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Any ideas on why a 12.5 I/C non ohv engine would crank over hard. The engine literally stops on it's compression stroke and I can reach and grab the vented cover to the fan and turn it through the stroke by hand. I hooked a jump box to the starter to eliminate wiring as a cause. took the head off and the valves and piston seem fine. if I remove the spark plug it cranks over repeatedly but slow. I'm thinking starter since i can turn it over by hand and I eliminated wiring any other ideas and any obstructions or stuck valves. If anyone has any ideas other than bad starter I'd surely take a look at them. It ran fine before it was parked a few years ago because of some medical issues. I drained the fuel tank, cleaned the carb, checked the exhaust for obstructions and changed the oil before even trying to start it. then I put a new battery in it only to find out I have this problem.

I have always liked checking voltage, amp draw and voltage drops.

But if you feel that your starter is the problem, take it off and look inside.. the bushings could be worn and dragging, the brushes could be bad, you might have a broken of loose magnet. Quick look inside will show any of these... :smile:KennyV

kellogg49055 said:

Any ideas on why a 12.5 I/C non ohv engine would crank over hard. The engine literally stops on it's compression stroke and I can reach and grab the vented cover to the fan and turn it through the stroke by hand. I hooked a jump box to the starter to eliminate wiring as a cause. took the head off and the valves and piston seem fine. if I remove the spark plug it cranks over repeatedly but slow. I'm thinking starter since i can turn it over by hand and I eliminated wiring any other ideas and any obstructions or stuck valves. If anyone has any ideas other than bad starter I'd surely take a look at them. It ran fine before it was parked a few years ago because of some medical issues. I drained the fuel tank, cleaned the carb, checked the exhaust for obstructions and changed the oil before even trying to start it. then I put a new battery in it only to find out I have this problem.

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adjust the valve they are too loose and the decompressionor wont work set at .004 intake and .005 exh

this isnt the OHV version and the valves are within spec's. I had one that was a little worn so I did some welding and grinding and it's fine now but like I said I can turn it over by hand just by grabbing the metal vent that screws on top the flywheel to protect the fins so it's not a decompression issue. I bought a new head gasket just because I tore it apart to check for obstructions and a new starter. I'm going to put those on today. I also picked up a 14 horse I/C quiet model engine used for 150.00 and if the 12hp doesnt work out atleast the new starter is the same as the one on the 14 too so I'm not wasting my money. I'd just put the 14 on because this originally had a 15 and it got ran out of oil so all I had was the 12.5 which was used for 2 years untill this year but I just have alot going on so if i can use the 12.5 for now I'll put the 14 on when this winter comes and it's not in use.

sounds like you have a starter its easy to swap and try if still the same you need to voltage drop all battery to starter motor connections and battery negative terminal to starter case and engine block while cranking for both circuits.. are you familiar with how to voltage drop test.? you stated you hooked up a jump box to starter but didnt state that it now turns over good or not.

yes, I am very familiar with voltage drop and such. I did a voltage drop and it was fine, but then the solenoid burned out from me trying to crank it too much. I could turn the key and energize the starter relay but the terminals were bad inside that made contact. I could jump the relay and make it crank so I know thats bad. That was one reason I used the jump box and another was to verify my voltage drop test. It did exactly the same with a 1700 cranking amp industrial jump box hooked directly to itl It will turn over slowly but it will complete consecutive revolutions with the plug out. But with the plug it it would do the same. crank slow till it's compression stroke then stop and I could grab the little cover on top of the fly wheel for cooling and keeping out debris and turn it through the compression stroke by hand. I could also take the jump box off and turn it over by hand with no issue's. Even though I knew it was probably a weak starter I took the head off (6.00) part and inspected. Everything was fine, cleaned up the head, piston and valve area and put it back on. I have a new starter to put on it so I'll try that. Now my problem is I took off the carb to clean it and now I cant figure exactly how the linkages go from the carb to the bracket where the cable is along with the governor if anyone has any ideas on that.

@kellog.........hello , what's the conclusion .? I'm having the xact same issue on my Briggs 12.5 .. wont turn all the way over . Stops on the compression stroke . Was running fine . bought new Bat. & Solenoid , also tried the jumper box , still the same , stops on compression stroke , but spins freely with the plug out ....uhg , baffled

What are your valve clearances? The compression release won't work if they are out of spec.

well their isnt that much too it , you said you had the head off, did it have carbon on piston top and or cyl. head , I just had a 2 cyl. 18 hp that cranked hard also and what I did was finally sprayed water mist thru carb while on high idle to clean off piston and combustion chamber. or you might have too much timing advance, which I was told once if you set the coil gap from .030 to about .060 it would retard the timing maybe 2 to 3 degrees. ,, just food for thought. I you voltage dropped and non over 1 volt while cranking and starter is new I think you stated ..that should be it . unless the top of cyl. bore is scored but that you would of seen with head off.. let me know.

woi2ld said:

@kellog.........hello , what's the conclusion .? I'm having the xact same issue on my Briggs 12.5 .. wont turn all the way over . Stops on the compression stroke . Was running fine . bought new Bat. & Solenoid , also tried the jumper box , still the same , stops on compression stroke , but spins freely with the plug out ....uhg , baffled

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clamped my jumper box black/neg. directly to the block (oil fill ) red to the bolt on the starter........turned over fine........conclusion ; deviance in the wiring , ground maybe . But now carb problems filled the crankcase with gas , kelloggs PM'd me how to fix that one . thx bud

You need a different battery. Need more cold cranking amps.

Or starter is going out. Easy to rebuild and fsirly cheap but would start with new battery.

paul8mm said:

well their isnt that much too it , you said you had the head off, did it have carbon on piston top and or cyl. head , I just had a 2 cyl. 18 hp that cranked hard also and what I did was finally sprayed water mist thru carb while on high idle to clean off piston and combustion chamber. or you might have too much timing advance, which I was told once if you set the coil gap from .030 to about .060 it would retard the timing maybe 2 to 3 degrees. ,, just food for thought. I you voltage dropped and non over 1 volt while cranking and starter is new I think you stated ..that should be it . unless the top of cyl. bore is scored but that you would of seen with head off.. let me know.

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I had the same problem with my 18 hr brigs twin cyl . It ended up being battery cables . Installed new cables and i think that the ground was bad to . Works like a new one now.

I just now read through this posting. I don't want to sound insulting, but I didn't notice if you had said anything about checking the oil level or not. Too much oil will cause this same problem. It's a simple thing to overlook, but it happens.