Mower Engine Diagnosis Help

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Hello Gang, I have a sick engine on my workplace Exmark commercial zero turn mower. 12 years old with 900 hours. 23 hp Kawasaki FH680V 2 cylinder engine. Air and fuel filter good. Plugs are at 150 hours, look good - maybe should try replacement first? Fuel tanks venting o.k.. Lots of gas in the fuel filter - seems that fuel pump is o.k.? Excellent maintenance and fuel management (E10). I ran about two tanks of Techron infused gas with no improvement. Symptoms: Engine runs rough and seems to lack power. Occasionally pops/backfires when release the blade pto. Go over a BIG bump and occasionally can cough a bit, lose power. Key symptom: Runs better, about 85% o.k. when I have the choke lever at 50%. My hunch is either carburetor or maybe valves (never been adjusted)? Anyone have diagnostic procedure suggestions before I begin parts swapping? What symptoms would be tied to out of adjustment valves? FYI, the carburetor has fixed jets with only idle speed adjustment. Rebuild parts run about $130 (no kit). OEM replacement = $225+. Chinese replacement = $65. Not keen on Chinese carb on such an expensive machine. Thanks for any ideas. I'm pretty small engine savvy - have done rebuilds of entire engines and components. Hate to replace carb and not fix it.
 
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Here is a quick attempt to fix. Disconnect the fuel line at the carb. Attach a bike pump to the carb fuel nipple. Pump ten times and reconnect the fuel hose. Fixes the jets about 50% of the time.
 
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Probably what is stated above, usually running right with the choke out, is plugged jet or venturi. Before ordering parts, i'd just take it apart and clean it. Run a stylet in every jet and orifice. If the valves are adjustable, might be time for that too.
 
Last edited:

doitmyself

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Wow, thanks everyone. Dinoburner, knowing the 4 necessities of engine operation (fuel, spark, compression, timing) I, too, had compression on my mind. spasm3 - I've been procrastinating the valve adjustment because this thing has always run like a gem (I should know better). Intrigued by irad 's idea! Will probably order some gaskets first, then pull the carb off and see if I can clean it. Carb diagram if anyone is interested. A bit more complicated than others I've dealt with: https://www.partstree.com/models/fh680v-ds21-kawasaki-engine/carburetor-1/
 
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Originally Posted by Chris142
Carb main jet is restricted. Closing the choke richens the mixture enough to allow it to run better.
^^ 100%
 
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Two-barrel carb like that has a separate jet for each cylinder. So it's easy to end up running on one cylinder.
 
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Originally Posted by irad
Here is a quick attempt to fix. Disconnect the fuel line at the carb. Attach a bike pump to the carb fuel nipple. Pump ten times and reconnect the fuel hose. Fixes the jets about 50% of the time.
This won't work for cleaning the jets. The float bowl is vented. The only way to clean them is to take the carb apart and poke through the jets with a fine steel wire. I use the wire in twist ties (with the plastic removed).
 
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Originally Posted by wag123
Originally Posted by irad
Here is a quick attempt to fix. Disconnect the fuel line at the carb. Attach a bike pump to the carb fuel nipple. Pump ten times and reconnect the fuel hose. Fixes the jets about 50% of the time.
This won't work for cleaning the jets. The float bowl is vented. The only way to clean them is to take the carb apart and poke through the jets with a fine steel wire. I use the wire in twist ties (with the plastic removed).
+1 Twist tie wire or wires from a wire brush work really well.
 
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I think Techron is better suited for maintenance to keep things clean but not so good if your at the point of rough running. I would try some Star Tron before I'd tear in to the carb.
 

CT8

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Is there a carb. float bowl drain?? if so drain the float bowl out to see it there is some water then see how it runs .
 

doitmyself

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Thank you all. It looks like I will not be able to attack this until next week. I am leery to pull the carb without having replacement gaskets on hand in case they stick or tear. I have guitar strings that might make good jet cleaners and will utilize the good info above also. Having not worked on this carb before, will the two main jets be easily accessible - hard to tell from the schematic linked above? Following Duffyjr comment, are there stronger in tank cleaners that might dissolve any blockage? I'm guessing (completely) that some type of particle maybe lodged in one of the jets? CT8, it does have a float bowl drain screw. Will try this bowl drain first - very good idea. Beyond draining the bowl, what if I used some gentle air pressure and blew it into the drain hole?
 

JTK

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Didn't some older Kawi V-twins use a plastic cam that could wear and lead to similar issues?
 
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Originally Posted by doitmyself
Following Duffyjr comment, are there stronger in tank cleaners that might dissolve any blockage? I'm guessing (completely) that some type of particle maybe lodged in one of the jets?
Putting something in the fuel to open-up a plugged jet won't work. The jet has to be open for something to be able to flow through it. In your case, it is likely a piece of dirt/sand that is plugging the jet. No additive will dissolve this anyway.
Originally Posted by doitmyself
CT8, it does have a float bowl drain screw. Will try this bowl drain first - very good idea. Beyond draining the bowl, what if I used some gentle air pressure and blew it into the drain hole?
The float bowl is vented. Blowing air into it by any means won't open-up a plugged jet. No way around it, the carburetor is going to have to be disassembled and the jets manually cleaned. 95% of the time you won't need a carb kit or gaskets other than sometimes a carb to intake manifold gasket. The float bowl will have an o-ring or rubber gasket. Once you have poked through all of the jets, spray carb cleaner though all of them, and the idle circuits, to make sure they are clear. If you are not comfortable doing this yourself, take it to a shop and pay to have it done.
 

doitmyself

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Originally Posted by JTK
Didn't some older Kawi V-twins use a plastic cam that could wear and lead to similar issues?
I had one of those on my previous John Deere F725 with water cooled Kawasaki engine. When the water pump went out, a mechanic told me to go ahead and replace the plastic cam while the engine was apart because it would fail next. He told me that John Deere specified that plastic cam on their Kawasaki powered mowers as an attempt to quiet the engine down. Thanks wag123 for the info. I have had a number of carbs apart over the decades, just not one of these 2 barrel ones. I'm going to have to learn how to measure and maybe adjust the valves too. I hear you about the gaskets. If I try removal without any replacements on hand, I will at least make sure I can mail order them quick in case I have problems.
 
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Get some Berrymans Chem-Tool and pour a healthy dose, 1/4 cup or so, into the tank. Run the mower, it may clear out or it may take a week. I'm about 3 for 5 with it working. grin2
 
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