SEARS 16.5 KOHLER,Backfire on start

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SEARS 16.5 KOHLER,Backfire on start

JOHN Tractor is 2yrs old,less than 50 hrs,Backfire, will not start,when it does runs fine,Replaced wooddruff key,sams unit,Carb,no change,new plug,airfilter,fuel filter,now suspect gov setting or Valve train.Any Advice I am stuck.
Jack check for possible short in wiring,safty switches,if carb has a fuel shot-off solenoid this could cause problem also Jack
John Kissell Jack,Thank you for reply I have isolated the white kill lead from sams to the rest of tractor even bypassed mower switch and clutch brake switch the new card I installed today had new fuel shut sel on it,that keep leading me to valve bend or lifter or plush rod but can not figure why rockers are not the adjustable type

Carl Fickling John,
I believe this engine uses hydraulic lifters, so the values are not adjustable. You can also download the service manual for this engine for free at the kohler web site.
the manual is at

Lance John you say when the tractor does run it runs fine. That would lead me to believe your valvetrain is fine. If there were problems in the valvatrain the motor would be making a knocking sound. Sounds to me like an ign. problem. The timing sounds like it maybe out of whack. I would check to see if it is adj. or not. Good luck!
john Carl,You folks are great,I did down load the manual,that is how I have got this far with the tractor,its great they made it avail.I keep reading and re-reading trouble shooting section,it talks about ACR in the last page but it would not run at all or stater would not turn engine if it was out of wack if I am reading it right.
John lance,Thank you,I could have wrong woodruff key and I agree with you about timming but only one way to install flywheel and when it broke which stared all this it was 180 out old and new key looked the same,my current thinking is intake valve is holding open a little,and at the start of last year mowing,I did not want to hear what I thought might be more engine noise or quiet raddle in engine,wanted to think it was engine starting to break in.
Carl Fickling John,
You are reading it right... The ACR is NOT your problem. You did say you replaced the SAM, but did you replace the ignition module? This could also be causing the backfire. Is the gap set at about 10 thousandth at both gaps? I usually use a buisness card in the slot and tighen down both screws. You MUST also be sure the the magnet on the flywheel does NOT touch the core of the ignition module at all.
Also try removing the air filter, and poring just a LITTLE gas into the carb input, to see if it will start with the exta fuel. I like it best to remove the air filter house, and use several large nuts for spacers and bolt the carb on with out the housing. This way you can see the carb, and where the choke and throttle are at, and make any adjustments with the idle mixture and idle speed.
Also the SAM REQUIRES at least 7.2 volts to work correctly. If your little battery is even a little weak it may not be putting out the 7.2 volts while CRANKING. Try using a good large automotive type battery to crank it with, this way you will be sure to get the 7.2 volts to the SAM module.
If you need anymore ideas, just yell!!

John Carl,I have not replaced coil and the old and new sams is getting 7.2 while cranking,I just open the valve cover and intake rocker can be moved with light finger pressure I am thinking I with forms help,may have nailed it valves are moving in and out as I turn flywheel when closed I can move the intake rocker arm and not the exaust want to look at push rod (bend)or (bow)stud and the arm will let you know again thanks for the help
John Carl,just nailed the trouble hour ago,Sears tractor has run and different start lead from the Ign switch,Voltages would read right.but if the run lead has a come and go open in the switch or the lead,voltage will drop come back causing backfire like I used to do with my fist car when I was 16,buy pass to new dash mounted toggle switch and all trouble gone tractor runs lke new, valves were ok

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