John Deere LT160 won't rev up and rough running
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Thread: John Deere LT160 won't rev up and rough running

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    John Deere LT160 won't rev up and rough running

    Hi everyone I'm new here so please forgive me if I'm posting this thread in the wrong section. But I've recently bought a used lawn small ride on mower and up until recently I've had no issues. The machine has the 16hp Kohler engine fitted. I think it's original with only 300hrs on the meter.
    As soon as I purchased this mower I gave it a service using genuine parts, the usual oil filter, air/fuel filter and oil etc. After the service the mower ran ok and I continued to mow the lawn.
    My problems started the next time I mowed the lawn. (About 2wks later) The machine ran perfect for about an hour and then it started to loose power. I assumed it was running out of fuel so I limped it back to my shed for new fuel. But the fuel level was still ok in the tank. I started the engine and noticed that it wouldn't rev up. And that the idle speed was getting increasingly erratic. To the point that it was difficult to actually keep the engine running at all.
    I'm a mechanic by trade but I don't have any experience working on these small engines. My first thoughts were the fuel pump. I removed this and manually operated the arm and there was a suction. So I fit it back to the engine. But when the pump was installed back on the engine and at idle speed the suction was very poor. I'm not sure how much pressure these small pumps operate at. So I called my local John Deere shop and they advised me that they have never sold a fuel pump for this engine model, so it may be very unlikely that's at fault. I removed the air cleaner and squirted a small amount of fuel down the carb intake whilst the engine was running but the revs did not increase . It sounded like I'd flooded the engine. I wonder if I'd put too much fuel down. So I began then and pulled off the carb, I blew out the carb using compressed air, removed and checked the float etc. jets looked ok and not blocked. I checked the operation of the solenoid fuel shut off at the base of the carb. All seem ok. So I checked for a spark. I pulled off the HT lead and found a very weak erratic spark when cranking. I attempted to test the coil using my meter but only got resistance readings between the spark plug HT lead and the outer coil that bolts to the engine. I got nothing from the centre terminal and HT lead so I figure this coil to be at fault. I purchased a new genuine coil and fitted it to the engine.
    Still no better. So I looked further.
    I removed the valve cover to make sure the rockers where moving. The appear to be ok. I did notice I've only got 5 to 6 vdc coming from the coil terminal when running. Not sure if this is good. I know nothing about magneto coils. I assumed I should of put 12vdc to the coil from the ignition like car 4 stroke engines but when I tried this the engine stopped running. The engine also still ran no difference with this terminal wire disconnected. I'm guessing the coil makes it's own spark in connection with the flywheel pick up.
    Ive also checked the flywheel for looseness. It appears ok. I've also checked the coil/flywheel pick up is directly at piston TDC when opposite the coil. So I'm guessing the piston timing is ok. I've removed the new spark plug and refit the old one. Still no better. I did notice the spark plug is covered in black soot. This would lead me to believe a fuel issue. I removed the fuel pump once again and cranked the engine and I could see the cam lobe than pushes the fuel pump arm turning, so I'm assuming this is ok. I stripped down the fuel pump and the diaphragm is ok. I've also checked the fuel tank vent. That's ok.
    I'm
    Really at a loss as to what to try next. I know these engines are meant to be simple to maintain, I'm used to v8s. Lol. I think I've over looked something here. I might try a different batch of fuel and possibly replace the fuel lines and clamps. I have noticed that the spark from the new coil isn't much better than the old one. Anyone got any ideas on what to try next. I have noticed that when I moved my throttle lever to really low idle the engine then will idle very smoothly but when I go to increase the revs it just coughs and splutters and stalls. Also chuffed out black smoke from the exhaust. This once again would lead me to believe its fuel pressure related. Is there a way I can gravity feed the carb and bypass the fuel pump to test this theory? Any ideas or help would be greatly appreciated. Thanks.

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    For this symptom to show up suddenly, I would suspect fuel flow too. You did not mention if you tried blowing a low pressure air back through the line to the tank. I don't know exactly what the fuel pickup in the tank looks like. It may or may not have a screen in it. Part of it may be broken off and not able to draw fuel at the level it is now in the tank.
    If you want to gravity feed it for a test, I think you will want to detach the hose to the pump and plug it. Then make sure no residual fuel can spray out of the pump when you start the engine if you connect directly to the carb. Safety first! You can mount a small tank to a step ladder or something and run a new piece of fuel line from it to the carburetor or to the inlet of the fuel pump for test purposes. If it starts and runs well, you know where to go from there.

    The ignition coil is the electronic type. It has only the spark plug cable and a grounding post. The white (?) wire to that post only grounds the ignition coil to stop the engine. I have never checked for voltage there when the engine is running, but am sure that adding 12V to that post will damage the unit. If there is any voltage on that wire, check that out for shorting through the wiring harness and the switch. Could be a problem with the key switch.

    I may not be understanding your description of the timing of the flywheel magnet to TDC. The engine will spark with every revolution of the F/W just as the magnet meets or passes the legs of the coil. Of course only the spark just before TDC on the compression stroke is effective. If you are seeing TDC with the magnet 180 degrees from the coil, the flywheel key is sheared, I suspect. The only sure way to check the key is to pull the flywheel. If you do this be sure to torque the F/W nut properly when reinstalling it. The spark from this unit is usually thin and white. It looks weak but it will bite you pretty hard! LOL

    For more info on the engine go to www.kohlerplus.com. You can download a manual (free) for your engine model. Good luck to you and let us know how it goes. Ask more questions. We are here to help!

    tommyhawk

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    Take off the cap on the fuel tank and see how it runs. If the vent gets plugged with dirt, it will not run well above idle.

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    LT160 running rough

    Thankyou so much for your replies and advice. I crudely tested piston TDC by sticking a screw driver down the spark plug hole and rotated the flywheel until the screw driver was at its most sticking out stage! I noted the position of the coil pick up on the flywheel at this point and it was more or less opposite the coil. This I assumed was ok. The gravity feed procedure I'm going to try next. I will also check the fuel lines and pick up in the fuel tank. I tried running the engine with the fuel cap off and this made no difference. I was thinking last night maybe the engine is over fuelling and this is why it runs smooth at very low throttle opening. But I didn't find any issues when I removed the carb. Puzzling. Lol. It's a strange problem I'm having.
    I've also thought the key switch could be faulty, and I did actually take this apart too. The contacts inside where really dirty. I cleaned these and reassembled the switch but I'm suspecting it's faulty because sometimes you have to wriggle the key to get the hour meter and lights to work. It does need replacing but it looks simple in design and I'm thinking can this key switch be really causing this running rough issue? I understand what you are saying about the voltage at this coil white wire. Looking at the wire diagram the key switch puts this wire to earth and helps stop the engine. Should there be a small voltage there? At this point I'm really hoping this engine isn't stuffed, I've only had this mower a few weeks and I've spent lots of money refurbishing the deck with new spindles fresh paint etc. I'm determined to get to the bottom of this problem. Thankyou once again.

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    Update

    Well tonight I'd thought I'd look at my mower problem again. I've now removed/cleaned out the fuel tank and pick up and lines. Added fresh fuel.
    Removed and stripped down the fuel pump. Nothing visibly wrong with the diaphragm or rubber valves etc. working the pump manually does create a suction but it's pretty small. Maybe these small engines don't required lots of fuel pressure. Refit this back to the engine and when cranking it does seem to draw up fuel from the tank which can be visibly seen in the fuel filter. (Although the fuel only stays in the bottom of the filter)
    I removed the flywheel and double checked the key way for shearing off. All seems ok.
    I've checked once again the fuel shut off solenoid at the base of the carb. Plunges when key switch operated. Ok.
    Carb bowl full of fuel seems ok.
    There's just something I cannot get my head around. The engine won't really even start now and it sometimes back fires and has on a couple of occasions thrown flames from the carb inlet. (Filter removed) over fuelling ?
    These symptoms in my trade can indicate the ignition timing to be out causing the spark plugs to spark out of sync, but this is a single cylinder small engine. Im still not convinced my spark is strong enough at the spark plug, but the coil and spark plug are new (I hope I haven't blown this new coil by putting 12vdc to the kill terminal). Is there anyway the camshaft timing could be out even though the flyweel coil magnets line up when the piston is TDC? ? The camshaft is gear driven I understand? I haven't got around to bypassing the fuel pump as yet and testing the gravity method. That's tomorrow's job along with checking and rewiring this dodgy key switch.
    Why couldn't this fault of happened in winter when my lawn isn't a foot high!! Lol will keep you posted. I should possibly do a compression test but I'm scared at what I might find!!!

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    First I want to start over with a big "welcome to the forum"! I had not noticed you are in Australia. Do you have a long trip to a JD dealer or are you able to order parts through the internet?
    I have to admit that I thought you would find a sheared F/W key after all the normal things were checked out and cleaned. I don't know if there is a way to check that new coil for damage. I'll do some research on that. If you could unhook the white wire from the coil, attach your DC voltmeter to it and a good ground, turn on the keyswitch and take a reading. In my way of thinking, there should be NO voltage showing. Then turn the key to crank the engine a few turns. If there is any voltage present at either time, the keyswitch or wiring has a problem.
    You might want to reinstall the old coil and give it a go. If voltage is somehow getting to the coil they may both be shot. I need to look up more info on the engine model in your tractor. I have an older CV-14 Kohler that is similar the model you use, so I don't want to mislead you with wrong info. Not likely the camshaft is out of time, unless it somehow broke a tooth.

    Probably won't make you feel any better but we are heading into winter up here in the Midwest U.S. Mowing is mostly done, just leaves blowing every where!

    tommyhawk

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    LT160 headache

    Hi tommyhawk, thanks for your reply and advice. Yes I'm from the huge rock that's been baked in the sun for a million years!! It's coming into our summer here now so my garden is starting to look like a jungle.
    I live in Brisbane on the east coast I'm pretty lucky to have a JD dealer in the city. Most parts they stock but any special parts they can usually get them from Melbourne or direct from the states.
    Yes I was shocked to see that my flywheel key was still intact. I will check the voltage at this coil terminal tomorrow. I'm pretty sure when I last checked it there were approx 5vdc there. I'm also going to check out the wiring.
    I've read on the net other people have had horror stories with this model of JD. One story I read involved a snapped camshaft. Their engine would idle but not rev up.
    Another person had a warped carb heat shield gasket between the cyl head and carb. I'm going to check this too. I'm determined to get to the bottom of this issue. I'm just hoping the engine isn't stuffed. Lol

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    Hi Darran. I finally found the right Kohler service manual for the engine JD lists for your tractor, CV-460S. Kohler does not seem to recognize that model in the search page, but I finally located it by looking under CV-450/CV15. It is included with those models. Weird, huh?
    So all they tell about checking the coil is to measure resistance from the spark plug wire to a clean ground on the laminated frame or legs. A reading of 7,900 to 18,400 ohms is good. Higher or lower is bad. A typical wiring diagram they show only shows the wire from the stud as going to a switch to ground. So I still think any voltage on that wire is suspect.

    There is an older 16HP model, CV16, that has an electronic spark advance module. It would be located on the outside of the F/W cover. It has wires that go into the coil. Forgot to check if it uses a different coil, but probably does. It was a somewhat troublesome feature from what I've read, and should not be on your newer engine as best I can tell. I have no personal experience with that item. It is something for you to read about. Pretty cool even if it didn't work so well.

    I was also wondering if you have registered on www.jdparts.com? I believe this is world wide and would be quite valuable to you if it's available. It's free, you just have to register, list the name of your favorite dealer, and you can access nearly all the parts diagrams for JD equipment. Here, I can check the price of the part and my dealer's inventory right from home. If this is something new for you, ask your dealer about it. They sometimes have a free CD instructional guide to show how to use it.

    Just speculating on this but the camshaft is probably a one piece cast steel or cast iron part. Don't think they have used any plastic gears in the Command series. They don't usually break without a complete engine failure. There is a balance shaft also. This design is reliable. The old K series with balance gears, not so much. The old K series without balance gears were thumping, vibrating, reliable engines. In my opinion, the Command series is a very good one too.

    I have heard of the gasket and spacer problem between the carburetor and the block. Not common, but it would create a huge vacuum leak. We haven't discussed the possibility of a blown head gasket. If you try a normal compression test, the reading will be low due to the built in compression release. You may have the equipment to do a leak down test, though. That is a better test for these engines. A plugged exhaust is a remote possibility unless some of those "kangaroo mice" filled the muffler with something. LOL
    Hang in there! It will mow again soon.

    tommyhawk

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    LT160 continues to make my brain hurt!!

    Hi tommyhawk I like the 'kangaroo mice'. I've never come across the JD website you mentioned. I will check this out. Your correct my Kohler is the type with only one coil and a rectifier fixed to the outside of the flywheel cover. From memory I think I got around 13k ohms from the outer laminates to spark plug lead. I'm going to definitely check out my wiring and even replace the connections on the key switch. I've given myself a day off from the mower. Time to rethink and come up with some more tests I think. I haven't tested the compression. I know there is some due to the resistance when I turn the flywheel by hand but not sure how much. I think the camshaft is gear driven as you mentioned. I've not heard any strange noises from the engine prior to my fault or the brief time it runs afterwards, so I'm hoping the camshaft is intact. I'm going to remove the carb again and check out this gasket. But I would of thought if this gasket was warped my issue would of been more gradual and not literally one minute ok and the next not. I cannot believe this small simple Kohler engine is giving me so much grief, I'm used to dealing with much more complex engines with VVT,s etc these I can diagnose faults much easier! Lol. I cannot help thinking I've over looked something. I'm going to get back to the basics I think. Will keep you posted! Daz

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    Update

    I'm thinking more now that there's an internal fault with my camshaft or buckets etc. I've rewired the key switch. Working ok now.
    I've checked for zero volts at the coil kill wire.
    The engine will start up sometimes but idles very rough. And will only run for less than a minute or so before stalling in a puff of smoke from carb or backfire. Certainly won't increase rpm's without stalling.
    I have noticed that sometimes when it's stalling the flywheel rotates backwards! Not sure if this is normal?
    Any thoughts?
    I'm thinking of maybe letting my JD dealer have a look at it but could turn out to be costly.
    I've even thought about just getting another engine and replacing mine. But at only 300hrs on mine, surely it should of lasted longer than this.

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