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Currently attempting to resurrect a free early 90s MTD lawn tractor (wizard brand) that doesn't want to start. Was parked several years ago by the previous owner, carburetor issues were assumed so that was removed to be fixed, the fix never happened, so the tractor was stored outside for at least a year with no carburetor. More issues are being discovered as i dig further into it.

Engine is a Briggs 422707-1512.
First, carb, fuel filter and fuel line were replaced with new. Fresh gas and oil were used. Air filter is removed for testing purposes.
Battery is completely dead, so this was jumped to my car battery with the car running. battery measured over 12v and the starter was drawing 110-140a. i'll have to check voltage under load at the starter, but there was enough juice available to the system to work.
Engine would not start, acting like low battery. Engine wasn't getting enough RPM, doing the whole cha-chung cha-chung sound, slowing rapidly during the compression cycles.
Checked plugs, they were pretty fouled so opened the heads and cleaned the carbon out. Not good, but not the worst I've seen. Attempt again, still not getting enough speed.
Removing either one of the plugs would get the engine up to starting speed.

Therefore I have to assume either the starter motor is weak or i have a valve train issue causing too much compression. The motor is old and doesn't have a automatic decompressor for starting that i can tell based on part diagrams. Its a flat head engine, so there isn't much adjustment in the valve system that i can tell. Neither of the previous owners would be the type of people to go messing that deep into the engine either.

Looking for testing methods to determine if either the starter is bad or its a valve issue. This project is racking up enough bad parts (needs new front tires, battery, air filter, plus whatever is causing the current issue, and haven't gone through the ignition system or the transmission, which is under suspicion) that i am determining if this an economically feasible project. no point in throwing 300 bucks on a tractor only worth 300.

How did you measure starter draw ?
The value is 110-140 amps by your testing. What was the voltage when you did this ?
Amps go up, voltage goes down on a draw test.
Can't find a spec for it but it sounds high for a lawnmower engine.

clamp on multimeter to the positive line going out of the starter, between the motor and the solenoid. Unfortunately I didn't grab a voltage measurement under load, I plan on checking that tonight.

i suppose a bad solenoid connection could cause enough voltage drop to the motor to cause this as well.

Cwalster said:

clamp on multimeter to the positive line going out of the starter, between the motor and the solenoid. Unfortunately I didn't grab a voltage measurement under load, I plan on checking that tonight.

i suppose a bad solenoid connection could cause enough voltage drop to the motor to cause this as well.

Click to expand...

Are you saying you used a tool like this ?

Yes.

bear in mind too that this motor was just barely getting the engine to turn over, so it'd be very nearly stall current.

Do a starter draw test at the starter.
By pass all the rest in the system.

I am no expert on B &S engines but very few of them have no decompression at all.
Older engines had a funny cam grind & decompressed out of the exhaust .
Start by jumping directly to the starter both with a ground & power cable.
Been sitting out in the open could have internally rotted cables or just corroded fixing points.
Make sure the valve lash is in spec and towards the tight end.
Can also be crud in the bottom of the starter
Pulled one apart that was full of ants.

Well that engine has an easy start cam grind on the Intake valve cam lobes for compression release. Often the starter on these wear the top bushing out, oblong, letting the armature drag on the field. I re-bush the end plate/mounting plate when this happens. As said above, check using a good set of jumper cables from a known good battery to the starter first. IF starter spins fast now you know you have a battery, battery cable, switch or solenoid problem. I would make sure the ground cable where it attaches to the frame is bright and clean as well as mounting surface. Also good connection between engine and frame. Let us know your findings.
Walt Conner

Went to monkey with it, started by clamping the ground to the motor and tapping the starter with the jumper. Not the fastest I've seen an engine spin, but enough to get good spark to the plugs. Resistance between battery and solenoid was basically nothing, same between solenoid to starter and engine to battery, so I'd have to assume bad solenoid. Going to dig out a part number and get that ordered, see what else is busted.
Was too late at night to attempt to fire it for real. Gotta wait till tomorrow to check for other issues.

Resistance reading on battery cables are meaningless.
That is why I went to the effort to ask you to use jumper leads
More than once I have found a battery cable that was in several pieces
Just 1 strand of wire .00000000000000000000000000000000000000000000000000000000000001" diameter will give a 0 resistance reading but it won't carry 100 Amps .
We really can not help you if you refuse to do what is asked
Connect the + on the starter to the + on the battery ( best done that way )
Then repeat but add a - jumper from the battery to the starter ( I use the drain plug ) before touching the + to the battery.