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B&S engine struggles when warm


zero_gravity's Avatar
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11-14-07, 09:43 AM   #1  
B&S engine struggles when warm

hello everyone, my first post here.

a lot of this info is second hand as i do not live at home with my mom anymore, and its her lawn tractor thats acting up. i've been learning a lot about car repair but havnt touched a small engine much.

the engine is a B&S model #281707 12 hp. what seems to happen is it will run fine when cold but when it warms up the engine will begin to struggle and run worse and worse to the point where it will barely make it back to the garage.

the spark plug is ok and intake seems clean enough. the air filter is still good and i also did a compression test - that was about 25 psi so i started laughing my ass off.

i've also been told that it could be the spark igniter. putting oil in the cylinder didn't change the c.test and it doesn't seem to be burning oil so that problem points to either valves or the head gasket.

so what i'm hoping to find is where do i start with this? i'd like to rule out the igniter before i do anything else, how would i test that? maybe warm it up with a heatgun and see if thats causing problems? any other ideas?

also and maybe most importantly, where can i get drawings, repair info and torque specs for this engine? any flatness specs for the head/block if i end up replacing the head gasket? i know almost nothing about this engine other than its old haha.

thanks for the help!

 
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GlenM's Avatar
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11-14-07, 09:55 AM   #2  
I had a neighbor lady this happened to once, turned out she was pulling choke out to start, but failed to push it back in after warmed up. Probably not the case here. Might check the choke tho.
thanks,

 
zero_gravity's Avatar
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11-14-07, 12:22 PM   #3  
not the choke...wish it was that simple. i've used this mower myself even. it doesn't happen until its had maybe 20 mins to warm up.

anythings worth a shot though, thanks

 
GlenM's Avatar
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11-14-07, 12:39 PM   #4  
Gas cap not venting properly may be a cause, won't take 20 minutes if completely plugged. When it starts to falter, loosen gas cap. Loosen, or remove nut holding carb bowl on, this will drain whatever is in carb. reinstall nut.

 
Fisher40037's Avatar
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11-14-07, 04:21 PM   #5  
Compression readings on most small engines are useless
so do not go by them much.

Your problem is likely valve related, over time and overheating, the block warps away at the valve area,
making the valve and tappet clearances closer, and also cocking the valve seats so that the valves don't seal
properly. But the clearance is likely your main problem.
As the valve expands, it gets longer when hot/warm,
and no longer fully closes, so adjusting the valve clearances
would probably get you going again, but is not a good
permanent fix, but a good permanent fix is likely more
than you wish to invest. Adjusting the valve clearances involves removing the valves, and grinding the stems, which
would require valve tools, feeler gauges, removing the head and carb, etc. and if you go that far, you might as well
do a proper valve job, which would involve recutting the seats and valves, which very few shops do.
But I digress, your problem is likely valve related

 
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11-14-07, 06:28 PM   #6  
"Compression readings on most small engines are useless
so do not go by them much."....but, I say, if your compression tester is indeed acurate then 25 is waaaayyy low. You definitely should remove the cylinder head and have a look. If you post back with the rest of the engine ID numbers I can help you further...with part numbers, torque specs, etc. Check briggsandstratton.com for useful information.

 
zero_gravity's Avatar
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11-15-07, 06:35 AM   #7  
thanks for the help guys! others are telling me valve problems as well, but its fixable for me by far. might be a good winter job. the compression tester should be fairly accurate, same one i used on my car.

so i hope its not a big job to pull the engine lol

 
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