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Junk collector
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Discussion Starter · #1 ·
One step forward and two steps back. Today I tried to start my B&S 5hp horizontal on my tiller and its now "coughing" back through the carburetor. Its not backfiring as its not hitting at all, it seems to be coughing compression out through the carb. I'm thinking I have a burned intake valve thats not seating all the way or leaking. After I rebuilt the carb it seemed to be running ok, as well as a tired 21 year old engine can. Does this seem plausible? Any other suggestions?
 

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Add about a teaspoon of oil to the cylinder- this will seal any leaks and hopefully give you enough compression to get started. A very common problem on this engine is loss of intake valve clearance due to dust ingestion- the purpose of the oil is to mask this problem.
 

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Junk collector
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632 Posts
Discussion Starter · #3 ·
Thanks, I'll give it a try. One of my buds says it could be a sheared flywheel key or a bad spark plug. While anything's possible do these seem likely in this case?
 

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Probably the valve is sticking in the open position..I'd add the oil as suggested,it may compress and help force the valve shut and then it might fire up..if not,you can take off the valve cover or breather cover and use a screwdriver to pry the valve spring carefully and get the valve to close,also spray penetrating oil on the valve stem...

If the valve is rusted bad,you may have to take the cylinder head off to try and free it up in the guide..you can turn the valve with pliers that have the jaws taped up to prevent damage to the critical valve face areas..I've had to resort to using crowbars to pry out a very stuck valve in an engine like yours before,and use a drill bit to clean up the valve guide hole!..and replave the valve with another "good used" one I had..
 

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Junk collector
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Discussion Starter · #7 ·
Last weekend I took the engine apart. The valves were very dirty, I cleaned them off and lapped them. They now seem to seat alot better than they did, I also cleaned out the cylinder head. I didn't see any obvious problems. Hopefully it will start and run alot better once I get the new head gasket.
 

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On my singles, after shutting them down, I turn the crank by hand into the compression stroke. That way I know moisture and dirt won't get into the combustion chamber or the valve stem area. I turn the crank until I feel the piston reach TDC (the compression resistance is gone).
 

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Junk collector
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Discussion Starter · #9 ·
I got the engine assembled and mounted on the tiller on monday. It started and ran, unfortunately it doesn't run very well because I still can't figure out how the stupid spring that goes from the throttle control to the governor arm goes back on. I have no throttle control and the governor just kind of does its own thing. The B&S manual only has "typical" pictures so its going to be a matter of trial and (mostly) error. Maybe by next spring I'll have it figured out.:banghead3
 
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