bkarp@roadrunner.com 5 #1 Posted June 30, 2023 I have a 312-8 tractor with a k12s kohler engine.After 40 min. of cutting grass it stops and will not start until a 3 hour cool down.Items replaced have been carb,fuel pump,fuel lines magneto. It still has spark when it will not start.do not know what else to do. thanks for any help. Share this post Link to post Share on other sites
ri702bill 7,481 #2 Posted June 30, 2023 (edited) 23 minutes ago, bkarp@roadrunner.com said: It still has spark when it will not start. Welcome! Are you using an inline spark checker to verify spark?? When it dies out, let it cool and pull the spark plug. I have a high usage hours 702 that will oil foul the plug in an hour, but will still run until you shut it off. A spark checker shows it has spark, but the spark follows the wet carbon at the tip, goes to ground. Pull the plug and clean it with carb spray, reinstall, it starts up fine... Another annoying possibility is a clogged gas cap vent. Does it have a see through gas filter.?? Look at it right after it starts and when it dies. Both should look about the same... if the filter is "dry" when it dies out, it says there is a fuel delivery issue... You replaced the fuel pump - with a new plastic one from an "offshore source"??? .. If so, pull the fuel line going to the carb, pull the coil wire at the plug so it will NOT start, and crank it over. You should see a constant pulsing of fuel coming out... you will not see a constant stream. Edited June 30, 2023 by ri702bill 1 Share this post Link to post Share on other sites
ranger 1,666 #3 Posted June 30, 2023 My 312-8 with the Kohler Magnum engine did this after I fitted a stainless steel muffler. The exhaust valve was sticking, due to excessive heat retention, (apparently an issue with early Magnum engines, necessitating a dealer recall to increase the guide size slightly). After cooling down, the valve would close and the engine could be re-started. Next time it happens, spin the engine over on the starter and see if it has compression or not? Mine would coast to a stop on releasing the key, instead of stopping almost immediately! 3 Share this post Link to post Share on other sites
ri702bill 7,481 #4 Posted June 30, 2023 3 minutes ago, ranger said: due to excessive heat retention, That teamed up with the valve stuck open, unable to sit on the seat can lead up to a warped valve...... 1 Share this post Link to post Share on other sites
gwest_ca-(File Mod) 10,548 #5 Posted June 30, 2023 If the fuel checks out check the valve clearances and adjust as necessary. Add a shot of Marvel Mystery oil to the fuel which will lube the valve stems. A shot of 2-strojke would do the same thing. 2 1 Share this post Link to post Share on other sites
ri702bill 7,481 #6 Posted June 30, 2023 30 minutes ago, gwest_ca said: If the fuel checks out check the valve clearances and adjust as necessary. Add a shot of Marvel Mystery oil to the fuel which will lube the valve stems. A shot of 2-strojke would do the same thing. AND... you can fog for mosquito control at the same time !! 1 Share this post Link to post Share on other sites
bkarp@roadrunner.com 5 #7 Posted June 30, 2023 thanks for the input about my tractor,plug is clean,light brown in color, gas cap is vented and working,i did put on the plastic fuel pump,could that be the problem, i will pull the line off next time i use it and see if it is pumping fuel.Other wise it sounds like it could be a sticking exhaust valve. thanks for the help. brent 1 Share this post Link to post Share on other sites
ineedanother 1,366 #8 Posted June 30, 2023 Any signs that the muffler might be red hot when it shuts down? I know that could be difficult to tell in the daytime but a sticking exhaust valve can cause that as ignition isn't contained in the cylinder bore if the valve is open. 1 Share this post Link to post Share on other sites
