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?
AllisKidD21 Moderator
5000+ Posts
5000+ Posts!
2020 Build-Off Entrant
2020 Build-Off Entrant
1st Place Build-Off 2019
1st Place Build-Off Winner 2019
Age : 25 Join date : 2016-07-10 Points : 8513 Posts : 5190 Location : Ontario Canada
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?
"This'll either wake you up or put you to sleep forever!"- Red Green "Whatever you do you should do right, even if it's something wrong." - Hank Hill
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.
AllisKidD21 Moderator
5000+ Posts
5000+ Posts!
2020 Build-Off Entrant
2020 Build-Off Entrant
1st Place Build-Off 2019
1st Place Build-Off Winner 2019
Age : 25 Join date : 2016-07-10 Points : 8513 Posts : 5190 Location : Ontario Canada
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.
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.
Double W Cross Ranch Veteran Member
2500+ Posts
2500+ Posts!
2018 Build-Off Finalist
2018 Build-Off Finalist
Age : 20 Join date : 2017-06-09 Points : 5418 Posts : 2640 Location : Literally Nowhere, Texas
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.
Double W Cross Ranch Veteran Member
2500+ Posts
2500+ Posts!
2018 Build-Off Finalist
2018 Build-Off Finalist
Age : 20 Join date : 2017-06-09 Points : 5418 Posts : 2640 Location : Literally Nowhere, Texas
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!
JB_4x4 likes this post
RichieRichOverdrive Moderator
2500+ Posts
2500+ Posts!
2018 Build-Off Entrant
2018 Build-Off Entrant
2024 Build-Off Entrant
2024 Build-Off Entrant
Age : 22 Join date : 2016-10-29 Points : 7020 Posts : 3898 Location : Lewisburg, KY
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
AllisKidD21 Moderator
5000+ Posts
5000+ Posts!
2020 Build-Off Entrant
2020 Build-Off Entrant
1st Place Build-Off 2019
1st Place Build-Off Winner 2019
Age : 25 Join date : 2016-07-10 Points : 8513 Posts : 5190 Location : Ontario Canada