Shrek 11 #1 Posted January 11 I rebuilt the K181 on my C-85 about three years ago. It's been mowing lawns and plowing snow since then. This summer it developed an issue. It will start up and run as usual but after a few minutes it backfires and then dies. I checked spark - bright blue and fuel - electric pump is pumping. I thought there may be a problem with the exhaust valve and possibly carbon build up. I should note that I found the air cleaner assembly so loose it was shaking around. The two screws that mount it to the carb were VERY loose. This happened earlier this last summer. I pulled the head and found a lot of carbon. Here are some photos... The valve lash on the exhaust valve is .018". Range is .015 - .017". The head has flaking carbon. I want to "de-carbon" the head and clean and lap the valves. Do I de-carbon the piston? Basically, I need guidance on what to do and how to do it at this point. 1 Share this post Link to post Share on other sites
stevasaurus 22,235 #2 Posted January 11 It could be a few things, but the first thing looks to be running rich. The screw on top ot the carb...back out 1/4 turn and see how it runs. You might also check the gap on the points...should be .020...if that is what you have, try .018. Do things one at a time, or you will not know what the problem was. 3 Share this post Link to post Share on other sites
ranger 1,652 #3 Posted January 11 When it dies, try the starter immediately, then see if the engines coasts to a standstill after releasing the key, rather than stopping quickly. I had this problem with my 312-8, it was a sticking exhaust valve, due to excessive back pressure in the muffler, resulting in an overheated valve. It would start again after cooling down! 3 Share this post Link to post Share on other sites
ri702bill 7,360 #4 Posted January 11 (edited) My personal preference to decarbon the head it to warm it - leave it carbon side up on top of the toaster oven when making toast. next, the head goes to the kitchen sink, and give it a good spray down with Oven Cleaner, Wait 5 minutes at the MOST, rinse with hot water and a scrubby sponge - (used to have to do this when my wife was sleeping, otherwise it got too "noisy" ).Use a plastic teaspoon to remove the rest. DO NOT use oven cleaner on the piston!! Piston at TDC - Use a clean cotton rag, spray the rag with carb cleaner until damp - wipe the piston head until clean - repeat as needed. BY hand - turn the flywheel so the piston moves down an inch or so. Wipe the bore. Back the piston up, repeat. spin the motor over - by hand - check for any carbon on the wall - clean if needed. NOW is the time to turn the motor over so that the exhaust valve is the most open. Inspect the sealing edge of the valve and the seat. It has a tougher life than the intake. Wiggle the valve by the head left to right, front to back. There should be almost NO noticeable play. Pitted valve face or seat, too much guide clearance - then it it time for a valve job....... Prior to reassembly - chase the 5/16-18 threads with a good tap. clean out the holes. Same goes for the bolts - clean the threads AND under the head - if they do not clean up - toss them and get new grade 8 bolts.. All this cleaning is necessary to achieve good torque readings. Lightly oil the bolts. The sealing surface of the head is probably not "flat" - there are prior postings on how to the sand it to regain flatness. Use a razor blade on the sealing surface - top of the block. It MUST be clean. Use a new head gasket - preferrably one with the metal "fire ring" on the inner perimeter - that was OE and seals better.... Torque the head IN STEPS in the proper sequence as specified in the Kohler K series engine manual. Off the top of my head, the final torque is 120 INCH POUNDS. Once the engine has run until warm with no load - , shut it off, retorque the head. It may take 4 or more repititions of retorquing to get a consistant 120 in/lbs. The last step is often overlooked or only done once - inviting head gasket failure. ON A BRIGHT NOTE - the top of the piston looks OK - no dents and NO perimeter clean area ring that would indicate bad rings..... Edited January 11 by ri702bill 2 1 Share this post Link to post Share on other sites
Shrek 11 #5 Posted January 12 2 hours ago, ri702bill said: My personal preference to decarbon the head it to warm it - leave it carbon side up on top of the toaster oven when making toast. next, the head goes to the kitchen sink, and give it a good spray down with Oven Cleaner, Wait 5 minutes at the MOST, rinse with hot water and a scrubby sponge - (used to have to do this when my wife was sleeping, otherwise it got too "noisy" ).Use a plastic teaspoon to remove the rest. DO NOT use oven cleaner on the piston!! Piston at TDC - Use a clean cotton rag, spray the rag with carb cleaner until damp - wipe the piston head until clean - repeat as needed. BY hand - turn the flywheel so the piston moves down an inch or so. Wipe the bore. Back the piston up, repeat. spin the motor over - by hand - check for any carbon on the wall - clean if needed. NOW is the time to turn the motor over so that the exhaust valve is the most open. Inspect the sealing edge of the valve and the seat. It has a tougher life than the intake. Wiggle the valve by the head left to right, front to back. There should be almost NO noticeable play. Pitted valve face or seat, too much guide clearance - then it it time for a valve job....... Prior to reassembly - chase the 5/16-18 threads with a good tap. clean out the holes. Same goes for the bolts - clean the threads AND under the head - if they do not clean up - toss them and get new grade 8 bolts.. All this cleaning is necessary to achieve good torque readings. Lightly oil the bolts. The sealing surface of the head is probably not "flat" - there are prior postings on how to the sand it to regain flatness. Use a razor blade on the sealing surface - top of the block. It MUST be clean. Use a new head gasket - preferrably one with the metal "fire ring" on the inner perimeter - that was OE and seals better.... Torque the head IN STEPS in the proper sequence as specified in the Kohler K series engine manual. Off the top of my head, the final torque is 120 INCH POUNDS. Once the engine has run until warm with no load - , shut it off, retorque the head. It may take 4 or more repititions of retorquing to get a consistant 120 in/lbs. The last step is often overlooked or only done once - inviting head gasket failure. ON A BRIGHT NOTE - the top of the piston looks OK - no dents and NO perimeter clean area ring that would indicate bad rings..... I appreciate the explanation on getting rid of the carbon. Thanks! I'll also check the gap on the points. Should I lap the exhaust valve? Share this post Link to post Share on other sites
8ntruck 6,399 #6 Posted January 12 (edited) On 1/11/2024 at 4:08 PM, stevasaurus said: It could be a few things, but the first thing looks to be running rich. The screw on top ot the carb...back out 1/4 turn and see how it runs. You might also check the gap on the points...should be .020...if that is what you have, try .018. Do things one at a time, or you will not know what the problem was. Wouldn't backing the mixture screw on top of the carb make the mixture richer? Seems like it would need to go in a 1/4 turn to lean it out a bit, or am I all wet? Edited January 13 by 8ntruck 1 1 Share this post Link to post Share on other sites
ri702bill 7,360 #7 Posted January 12 7 hours ago, Shrek said: Should I lap the exhaust valve? IF the valve face and the seat are not pitted to a point where a valve job is required, it would not hurt - BUT - must be done with cautiion. You do not want any of the lapping compound grit to get below the valve. Slow speed, by hand, not using a cordless drill! Two benefits - it leaves a telltale "ring" on both the valve and seat showing the sealing pattern. And, it just might sink the valve enough to loose .001 in height, bringing the valve clearance down to .017..... maybe. You have to remove ALL the grit. 3 hours ago, 8ntruck said: Wouldn't backing the mixture screw on top of the carb make the mixture richer? Don't forget that the mixture needle is hollow - there are 2 teeny-tiny holes in it. It is the air bleed for the mix and must be kept clean to flow air... Share this post Link to post Share on other sites
953 nut 51,881 #8 Posted January 12 14 hours ago, ri702bill said: leave it carbon side up on top of the toaster oven when making toast. next, the head goes to the kitchen sink, and give it a good spray down with Oven Cleaner, Wait 5 minutes at the MOST, rinse with hot water and a scrubby sponge - (used to have to do this when my wife was sleeping, otherwise it got too "noisy" ).Use a plastic teaspoon to remove the rest If I did that you would be reading my obituary! 17 hours ago, Shrek said: It will start up and run as usual but after a few minutes it backfires and then dies While you are at it you should replace the ignition condenser, as they reach the end of life they will have an intermittent internal short causing the ignition to cut out then return. 1 1 Share this post Link to post Share on other sites
stevasaurus 22,235 #9 Posted January 12 I might be wrong on backing the screw to make it leaner...I am thinking that means more air. Share this post Link to post Share on other sites
953 nut 51,881 #10 Posted January 13 6 hours ago, stevasaurus said: I might be wrong on backing the screw to make it leaner...I am thinking that means more air. Clockwise runs the needle into the seat further restricting the amount of fuel coming through the jet. Share this post Link to post Share on other sites
