Small Engines (Lawn Mowers, etc.): McLane Briggs and Stratton valve timing, briggs and stratton, oil results

Question
This engine has not been apart, but noticed with head off, position of piston in relation to valve timing seems off.  On overlap it seems piston is coming up when intake valve starts opening.  Is cam timing relatively this mild to do that?  Also, with carb off and hand over intake, it pops off my hand.  With carb on and hand over intake of carb, the choke (pull out type) pops back and forth...rat tat tat.  Something like that, which would indicate compression backing past intake?  Sounds odd to you???l

Answer
HI LES  

IF ENGINE NOT BEEN OPENED BEFORE
HAS THE ENGINE HAD REGULAR OIL CHANGES AND BEEN RUN WITH CORRECT AMOUNT OF OIL  ?

HOPE ENGINE HAS NOT BEEN RUN WITH INSUFFCIENT OIL  OR TOO MUCH  OIL  - RESULTS FOR BOTH CAN BE THAT SAME !

VALVE TIMMING -  INLET STARTS OPENING SO MANY DEGREES   IE  15 DEGREES  BEFORE TDC  
AND INLET CLOSES SO MANY DEGREES IE  30 DEGREES  AFTER BDC

EX VALVE STARTS OPENING SO MANY DEGREES IE  28 DEGREES  BBDC
AND CLOSES  SO MANY DEGREES IE  10 DEGREES ATDC  

THE NUMBER OF DEGREES  BETWEEN  INLET OPENING AND EX CLOSING  NEAR TDC  IS VALVE OVERLAP
AND IS REASONABLY MILD    IE   15 DEGREES BTDC  AND  10 DEGREES ATDC = 25 DEGREES OVERLAP
THIS IS EXAMPLE ONLY  

IT SOUNDS LIKE YOU MAY HAVE A STUCK  INLET VALVE IN THE GUIDE  AND IS ALLOWING A BACKFLOW OF FUEL AND PRESSURE TO CARB  , AND POSSIBLY A BURNED / LEAKING VALE / SEAT

PAY TO CHECK VALVE CLEARANCE  IF ENGINE IS SIDE VALE UNIT AND BRIGGS    GENERAL C/CLEAR IS  
0.005"  INLET  AND 0.007: EXHAUST   IF  ONE IS EXTREMELY WIDE THEN STUCK OR STICKING VALVE IN GUIDE ,  BUT  IF ONE OR BOTH VALVE CLEARANCES ARE TIGHT  OR NONE  
TIME FOR  VALVE GRIND / RECUT SEATS   PROVIDED  VALVE MARGIN IS ABOVE 1/32 MINIMUM  DISCARD VALVE IF MARGIN IS 1/64 "  OR HAS GONE TO A SHARPISH EDGE  MAKE SURE STEM IS NOT  WORN OUT

CAN YOU SEE ANY SIGNS OF SCORING OR O/HEATING  OR MARKS ON CYLINDER BORE ?

WHEN CYLINDER HEAD WAS ON AND YOU PULLED THE ENGINE OVER WAS THERE A CHUFF CHUFF NOISE COMMING FROM EXHAUST , WHICH MAY INDICATE POOR EX VLAVES AS WELL

CAN YOU SEE ANY SIGNS OF A BLOWN HEAD GASKET  - BLACK , BURNT,  CYL GASKET SURFACE ?

MAKE SURE THE SPRING THAT KEEPS CHOKE PLATE OPEN IS IN PLACE

UNIT  DOES SOUND VERY MUCH LIKE NEEDING  VALVE SEATS RECUT AND REFACED OR REPLACED
, AND CYL HEAD GASKET  AND VALVE CLEARANCE SET

CAN YOU LET ME KNOW MODEL AND TYPE CODES OFF ENGINE  COVER  , I WILL TRY HELP SOME MORE

CHEERS PAUL