believe the torque specifications and patterns are correct for your engine, but you need to check that they are. Actually, take all the above with a grain of salt.


#33

P

PapaDrew88

What are you torquing the flywheel nut to

What are you torquing the flywheel nut to?
Just tightening it up by hand with my 1/2" drive ratchet


#34

P

PapaDrew88

I note some things I would do, but from a safety aspect, you should refrain from the following and allow a professional to do your repairs. From your first post, it appears everything was basically good, except that the mower stopped, get back to original and check one thing at a time.It appears that some basic checks may not have happened before tearing down and changing things. No worries, I would just try to get back to original and check one thing at a time.

As previously noted, there is a possibility that the flywheel has been incorrectly installed or torqued incorrectly and has slipped/sheared. A backfire can shear a key at any time, especially if it wasn't replaced or torqued correctly. Clean/fine sand paper the flywheel and shaft with 1000~2000 wet/dry.
Remove key, install flywheel without key, make sure it is set down evenly and doesn't wobble, do up flywheel nut, torque to spec 100 lb-ft (use a tension wrench), measure the length of the thread protruding past the nut with a vernier, also mark/scribe a line from the nut to the flywheel, undo, remove flywheel, place key in-situ, replace flywheel/key, ensure even and no wobble, tension nut and check with vernier that it is the same, and check scribe mark. Many times a key may hold up the flywheel by a tiny amount, it is the mating surfaces of the taper that do the holding, not the key, the key is only a locating/alignment device, and it's generally made of aluminum so that it shears if the forces on the mating surfaces are too great, and can be easily replaced without damage to shaft or flywheel.

Put the ORIGINAL ignition coil back on and set air gap 10 to 14 thousandths of an inch. (use feeler gauges)

Carefully check all wiring for any rub through that may blow the fuse (entire mower wiring harness)

Turn off any ancillaries on the mower, headlights, blade clutches etc.

Slow charge the battery overnight so it is fully charged before you start any investigations again.

Check oil level, if it is over full, completely drain oil and replace with new oil to correct level. If it is low, either top up, or drain /replace to correct level.

If your model has the fuel tank above the carby and uses gravity flow, remove bowl and turn fuel on and ensure good flow, then carefully use a pencil or other apparatus to lightly lift the float to ensure easy fuel shut off. If fuel is low and uses a fuel pump, run a fuel hose from a small bottle above to do the same test. If fuel shut off is not accomplished with very light pressure on float at approx horizontal position, replace needle.
As you have stated you have a fuel flooding issue, ensure the previous step is carried out thoroughly. Also, if you have a crankcase/differential/electric pressure driven fuel pump, disconnect the fuel supply going to it, and from it and rig up a gravity feed fuel supply to the carby for testing/running until engine running is sorted. This gets rid of fuel pressure and also possible fuel leakage past the diaphragm into the crankcase or intake or where-ever this pump is plumbed to.

Ensure no flammables in work area. Ensure no fuel, liquid or vapor leaks in general area. All testing to be done in a wide open outside area with approiate safety/fire extinguishers etc.. First engine test, no air cleaner, fuel tap off if it has one, gravity fed fuel, remove spark plug, plug spark plug into high tension lead and ground the plug well away from the plug hole, well away from the carby, open throttle wide, but not so that choke flap closes, crank engine and check for spark, crank for 10 SECONDS and check that spark stops when key is turned off and engine is still spinning.
Replace spark plug into plug hole, tension to 180 lb-in.
Plug high tension lead onto spark plug. Turn on fuel, allow 30 seconds, manually engage choke or ensure choke lever has engaged at full throttle, crank engine for 5 seconds, or less if it fires. If it doesn't fire, dis-engage choke, full throttle or close to full throttle so choke does not close, crank for 5 seconds. Report your findings back here, someone will make a comment. If you have no success, listen to advice/checks here, but only check/test one thing at a time.

The 31 series engine also have a big problem blowing head gaskets across to the pushrod gallery. They can blow through the middle layers of the gasket, gasket in place. Zooming in on your image, there is a small section that may be damaged. Aftermarket solid copper gaskets are available for these engines. Check this is the correct one if you wish to follow it up and I'm sure there are other suppliers of different gaskets.
I won't go into checking head/cylinder for flatness here. Don't forget to tension head to 220 lb-in in correct sequence . Do not torque each screw in one step as it may result in a warped cylinder head. Step-torque all screws to approximately 1/3 of final torque value, then to 2/3 final torque value, then finish at final torque value.
When 4 bolts are on left side, from top to bottom, 5, 8, 6, 3, then middle two, top is 2, bottom, 1, then two on right, top is 4, bottom is 7.

If you are in any way hesitant or don't have the skills to do any of the above safely, especially with regards to fuel (liquid and vapor), ignition sources from spark plugs or shorted wires, please leave it to the professionals. These are my thoughts only, others on this forum, professional or otherwise may have different views, that's fine, go with them in preference to me. I believe the torque specifications and patterns are correct for your engine, but you need to check that they are. Actually, take all the above with a grain of salt.
Thank you for this detailed explanation, everyone has been so generous with troubleshooting tips. I've learned so much. The broke mower was given to me so I'm determined to fix it on my own. I will get back to troubleshooting using these tips once the weather clears up a bit.


#35

Scrubcadet10

Scrubcadet10

31 series has a 100 Ft Lb flywheel nut torque
1614371646514.png
Give us the complete model number off of the Valve cover and i can make sure the spec is correct.


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