I was given a Poulan tractor with a 13.5 HP B&S engine. It was thrown in with the purchase of a home. Previous owner said it never ran very good. I found it was "puffing back" thru the carb when cranking. I checked the valve operation and found that the intake valve was not closing fully until after top dead center (right at the beginning of the power stroke). The Briggs manual says to check the valve clearance with the piston .250" below top dead center on the power stroke. I removed the valve and machined the stem to get about .012 clearance. I lapped the valve/seat. Now the starter won't crank the engine (too much compression?). I pulled the engine, removed the bottom of the crankcase. The timing marks appeared to be correct when I opened it up. It looks to me like the intake cam lobe may be installed on the camshaft backward. there is a bit of a raised section on the profile on the downslope of the lobe which would could hold the intake valve open during all or part of the compression stroke. If it were on the upslope part of the lobe it might be there for scavenging purposes, but I don't see any reason for it on the other side. It is a 28R707 model. Does anyone have an idea what the cylinder pressure might be when cranking? Anyone have a similar problem with this model engine? It won't kill me to junk this thing, but I thought it would make a good trailer puller slash trail mower. It's in good shape other than the engine. Any thoughts????
