12.5 HP B&S Starting Issues.

Hi! I have a B&S 12.5 that has starting issues, and I can't diagnose the issue. I just rebuilt it, valve job, new carb, spark plug, ignition coil, head gasket, and fuel line.
I rebuilt it in an MTD chassis that I didn't like and it started when it was on that chassis.  I moved it to the Craftsman chassis, and it still started, and I waited about a week for the pulley to show up. In that time there was no gas in the carb. I installed the pulley and belt, and then started it, but didn't have time to try to drive it.  The next day, it won't start at all.    It has compression, spark, air, and gas.  It won't even fire when I use starter fluid.
I don't think the ignition key or the timing is off, but I will look into that if ya'll think I should.  I just didn't know what to do, so...any suggestions?

If it won't fire even on starting fluid, and you're sure it has good spark and compression, I'd think that the spark timing was off. Maybe the flywheel key sheared off for some reason. Did you have the flywheel off at any point? If so did you torque the nut down to spec?

I didn't take the flywheel off. I think the plastic cover under the mesh is missing a bolt. Would that make that big of a deal? It's been missing for as long as I've had it and it has started before.

I'm not sure what you mean by plastic cover, you mean the plastic cooling fins under the mesh?

Yeah.

Yeah I dont really think that would be too much of an issue.

AllisKidD21 wrote:

If it won't fire even on starting fluid, and you're sure it has good spark and compression, I'd think that the spark timing  was off. Maybe the flywheel key sheared off for some reason. Did you have the flywheel off at any point? If so did you torque the nut down to spec?

I agree with allis.  Look to see if the flywheel key is sheered or not.

Also, is it a flat head or OHV? You mentioned doing a valve job, if ohv maybe readjusted again, but I'm guessing flat head.

It's a flathead. I'll check the flywheel key; I think I have an extra.

Maybe check the oil to see if there is gas in it. Float bowl might have been leaking into cylinder and flooded it, past the piston and got into the oil.

I checked. Have normal amount of oil however it smells kind of like gas. What would I do to fix it or make sure that's the issue?

Maybe crank it over for a few seconds and then take the plug out to see if it is wet and oily.

Pull the plug to see if it is wet from gas. If the float is leaking, easy fix is a fuel cut off in the gas line from tank to to carburetor. To dry out the plug from gas on it, put a flame to it, from a propane torch, or butane torch, or a lighter, to burn gas off. Crank engine over with spark plug out, to dry out cylinder, crank for about 10 seconds. Then put back together and see if it runs. Spark plug worked before, should work again. If plug is completely dry, then this isn't the problem.

Plug was wet. Went and did all that stuff, and it still didn't start. I tried starting fluid again, and it didn't work. Then I noticed my choke was jammed...so unjammed it and tried it again with fluid, and it momentarily fired. Then I looked at my fuel line and noticed the fuel was off....

I'm so embarrassed. Thanks for your help!

It happens to the best of us man! Sometimes even the experts overthink things and overlook the simplest stuff!

Always the simplest thing. But I like it when it is.

Yeah, could've been worse.

Reminds me of the time I took the simplicity in the pond with the fuel shut off...once the fuel in the bowl ran out she puttered out. I’m in he middle of the pond trying to pull start the thing and then I remembered, oh yeah, fuels off. Started first pull once the fuel was on

Hahaha, stuff happens. Better to be something silly like that than a big problem.