Snapper w/Briggs won't start/run

Returning Snapper SR-140 rear-engine electric start rider, Mdl:3312513BE, with 12.5hp B&S to service. Unit has been idle and outdoors for 4 yrs.

Replaced fuel lines/filter,etc. Cleaned gas tank. Removed Walbro LMT-5 carburetor and cleaned on site. Unit started and ran, but very roughly above idle. No muffler at all at that time.

Had carburetor professionally cleaned/rebuilt. Installed new muffler & installed rebuilt carburetor. Changed oil. Now unit will not start at all. Spits/sputters, but will not run. Removed spark plug, previously cleaned, and it appeared to be fouled/wet. Recleaned & installed. First few seconds of start attempt sounded like they were going to be successful but didn't quite make it and unit returned quickly to no start/run condition. Because of plug's previous wet condition, I suspect that I'm getting too rich of a fuel/air mixture to support combustion. Unfortunately, I've not been able to find any information on what initial carburetor adjustments should be. I have two adjusting screws, one obviously an idle speed adjust. The other I assume is a rich/lean adjust. So, I need some tech assist on what may be wrong and corrective measures.

One theoretical question. The thing actually ran w/o a muffler, right? Could the installation of a muffler, and the attendant backpressure, actually have screwed things up to the point that it now won't even start? Thanks for any help.

 

intial carb settings are 1-1/2 turns out from lightly seated

 

Working on it this am, discovered that if I removed the air filter it would start right up though it still ran very roughly. Thinking that the filter was dirty (even though it didn't look that way) I soaked the element in soapy water for a couple hours and let it dry. I then adjusted the mixture screw to the prescribed initial setting and started the mower without the filter. The engine ran just as rough as before. More interestingly, I discovered that placing the filter element back into its housing would choke the engine right down. Looking into the air intake plenum, I discovered gasoline residue, as if the engine were throwing vapors out the carburetor instead of sucking them in! That can't be right! Is it possible that what I'm seeing is an air breather malfunction?

 

From your description of it spitting gas out, it might be the intake valve isn't quite closing all the way. After sitting for 4 yrs this is entirely possible.
JMHO,
Mike

 

Assuming you are correct, and that had ocurred to me as well, what is the fix?

 

Take the head off and have a look, or do a leakdown test to see if the valves are seating or not. I'm not sure you don't still have a carb problem though, but doing a leakdown test would indicate or eliminate the valves as a problem so you can narrow it down.

 

Heading out now to take a look. Will keep you informed. How is a leak test performed?

 

Having already replaced the head gasket, I was very surprised at what I found when I removed the head. The new gasket was ruined, the metal gasket coating damaged in several places. I found that even when seated the intake valve could be turned simply with a little thumb pressure. Weak valve spring? I'm thinking that at the very least the engine needs a valve job and who knows what else. I'm beginning to see big dollar signs and wondering what a used rebuilt engine might cost. I have neither the tools nor the expertise to do a proper overhaul myself.

 

With the intake valve fully closed, you can still turn it easily? If so, the valve stems need to be ground to obtain proper clearance. Not a ridiculously expensive job.

 

Spoke w/my brother, a former stockcar engine builder, and he echoed the simplicity of the job, telling me how to do my own valve job. He went through the whole lapping procedure, grinding the stems, etc. Actually sounds pretty easy. I have to find a spring compressor and lap tool, but other than that have all I need. Appreciate all the advice.