Small Engines (Lawn Mowers, etc.): B&S horiz. twin wont start., intake valve, line filter

Question
Hi,

I have an 18hp B&S engine in an Agway lawn mower.
Model: 422707
Type: 152-01
Code: 9403055B

For no apparent reason one day it would not start, I checked the fuel lines found a crack (no leak) and replaced all the line & filter, and put new plugs in it.  Sometimes it fires but won't run.  Checked the magneto and it seems fine unless it has a weak spark to one plug.  Now the weird part, I pulled the right side plug to check for spark, grounded it on a piece of tin mounted to the engine, got spark, and the motor started?  Tried it with the other side and it won't start.  When the plug is pulled from the side that won't start it is not soaked but smells of gas.  It will start and run good for about 60 seconds when clean dry plugs are installed, then back to the same deal.  Side note, from time to time the carb will spit gas out of the top (air filter has been removed.)  Is there anything else to the ignition?  Can
the coil work but not be strong enough (spark is blown out by compression)?  Can one wire be bad and the other good (the reason I could get it to run on one cyl)?  Could it be a sticking intake valve?  Any info or ideas would be appreciated.

Thanks,
Ryan


Answer
I'd start with verifying that the compression in each cylinder is close.  Next I'd go ahead and go through the carburetor as you seem to maybe be getting too much fuel.  First you might want to pull and plug the fuel line and drain the bowl.  Then try a little ether and see if the engine will hit.  That would isolate whether it's carburetor or possibly ignition.  Also, check the oil and smell it for gas just as a precaution.  Let me know what you find and we'll go from there.  Thanks, PK.