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Discussion Starter #1
Hey everyone I am new here and I really like this fourm so I think Ill stick around. Ok so I have this 87 briggs 11hp vertical shaft on a lawn chief mower. I had it running but it runs very badly and shoots puffs of gas out the carb on startup and at low idle. When the engine is running at high idle it seems to bog and governer hunt. I look down into the carb and I can see gas shooting out of the jets. I originaly thought it was a gunked up valve so I look off the head and cleaned both valves with the wire wheel and lapped. My valve clearance at 1/4 past TDC is .005 intake and .010 on exaust which is what its suppost to be. But the engine is still doing the same thing! The carb is perfect, I soaked it and cleaned it out real good with my compressor. It gets a nice deep blue spark and the flywheel key is in right. Does anyone know what my problem is. Help is very apperciated. P.S anyone else here and young as me haha!
 

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Discussion Starter #3 (Edited)
Ive adjusted the main and low jets and the engine seems to runs better the farther I close the main jet but it still won't run right and dies when the jet completely closes. Briggs says the main jet should be at 1 1/4 turns and the engine wont even stay running at that setting.
 

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Set the low speed needle with engine at idle. Then adjust high speed with engine running at full power. If this doesn't smooth engine out, I would think you have a intake valve sticking in the valve guide.

It would help if you posted model number and code. I am assuming it's a 25000 series being a 11hp.
 

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Discussion Starter #7 (Edited)
Model Type code
253707 0197-01 87033110

The intake valve is closing fully from what I can tell, I lapped the valves with my briggs and stratton valve lapper and checked the valve clearance. I plan on working on it tonight but im not sure what else to look for.
Oh yes also I noticed that I never had to choke the engine to get it started, me and my neighbor noticed that was werid.
 

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justin3 said:
Oh yes also I noticed that I never had to choke the engine to get it started, me and my neighbor noticed that was werid.
No thats not really weird. If the weather is warm enough you might not have to choke this engine to get it started. If the engines ever been apart the valve timing might be off a tooth or two, also check the flywheel key a partially sheared key could advance the timing enough to cause a little blow back.

I usually find insufficient clearance on the intake valve on these engines but if you have the proper lash that should not be the case. Was the intake valve seat tight in the block?
 

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Ok I'am going suggest 2 more things and after that I don,t know what else to do. ( I'm stumped )

When you worked carb did you install a carb kit or just clean? ( If you installed new carb kit disregard #1 )

1. Check needle and seat in carb for wear that would not let the fuel flow to shut-off.

2. Check float height setting. With carb upside down measure from base of carb to top of float ( this is really bottom of float because carb is upside down ) Should be equal measurement on both sides. ( Needle and Seat side to straight across on float ) Make sure needle is seated.

Hope this make since.
 

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Discussion Starter #10
Ok guys thanks for all your help, today I took apart the carb and found 1 problem, the jet screw that screws into the top of the carb was slightly bent so I replaced it. Now the engine runs somewhat better but still governer hunts. I can clearly see gas being blown back out the carb so I now know this is a timing problem. I already checked the flywheel key and it is perfect, so I will take the head off and inspect the valves. If that doesnt solve the problem then I will break open the engine and check the cam timings. Can someone tell me how to check valve lash so im sure I am checking it right? Thanks guyz. I will have a youtube video up soon for you also.
 

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justin3 said:
Can someone tell me how to check valve lash so im sure I am checking it right? Thanks guyz. I will have a youtube video up soon for you also.

You have to remove your carburetor and the oil breather assembly. Just check the clearance between the lifter and valve stem with the engine at TDC or just slightly past TDC. In a lot of cases where I was getting blow back on these engines, I generally find little or no lash on the intake valve. Over a period of time the wear on the valve seats and facing as well as valve stem stretching occurs and the lash disappears. There have also been instances where the valve seat itself came loose in the block and clearance was lost. If the seat is loose you can have blow by even if there is clearance.
 

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Discussion Starter #12 (Edited)
30yeartech I do remember once on a 3.5 hp briggs, I found the valve seal broke loose and jammed the valve open lol so I guess something like that is possable on this engine, I will check the valve lash and seats tommarrow and hopefuly get back to you. Thanks

EDIT:: http://www.youtube.com/watch?v=a9ME7hhc60M
theres the video for you guys, it shows what it happening.
 

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Discussion Starter #13
4/11/07
Ok guys I just got out of the garage, and I found 2 problems with the engine. Number 1 the intake valve lash wasnt enough so I filed the stem down to .005 clearance. Next there was scoring and pitting on the exaust valve so I have to find another one. I had to order some seals so when I get it back together I will let you know the out come.
Thanks alot!
 

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I saw your video, and I just want to mention that you should not run your engine very long without the shroud on it. The shroud directs the cooling air around the cylinder and the engine can overheat very rapidly without it.

It really sounds like an intake valve problem to me, and you might want to check and make sure the governor is adjusted properly.

:thumbsup:
 

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Discussion Starter #16
Ok guys sorry for the time waiting but I was delayed due to recored floods here in CT lol basement is repaired now so back to Internet life. I found the valve lash on the engine was .002 to much so I ground it down and now the engine runs good at .006 intake and .011 exaust. To grind down the stems I used a hand file, what is the best thing to use? Thanks so much guys, you solved my headache.
 
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