Small Engines (Lawn Mowers, etc.): Riding Mower, feeler gauge, compression stroke

Question
Hi Paul, you answered 2 questions earlier this week for me about my 2004 troybilt pony with a B&S 17.5hp engine concerning valves.  Today I adjusted the valves.  The engine cranked up and ran great until I engaged the PTO to the blades.  When I let the deck down to mow the engine began to speed up and slow down. Will over tightening the valves cause this? I used a 004 feeler gauge with a fairly snug feel.  I lifted the deck up and the motor ran smoothly again. I check the distances the rocker arms were moving to see if the cam was working and they looked right. The engine has never done this racing up and down before.  Do you think that I may have gotten the valves too tight.  I eyeballed the distance the piston went past TDC instead of measuring it. I may have put the piston down to far.  The mower ran as fast as it was supposed to and the gears shifted ok. I sprayed the linkages with WD40 while I had the sides and front off the mower. I really don't think this is a carburetor issue. If you can enlighten me as to what you think the problem is, I will appreciate it.

Answer
Hi  

here is web site for parts -assy diagram
http://www.briggsandstratton.com/support/?NTT=31c707-0154-e1

i do think you should adjust valves again , @ 1/4 past tdc  on compression stroke
( that is 1/4 inch down the bore on the power stroke ) adjust inlet to 0.004 Thou and just a very slight drag on gauge, and adjust  ex to 0.005 thou  same deal just slight drag.  hold this position and tighten  nuts.

physically measure distance  from top of piston to a point on cyl head  note this measurement
add 6.35 mm to that measurement  and run  the piston down the bore till the new mark lines up @ the point you noted on the head  ( ie  cyl rocker cover flange)


make sure the deck mandrell and blade spindles bearings are not binding or or semi siezed
and nothing is binding blades in the deck

check fuel flow from tank to fuel pump and from  fuel pump to carb it should be full flow out of hose without any spasmodict/erratic flow.    

check carb is good and the carb is clean and set   taking note of all jets and openings ie  air bleeds and progression ports and main jets and emulsion tube
because while engine is runing under no load fuel delivered via idle and transition port
but under load  fuel is delivered via main jet and emulsion tube

so check carby carefully for anything restricting fuel through main jets etc  from memory this carby could be a large walbro  or a nikki type

if this is ok  the could very be  governor adjustment
do this by hold thottle link that goes to throttle plate @ full open , hold  at this position , loosen the governor shaft clamping nut and turn the governor shaft clockwise fully and tightn clamping screw.

have look , let me know

hope it helps

check out www.briggsandstratton.com/support/maintenance howto

its a good site  


cheers paul  hope it helps