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Mower Engine Diagnosis Help #5461720 06/24/20 07:00 PM
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doitmyself Offline OP
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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.

Re: Mower Engine Diagnosis Help [Re: doitmyself] #5461729 06/24/20 07:12 PM
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Chris142 Offline
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Carb main jet is restricted. Closing the choke richens the mixture enough to allow it to run better.


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Re: Mower Engine Diagnosis Help [Re: doitmyself] #5461745 06/24/20 07:32 PM
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irad Offline
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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.

Re: Mower Engine Diagnosis Help [Re: doitmyself] #5461746 06/24/20 07:35 PM
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spasm3 Online Happy
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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 by spasm3; 06/24/20 07:35 PM.

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Re: Mower Engine Diagnosis Help [Re: doitmyself] #5461773 06/24/20 08:15 PM
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Dinoburner Offline
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Sounds like a fuel problem from here but a compression test might be called for.


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Re: Mower Engine Diagnosis Help [Re: doitmyself] #5461792 06/24/20 08:50 PM
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doitmyself Offline OP
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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/

Re: Mower Engine Diagnosis Help [Re: Chris142] #5461911 06/24/20 11:29 PM
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Linctex Offline
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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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Re: Mower Engine Diagnosis Help [Re: doitmyself] #5462058 06/25/20 06:58 AM
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mk378 Offline
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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.

Re: Mower Engine Diagnosis Help [Re: irad] #5462063 06/25/20 07:14 AM
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wag123 Online Content
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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).

Re: Mower Engine Diagnosis Help [Re: wag123] #5462117 06/25/20 08:28 AM
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jeepman3071 Online Content
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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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Re: Mower Engine Diagnosis Help [Re: doitmyself] #5462513 06/25/20 03:29 PM
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Duffyjr Offline
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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.


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Re: Mower Engine Diagnosis Help [Re: doitmyself] #5462555 06/25/20 04:02 PM
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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 .


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Re: Mower Engine Diagnosis Help [Re: doitmyself] #5462711 06/25/20 06:26 PM
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doitmyself Offline OP
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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?


Re: Mower Engine Diagnosis Help [Re: doitmyself] #5462777 06/25/20 07:49 PM
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JTK Offline
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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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Re: Mower Engine Diagnosis Help [Re: doitmyself] #5463039 06/26/20 06:54 AM
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wag123 Online Content
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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.

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