Murray Riding Mower Engine wont turn unless spark plug removed

tbone

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
I have an older 1999 Murray riding lawn mower 14.5 horse Briggs and Stratton IC quiet engine. Over time the mower has gotten harder to crank and have had to use jumper cables to get the engine to turn over fast enough to crank. This is even with a brand new battery. I have replaced the other components (starter solenoid). Interesting enough if I remove the spark plug, the mower engine will turn over freely. I thought it might be a clogged muffler so I removed the muffler. Still wont turn over with spark plug in.

So could this be the starter, even though it appears to still crank? Could it be just a little engine pressure causes the starter to hang? With the spark plug removed, there is little engine pressure.

Any suggestons will be appreciated. A new starter is around $100 so I want to be sure before I go buy one.
 

KennyV

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
Hello tbone.. and Welcome to this often fun Forum...
If the starter is getting full voltage when attempting to start the engine, there should be no difference between starting with a good battery OR starting with a boost from another battery...Check voltage at the starter While it is attempting to start the engine.

Your starter could be dragging, Is the cable at the starter getting HOT while trying to start? Does it get HOTTER when you jump start? If you have an Inductive Ammeter you can measure the actual current...

If it is dragging you may have a cracked magnet, bad brushes, worn out bushings or a short in the armature... :smile:KennyV
 

jeff

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
I agree. But there is one other possibility, the engine likely has a compression release. If it is broken, or if the valve adjustment is too wide the release will not operate properly.
 

BKBrown

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
Exhaust valve not opening ??????? Excess pressure unless plug is removed ????
Compression release sticking would cause excess pressure.
 

Jetblast

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
If the compression release is working, the engine should spin pretty much the same with a spark plug or without. I believe that engine uses the exhaust valve also as a compression release valve, so if your valves aren't adjusted just right, the very small compression release lobe on the cam won't move the valve enough to release pressure for starting. That might be something to check.
 

tbone

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
Hello tbone.. and Welcome to this often fun Forum...
If the starter is getting full voltage when attempting to start the engine, there should be no difference between starting with a good battery OR starting with a boost from another battery...Check voltage at the starter While it is attempting to start the engine.

Your starter could be dragging, Is the cable at the starter getting HOT while trying to start? Does it get HOTTER when you jump start? If you have an Inductive Ammeter you can measure the actual current...

If it is dragging you may have a cracked magnet, bad brushes, worn out bushings or a short in the armature... :smile:KennyV

Yes, the lead wire and starter both get very hot. I have seen the starter actually smoke from time to time. I think I will pull the starter and take to a local repair shop and have them test it. Hopefully that's the issue. i did notice after posting that others have had similar problems some dealing with valve adjustments. Hopefully won't have to go that route.
 

tbone

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
If the compression release is working, the engine should spin pretty much the same with a spark plug or without. I believe that engine uses the exhaust valve also as a compression release valve, so if your valves aren't adjusted just right, the very small compression release lobe on the cam won't move the valve enough to release pressure for starting. That might be something to check.

Thanks Jetblast. I read some other posts stating similar issues with valve adjustments. Here is a link to the exact briggs and stratton user manuals and parts list. Don't know if you can tell by looking at this if what your suggesting is possible or not. It does appear to be a single cylinder engine.

http://www.briggsandstratton.com/engines/support/?NTT=287707-1272-E1
 

glennsjr

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
I would do a compression test. Even though they don't give compression figures should still be able to see if it's high causing the problem. When you jump it are you jumping it to the battery or jumping it directly to starter? sounds like maybe a bad ground.
 

tbone

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
I would do a compression test. Even though they don't give compression figures should still be able to see if it's high causing the problem. When you jump it are you jumping it to the battery or jumping it directly to starter? sounds like maybe a bad ground.

usually jump to battery but have tried to jump directly to starter. Both have the same results. After doing a little more reading, I found some youtube videos showing how to adjust the valves. Looks pretty easy to check so I'll try that as well.
 

Jetblast

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  • / Murray Riding Mower Engine wont turn unless spark plug removed
Thanks Jetblast. I read some other posts stating similar issues with valve adjustments. Here is a link to the exact briggs and stratton user manuals and parts list. Don't know if you can tell by looking at this if what your suggesting is possible or not. It does appear to be a single cylinder engine.

http://www.briggsandstratton.com/engines/support/?NTT=287707-1272-E1

That looks like a likely suspect, especially if you've never adjusted the valves before. From the illustration I see rockers and valve lash adjustability, so I'd go right to that next since they're probably overdue for adjustment anyway. Best case scenario is you do routine maintenance and fix a big problem in one fell swoop.
 
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