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Curtis B.
Curtis B., Technician
Category: Agriculture and Farm Equipment
Satisfied Customers: 27787
Experience:  Technican turned service manager on multiple lines of equipment and rental equipment.
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I have a Deere self propelled mower, js40 model, my question

Customer Question

I have a John Deere self propelled mower, js40 model, my question is, it does not start. It has spark, and the carb has fuel. (New carb and plug and fuel) it does not fire. Can you help?
Submitted: 10 months ago.
Category: Agriculture and Farm Equipment
Expert:  Curtis B. replied 10 months ago.

If you put fuel direct into the cylinder through the spark plug hole, does it fire for a few seconds? I fnot, time to check the compression, and the timing. If compression is great enough to move a finger held over the spark plug hole, it is ok. Has mower hit any objects that would have stopped engine and sheared the timing key between flywheel and the crankshaft?

Customer: replied 10 months ago.
It has compression, and not sure if it has ever hit anything because I purchased it used.
Expert:  Curtis B. replied 10 months ago.

I would remove the flywheel and check the key. If sheared, it throws off the timing, and will never start.

Customer: replied 10 months ago.
Ok, will try that. Will it still spark if the timing is off?
Customer: replied 10 months ago.
Ok then, will check the flywheel. If is sheared, do you think the mower is still good?
Expert:  Curtis B. replied 10 months ago.

Yes, a sheared key will not damage anything. As long as the crankshaft was not hit and bent!

Customer: replied 10 months ago.
I checked the flywheel, it looks as if it is lined up correctly
Expert:  Curtis B. replied 10 months ago.

Can you see the groove in the flywheel and the crankshaft? And are they perfectly aligned?

Customer: replied 10 months ago.
key is there also. Should I remove the flywheel to be sure? And I don't have a puller, would a gentle tap on shaft pop it off?
Expert:  Curtis B. replied 10 months ago.

At this point I would remove it, any damage at all and it throws off the timing. I would find a small puller, so as not to damage the crankshaft or flywheel.

Customer: replied 10 months ago.
Ok thank you
Expert:  Curtis B. replied 10 months ago.

The only other timing is the crankshaft and cam shaft gear. One other quick check would be to check the valves, you can have compression and the valves may not be opening, say a pushrod is off.

Expert:  Curtis B. replied 10 months ago.

i fact if you are still there, check the valves before removing the flywheel!

Customer: replied 10 months ago.
I pulled it off, and placed it back on exactly lined up. Still no start
Expert:  Curtis B. replied 10 months ago.

did you check the valves?

Customer: replied 10 months ago.
I will check them
Customer: replied 10 months ago.
One of them is off, how do I adjust it?
Expert:  Curtis B. replied 10 months ago.

The rocker arm center nut, has allen head lock screw, loosen it and then turn the outer nut to adjust. # 14 in the link above. .004 to .006 inch.

Customer: replied 10 months ago.
The one rod pushes all the way in, is it suppose to do that?
Expert:  Curtis B. replied 10 months ago.

no, pushrod has to be tight on the lifter on camshaft. You may have something going on with the camshaft. Lobe may be loose!

Customer: replied 10 months ago.
How do I check that?
Expert:  Curtis B. replied 10 months ago.

I fit were mine I would remove the cylinder head and see if I could see the camshaft and lifter, looking for damage. Or remove the engine and remove the sump so you can get to the camshaft to see what has happened.

Expert:  Curtis B. replied 10 months ago.

I see question is still open . did you find problem? Please use 5 star rating to close and get me credit.