Engine Exmark up to its old tricks, starts but lacks power, back fires and runs rough under

djacks44

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My Exmark Z with 60" deck and 25 horizontal shaft kohler starts hard. Seems to run OK once running until engaging mower then cuts out, misses and back fires. Thought I had it fixed when I located some electrical problems (fuel solenoid, 20 amp fuse socket dirty, not making good contact) finally gave up and took it to the local Exmark dealer, they called today scratching their heads. Seems it only runs on one cylinder but spark test shows good spark to both when it runs rough and backfires. These guys have been in business more than 25 years and I have confidence in them but can't explain this. The hour meter shows 1400+ but it may have been replaced as the unit is a 1998. The tech said compression looked ok. He said he checked all the normal stuff be he is baffled too. HELP!!!
 

Dnapropman

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My Exmark Z with 60" deck and 25 horizontal shaft kohler starts hard. Seems to run OK once running until engaging mower then cuts out, misses and back fires. Thought I had it fixed when I located some electrical problems (fuel solenoid, 20 amp fuse socket dirty, not making good contact) finally gave up and took it to the local Exmark dealer, they called today scratching their heads. Seems it only runs on one cylinder but spark test shows good spark to both when it runs rough and backfires. These guys have been in business more than 25 years and I have confidence in them but can't explain this. The hour meter shows 1400+ but it may have been replaced as the unit is a 1998. The tech said compression looked ok. He said he checked all the normal stuff be he is baffled too. HELP!!!
I am having similar problems please let me know when your solution ends up being
 

Rivets

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Running on one cylinder is normally caused by one of three things. No spark to that cylinder, no fuel in that cylinder or blown head gasket on that cylinder. Here’s how I would proceed. First check for spark. Second, check to see if the valves are opening and closing properly. Third, check valve clearance. If all three of these checks are positive and the cylinder still has no power, I would then be pulling the head and replacing the head gasket. Others have different checks, but this is where I start.
 

bertsmobile1

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While the shop may have been around for a long time do you know which tech looked at your mower ?
So I start with the visual / mechanical , timimg key intact, valve lash correct, choke firm , etc, hen go on to field testing.
My first field test in these case is always to check that the carb solenoid works then disconnect the both kill wires from the coils and go mow, carefully
Problem goes away = mower electrical problem
Next test is to mow again, but take a substitute fuel tank with me.
When it plays up I plug the alternative tank directly to the carb
Problem goes away = fuel supply problem

I can do this cause there is 1000 acres behind the shop and some of it always needs to be mowed except in droughts & bushfires soit costs me nothing to spend 2 hours testing a customers mower, UNDER LOAD .

A normal workshop can not do this, the best most can do is put some high lift blades on then shove it in a corner of the shop / carpark and leave it running while the closest tech glances across at it from time to time .
Occasional problems are a headache for workshops cause if you got a bill that had $ 600 for "testing , diagnosis & evaluation " you would hit the roof but that is the sort off cost big workshops face in cases like yours .
 

Born2Mow

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1. "Cranks but won't pull a load" sounds like the jets are not flowing enough fuel. When ethanol fuels are allowed to sit in the float bowl, they eventually cause a "varnish" to coat the inside of the carb. Mower carb jets are so small and fuel metering so precise that even a thin varnish is enough to choke off needed fuel. The engine lacks fuel, thus the engine lacks power. Pull the float bowl and look for a green or brown coating.

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2. Modern ethanol fuel goes bad in 8-10 weeks. As the alcohol separates from the gasoline, power starts to seriously decrease. Replace the fuel.
 

Hammermechanicman

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2. Modern ethanol fuel goes bad in 8-10 weeks. As the alcohol separates from the gasoline, power starts to seriously decrease. Replace the fuel.

Since i run a small mower shop i think ethanol in gas is the best thing since sliced bread. i keep 30-40 gallons of regular gas on hand at most times in sealed 5 gal cans. I have had gas sit in cans for the better part of a year and had no issues using the fuel in any of my equipment. Amazingly enough my old motor home sat for 5+ years in the barn with half a tank of gas and it started and ran fine this summer. Ethanol gas sucks but if kept in a sealed container it will last quite a long time. Just not in a carburetor.
 

Born2Mow

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My Exmark Z with 60" deck and 25 horizontal shaft Kohler starts hard. Seems to run OK once running until engaging mower then cuts out, misses and back fires. Thought I had it fixed when I located some electrical problems (fuel solenoid, 20 amp fuse socket dirty, not making good contact) finally gave up...
If cleaning the fuse socket helped once, you may have micro-corrosion throughout on all the electrical connectors. A simple, but highly effective way to treat this is to unplug each electrical connector (including fuses and relays) and apply a tiny amount of anti-oxidation compound. Such a product is No-Ox-Id by Sanchem. Their smallest container is enough to treat 20 mowers and motorcycles.

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Seems it only runs on one cylinder but spark test shows good spark to both when it runs rough and backfires. These guys have been in business more than 25 years and I have confidence in them but can't explain this. The hour meter shows 1400+ but it may have been replaced as the unit is a 1998. The tech said compression looked ok. He said he checked all the normal stuff be he is baffled too. HELP!!!
Therein may lie the issue. So much of yesterday's knowledge no longer applies to modern engines. One such area is ignitions, which have changed over from magneto and battery-coil, to solid-state triggers. The newer transistorized ignitions can be defeated by magnetic fields, poor electrical connections, low battery voltage, temperature extremes.... things you can't see. It's an entirely NEW way you have to think, in order to diagnose.

Another area is "grounding". It used to be accepted to use the frame and/or engine as an electrical path (IOW to save on the cost of wiring). When an electric lamp (headlamp for instance) looses "ground" it's very easy to see and therefore detect. But when the same thing happens to your ignition module or electric clutches, it's not so easy. Your engine still requires a "ground" connection, but your ignition module may need the addition of a copper wire added to make the electrical return connection it requires.

Hope this helps.
 
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