17 HP Briggs valve problems

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ekywildcat

Member
Hello all. First time poster. I've worked on car engines all my life, rebuilt CAT, Cummins and Macks engines, but a 17 HP Briggs has kicked my rear end. The model # is 310707. It's on a LT1000 Craftsman mower. Replaced the head gasket and for some reason, I cannot get the valves adjusted to where it will run. Blows back through the carb, it was doing this before I replaced the head gasket also, but it would run some.

I'll get the piston .25" past TDC, set the valves, blows back and won't run. Turn it another turn, set the valves again, same. And when I turn back to TDC the valves are way wide around.125". I tried the method of getting the ex. open and adj the int. then adj the ex. with the int. open, wouldn't run. I've read about the comp. release device, could this be screwed up? The valves just don't seem to working like they should. I'm at my wits end, HELP! :confused2:
 
Did you check when you had the head off that the valves was sealing (fully closed) lamp oil around the seat of the valves will tell you, also did you lap them, and are you sure the push rods are back in the right way ie Rod–Push (Intake) Rod–Push (Exhaust.
 
EngineMan said:
Did you check when you had the head off that the valves was sealing (fully closed) lamp oil around the seat of the valves will tell you, also did you lap them, and are you sure the push rods are back in the right way ie Rod–Push (Intake) Rod–Push (Exhaust.
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Yes I checked the valves. I filled the chamber with gasoline and it didn't leak. And I didn't lap them since they were sealing good. And I have the aluminum push rod on the bottom and steel on top. Thanks for the reply. I'm really stumped.
 
If it "Blows back through the carb" the inlet valve is still open, have you check out the fly wheel key. (timing) and yes you could have a bad release device which is keeping the valve open.
 
If the valves are loose after you set them, You may not be far enough past TDC. You state .25". Try 1/4 turn of the flywheel past TDC.
Backfiring through the carb is timing, flywheel key or the intake valve is not seating.
 
EngineMan said:
If it "Blows back through the carb" the inlet valve is still open, have you check out the fly wheel key. (timing) and yes you could have a bad release device which is keeping the valve open.
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Fly wheel key was fine. So the compression release does work on the intake valve? From my research I wasn't sure.
 
stretch5881 said:
If the valves are loose after you set them, You may not be far enough past TDC. You state .25". Try 1/4 turn of the flywheel past TDC.
Backfiring through the carb is timing, flywheel key or the intake valve is not seating.
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Ok thanks. I'll try the 1/4 turn tomorrow. I think it's in the valves. Key was fine and it doesn't really backfire, it just blows, I can stuff a paper towel in the carburetor, and it will blow it out. I'll try that quarter turn, may do it.
 
ekywildcat said:
Ok thanks. I'll try the 1/4 turn tomorrow. I think it's in the valves. Key was fine and it doesn't really backfire, it just blows, I can stuff a paper towel in the carburetor, and it will blow it out. I'll try that quarter turn, may do it.
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"stuff a paper towel in the carburetor, and it will blow it out" it means that the inlet valve is still open, so recheck
 

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"And I have the aluminum push rod on the bottom and steel on top"

As far as running this doesn't matter as they are both the same length also it is supposed to blow back SOME thru the carb as that is how they relieve some compression in order for the starter to turn the engine. Also, after checking the IPL, it appears that engine has a camshaft made in segments which have a fairly high rate of failure. I would remove the valve cover and make sure both valves open about the same amount. The exhaust valve cam lobe may be worn to where it is not letting enough air out.

I can send you detailed instructions on how to adjust the valves IF you like, address below.

Walt Conner
wconner5 at frontier dot com
 
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