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The Small Engine Doctor
The Small Engine Doctor, Small Engine Technician
Category: Small Engine
Satisfied Customers: 81
Experience:  Over 30 years experience repairing & rebuiding 2&4 cycle engines, All brands and configurations
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My John Deere LT160 lawn tractor wont start. The Kohler engine

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My John Deere LT160 lawn tractor won't start. The Kohler engine (Model CV460S) doesn't seem to be getting any gas to the spark plug. It just backfires after I crank the engine for about 10 seconds. When I pull the sparkplug, it's bone dry. Gas flow from the fuel pump to the carb is good. I took the carb off and cleaned everything with carb cleaner, checked the operation of the fuel bowl solenoid and made sure the plastic float isn't cracked or hanging up and there's no dirt in the intake valve. What am I missing here?

Hi Gary, this is Dave, The Small Engine Doctor. The symptom, taken by itself indicates a substantial vacuum leak, or failure to produce enough vacuum in the intake port to properly charge the cylinder.Obviously something happened that caused you to do this work which you don't mention but regardless, lets get you fixed up!!! You commented that the fuel pump was OK. Did you try the pump while it was installed? Often if you operate it off of the engine it looks great because you can operate the push rod all you want but installed, it's limited to the amount the cam will lift it, so thats one thing you might have to check. The biggest thing thou is the "heat deflector" as they call it. It's more like a heat insulator. It's that plastic "thing" that is between the carb and the head and I've seen these things give people more grief (myself included) than you would believe. What happens over time is that they warp and become distorted. It looks OK so you put it back with a new gasket and forget about it and then go nuts for a couple of days. If you look at it very carefully you'll see the warpage. I'm NOT SAYING THAT THIS IS THE EXACT PROBLEM but, it often is!! You can resurface with a belt sander, WITH GREAT CARE and a well used belt because remember, its plastic. Put it all back together with a little Perma-tex on every mating surface and see what happens!!!!


If this answer fixes your problem, you can go ahead and click the "accept" button and whatever feedback would be greatly appreciated. I'll be here for any additional help if need be. Sincerely, Dave

Customer: replied 9 years ago.
Hi Dave! Seems like it's just one problem after another with this tractor. I did check the fuel pump while installed on the tractor, and I've got plenty of gas flowing to the carb. I pulled the heat shield off this time around and there's no warpage at all in it. However, it WAS flopping around loose against the head after removing the carb assembly, so I'm sure it wasn't sealing very well. There was no Permatex on either of the gaskets at all. I'll have to wait till Monday for the John Deere dealership to reopen before I can get a new heat shield and gaskets. I'll get back to you as soon as I get everything reassembled. Thanks!

Hi Gary, While your waiting till Monday why dont you do this little experiment. Get a fresh piece of sandpaper, preferably wet-dry about 220-320. Put the paper down on a very flat surface (something that is Formica covered works well). Take the heat shield and while holding the paper with one hand, rub the heat shield in a circular motion with the other. A little oil works good also. Do this for a few seconds at first . Then clean it off and take a look. The high spots will show up and so will the low. The low spots is where you're leaking.

As far as it flopping around, its the carb that holds it tight against the head or I should say when you tighten the carb, it should hold the insulator tight and there should be gaskets on EVERY mateing surface. Let me know how you make out !!

Customer: replied 9 years ago.
Hey Dave, sorry for the delay! The dealership had to order the gaskets and heat deflector and I installed them today. Now I'm getting gas to the spark plug again. Unfortunately, while reinstalling the regulator to the engine shroud it sparked, and now I don't have any spark at the spark plug. Seems like I may have shorted out the regulator or blown a fuse somewhere. Where do you suggest I start looking to fix THIS problem?

Hi Gary, Thats hard to say. One things for sure. When working on anything where your going to have to mess around with wires, the first thing you have to do is disconnect the battery. I would start by looking "under" the dash, behind the instrument panel. There are fuse, but there are also a number of relays and things like that. Look for anything that looks burnt and smells. Actually, the regulator is not on the same circuit as the ignition coil, unless you crossed some wires in the harness. What you really have to worry about is the alternator, which is connected DIRECTLY to the regulator and is located under the flywheel. One "saving grace" is that the wire that probably sparked is the one marked (and connected to through the switch) "battery" and theres probably a fuse there somewhere. Just start looking around at all of the wires and harnesses and you'll probably find something.

When you get around to hitting the "accept" key, remember that feedback is always greatly appreciated as is any bonus's and remember, that doesn't preclude and further help. Good luck, Dave

The Small Engine Doctor and 3 other Small Engine Specialists are ready to help you
Customer: replied 9 years ago.
Hey Dave, it still won't start! I'm tearing my hair out here. I just replaced the carburetor and coil, and have good blue spark and fuel getting to it. The engine cranks fine then lurches 2 or 3 times like it's trying to catch and backfires. I've checked the flywheel key to be sure it wasn't sheared and throwing off the timing. I've also checked the push rods to be sure they aren't bent. The compression is around 85 lbs. Any thoughts?
Hi Gary, Trust me, I'll be tearing along with you because I'm "invested" also. I just picked this post up because I wanted to give a quick check before leaving. I've got to go out for about an hour or two and while I'm driving, I'll give it some thought and I'm sure when I get back I'll have something. Speak to you soon, Dave
Customer: replied 9 years ago.
Ok, thanks
Sorry Gary, I got caught up in some important stuff. I,ll try to give this matter some attention today. Thanks for being patient, Dave
OK, I had to review what we did before. You say you replaced the carb and coil. When you replaced the coil. did you "gap" it properly to the flywheel? Second, and bear with me, what kind, and what number spark plug are we using? Whenever you get back to me is fine. I'll try to stay with this as best I can
Customer: replied 9 years ago.
I gapped the coil to the flywheel using a very thin piece of cardboard... about the thjickness of 2 business cards. There wasn't much play to adjust, so I just made sure both sides of the coil were evenly spaced from the flywheel. The spark plug is a Champion RC12YC, and I've tried 4 different plugs with that number gapped to 40.
I just cut a business card in half to see what "size" it is. .020", perfect!!!Of course I don't know if my cards are the same as your cards but.........Heres what could be happening, especially with reference to the lurching. The engine is equipped with a compression release mechanism, as are most engines. This gizmo resides on the camshaft and holds one of the valves open just slightly during the compression stroke to relieve some compression because the starter (but mainly everyones wrist) doesn't have the power to compress ALL of the stroke. I don't know if you've ever experienced a backfire while trying to pull start a small engine. If you did, you wouldn't forget it to soon. If not, I hope you never do. Al any rate, it is possible your engine goes around one or two revolutions and then the "thing" releases and Bang!!! The problem is that its impossible to tell for sure if this is EXACTLY whats happening. Another thing that could compound the situation is that you may see a plug fire well outside of the engine, but when you put it in, the extra high compression could blow it out, just like a candle!! One more thing is that your engine has hydraulic lifters, so you can't "mess around" with the valve adjustment. I'm going to look into some things but in the mean time, take out the Champion and see if you can find an equivalent NGK and gap it to .030" and see what happens. I'll be back ASAP, Dave
Customer: replied 9 years ago.
Ok, I'll try to find an NGK plug after work tomorrow.
Customer: replied 9 years ago.
Hi Dave! I replaced the Champion plug with an NGK equivalent. Still won't start, but it backfires better than ever! Could the seat switch possibly be bad? Seems like it shouldn't even crank if you're not on the seat but it does, as long as the brake pedal is depressed. At any rate, it won't start whether you're on the seat or not.