Have a 13hp single flathead b&s mower that has starting issues. Tried to jump start it today using car battery and turns over nice with spark plug removed but when the plug is installed it cranks over slowly. Figured out it is the 'power' stroke its having trouble with. A vacuum is being created in the absence of combustion and appears to be too much for the starter and it can't 'pull' the piston back?
bigfatmat1,
Jun 1, 1:00pm
Worn out starter bad connection maybe
intrade,
Jun 1, 1:07pm
no a vaccume can only be 1 bar total as maximum possible. so you can rule that out for sure quote A vacuum is being created in the absence of combustion and appears to be too much for the starter and it can't 'pull' the piston back? end quote a compression stroke will guaranteed be more the 1 bar
intrade,
Jun 1, 1:13pm
its more like one or more valves dont actuarly open causing you symptoms you discribe
bikernutrr,
Jun 1, 3:11pm
Yes thanks :) . Stripped everything down, cleaned carb, checked valve clearance, pulled starter apart( in good nick, all brushes new), wiring good, new plug, took head off and cleaned. Spins brilliantly without plug but as soon as I screw it back in the motor spins 3/4 easily but appeared to 'struggle' to get past 1/4. Turns fairly easy by hand with obvious resistance during 3 strokes but then became very tough to turn. I assume that was where the problem was so took head off and noted that the piston is moving inwards on the 'power' stroke. At that stage the valves are both closed and the starter struggles to turn.
skin1235,
Jun 1, 3:18pm
check the compression, sounds like that starter is the problem , even if it looks all good, standard compression would be about 120-140, and the starter should handle that with ease
bikernutrr,
Jun 1, 4:15pm
Damn, don't want to have to replace starter. Will have to purchase a compression tester and try. Thanks.
aredwood,
Jun 1, 4:44pm
Open up the starter and check brushes. Often they are wired - starter solenoid > through 2 fixed in place coils (stator coils) > through 2 brushes to armature > another 2 brushes to ground. If 1 of those brushes wears out or jams in it's holder meaning it won't make contact. Starter motor will have massively reduced output. Check that the varnish on the stator coils in not blackened (overheated) as it may have shorts to ground or shorts between the turns of wire. (not enough magnetic field). If 1 coil is burnt and the other OK then you have had a brush fail and then take 1 of the stator coils out as well.
skin1235,
Jun 1, 4:48pm
take it as a complete motor to a workshop and ask them to check the compression, will maybe cost $10, cheaper than buying a tester yourself
alfred011,
Jun 1, 9:19pm
The auto compression release on the camshaft has probably flown apart,it allows compression to be released when cranking ,try jump starting with a bigger battery,
bikernutrr,
Jun 1, 9:32pm
That works. but does that mean I have to jump it every time?
skin1235,
Jun 2, 12:33am
in the other thread the compression release was discussed, appears it is quite a simple thing to repair, also how to check if it is working
using a bigger battery all the time will strain the starter and the starter gears and could promote early demise of them
areffer,
Jun 2, 4:10am
Have just gone through the exact same thing with the motor on my ride on. I was convinced it was a starter motor issue but turns out it was valve clearances, the compression release on my motor operates the inlet valve, I set the clearance to 0.003", it was about 0.009" and the mower turns over on starter motor and runs fine now. Clearance needed to be set with piston 1/4" past TDC.
strobo,
Aug 14, 9:00pm
piston rod around the wrong way maybe ? some are off set
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