JD L120 garden tractorl Battery/starter issues 21HP Vtwin

fastline

Member
I do a lot of wrenching and electrical work but I am a little stumped here. This is a Deere L120 with 21HP twin Briggs. Battery is testing perfect and so is the starter, yet 50% of the time, when you bump the key, the engine stalls at compression and will not turn over. Once cranking, it will crank perfect and fast.

Armature test shows 1.0 ohms on every contact. No found issues with brushes, commutator, bearings, etc.

Bat should be rated about a 340CCA. Current/voltage test shows at the stalled condition, 300A to starter, 9.5VDC. A batt should provide 1/2 of CCA at 9.5V so that bat is certainly doing what is was advertised to do.

OEM actually specs a lesser CCA bat. I am inclined to throw MORE CCA at it to keep the voltage higher and get more power to the starter.


What the hell am I missing here? Why is a mower with ""65hrs" having this problem?
 
I would adjust the valves and see if that corrects
the issue.If i remember correctly its .004 on both
intake and exhaust.But it has to be slightly over
TDC.I'm sure others can elaborate more on the
procedure.
 
I thought these had hydro lifters? Regardless, 65hrs? I guess maybe. However, valves usually tighten, causing loss of comp. It is evident I gots plenty of pop in this engine.

I am cranking with the plug wires off to verify no timing issues. I can also manually turn the crank past compression a bit and it will crank, no problem.
 
If after checking/setting valve clearances and you still have a problem check out carb,you may have a sticking/leaking float valve in carb caused by dirt/gum & eng flooding when at rest,causeing piston(s)to hydrolock on inital compression stroke till excess gas blown out cyl(s)this is a somewhat common problem on many smaller ohv briggs eng.Smell oil on dipstick,if you smell gas in oil or have an overfull level then float valve leaking.

If tractor has a shutoff valve between tank/carb try closeing valve after each use,if no valve,add an inline valve & close after each use to see if that cures problem,might also try adding seafoam gas treatment to each tank of gas/gas container & run several tanks of gas thru eng to see if that helps/cures problem before removing/disassembling carb for inspection/cleaning
 

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