I recently bought a used riding lawnmower with a 14.5 HP Briggs and Stratton OHV model number 287707 engine. The engine starts and idles fine but when I apply apply the throttle the engine RPMs don't increase and it just kind of make a popping sound thru the air intake. Could this be a valve problem? Sorry about the non-technical description. I would appreciate any help.

Thats what it sounds like,Adjust the valves cold,Remove the valve cover screws and lightly tap the valve cover and it may pop off without damaging the gasket.Remove the spark plug and rotate the engine over by hand until you reach top dead center compression stroke,Take a small screw driver and insert it in the plug hole and touching the top of the piston,Rotate the piston past t.d.c. 1/4 inch and adjust the intake valve .003 to .005 and the exhaust .005 to .007. I go in the middle myself with .004 and .006 .
If this doesn't solve the problem just post back.

 

It has a bit too much clearance on the exhaust valve but i don't see how to adjust it. There is only one nut on the valve stem. Do I have to replace the valve? Thanks.

 

It has a bit too much clearance on the exhaust valve but i don't see how to adjust it. There is only one nut on the valve stem. Do I have to replace the valve? Thanks.

No !!! On the inside of the nut is a allen set screw loosen it first then adjust the nut and retighten the set screw while holding the nut.
It may take a couple times to get it right because when you tighten the set screw it throws the adjustment out.

 

No !!! On the inside of the nut is a allen set screw loosen it first then adjust the nut and retighten the set screw while holding the nut.
It may take a couple times to get it right because when you tighten the set screw it throws the adjustment out.

Sorry to miss inform you,The set screw in the center of the nut takes a Torx bit to loosen.

 

Thanks, I adjusted the valves and it runs better but I can only apply about 3/4 throttle before it begins the popping and shaking again. Maybe I need to ajust the timing now? How do I do that?

 

Thanks, I adjusted the valves and it runs better but I can only apply about 3/4 throttle before it begins the popping and shaking again. Maybe I need to ajust the timing now? How do I do that?

There is no timming adjustment on this engine,The flywheel key is what maintains the proper timming,You can check and see if it may be partly sheard by removing the top cover then the screws holding the grass screen on then the round plastic disc,Down in the cup you will see the flywheel bolt.
Take the spark plug out and rotate the engine by hand to TDC compression stroke,Rotate past TDC 1/4 turn and feed about 6 or 8" of #5 recoil rope into the plug hole making sure to leave enough sticking out to remove it when done. With the rope in the cylinder rotate the flywheel counter clock wise until it stops and remove the flywheel bolt.You now can look at the inside and see if the notch in the crankshaft is algined with the notch in the flywheel,If it isn't it needs to be replaced.Use a puller and remove two of the screws holding the plastic fan in place to get the flywheel off,Once the new key is installed and the bolt just snugged rotate the flywheel clockwise just enough to remove the rope then rotate counter clockwise 1/2 turn from there and reinstall the rope in the cylinder and torque the flywheel bolt to 85ft. lbs.
before total reassembly take any buisness card and check the clearence between the coil and magnet on the flywheel and adjust if needed.
If the key is fine its possible the previous owner only ran the mower around 3/4 throttle and it built up a little too much carbon on top of the piston and valves and when you got it and started running it wide open a piece of carbon broke loose and stuck under a valve,In this case remove the head and clean all the carbon deposits and check the valves and reassemble.

 

Excellent information, thank you. I'll give it a try. It appears my next move is to buy a battery.

 

That recoil rope trick really works, I've done that before myself thanks to what restrorob posted. Just follow his directions, it's a snap.