25 hp kawasaki won't run full throttle after warmup.

[stillyoungenuff]

Hello. I'm new to this forum and new to Kawasaki engines. I need some guidance on a RPM problem with a 25 HP Kawasaki. I bought a new zero turn 52 inch cut Gravely for my grandson to start a lawn mowing business. It only has 102 hours on it but after he mows a yard and shuts it off for awhile to do the trimming it doesn't run right for awhile. It seems to not come up to full throttle and doesn't have the power it should have when he moves to the next yard. Sometimes it will snap out of it after a few minutes but sometimes not for 30 or 40 minutes. Yesterday it never did get right and he had to finish mowing much slower because of lack of power. I changed the fuel filter this morning and it ran good for one yard but then started acting up after he was done trimming. We have taken it back to the dealer as it was under warranty but they say nothing is wrong. My guess is they don't run it long enough before shutting it off to notice the problem. Does anybody on here have any suggestions where the problem may be. I'm suspicioning an issue with the fuel system but would sure appreciate any input on this. Thank you much.

 

[bertsmobile1]

The symptoms fit a failed auto choke perfectly but AFAIK that engine does not have one, but we are a season or two behind the USA for model updates

 

[7394]

I don't believe Kawasaki's have auto choke either.. Not that IKO..

 

[stillyoungenuff]

This mower has a manual choke. I thought at first the motor was starving of fuel and tried pulling the choke out a little, maybe a fourth of full choke. It seemed at first the motor may have picked up a little but it sure didn't get back to full steam. I couldn't hold the choke in that position and control the steering lever at the same time so when I let go of the choke it slowly went back to open position. Thanks so much for responding back. I really need to figure this out for him. He is only fifteen and has to work pretty hard to keep his yards mowed. He needs that mower working at 100 percent. I will look into the choke again. The motor doesn't seem to act up until he shuts it off after mowing awhile then restarts it. Another thing I might add is about a week ago I took the fuel line off at the fuel pump and blew back through it thinking there may be something clogging the line in the tank. After doing this it ran good thru several yards before starting the same problem a couple days ago. I blew back through the line again and changed the fuel filter but the problem was still there later that day. I feel it is something simple but I'm stumped right now. Thank you for your reply.

 

[slomo]

a week ago I took the fuel line off at the fuel pump and blew back through it thinking there may be something clogging the line in the tank. After doing this it ran good thru several yards before starting the same problem a couple days ago.

You are on to something. Sounds like you have grass and junk in the tank slash fuel system.

Dump the fuel tank. Remove it if you have to. Get it like a newly purchased tank. Blow out with compressed air. Pull every line OFF and blow out. Test AT the carb into a glass jar. Crank the key a couple times. Should pulsate fuel into the clear canning jar. Summation, dump entire fuel system and add fresh non ethanol fuel.

Also be looking for water. I've found water even on mowers that are using 100% real gas these days. Some pumps do E-10 and real gas, same hose. I don't use those stations.

 

[hlw49]

Can you look into the tank and see the pick up tube? May be trash floating around in the tank and stopping up the fuel line. And when it is not running it quits pulling fuel and drops off. Had one not long ago doing this.

 

[stillyoungenuff]

I can't see into the tank as there is a dog leg type bend in the filler neck. I agree I need to remove the tank, clean and flush tank and lines. That is my next move. I wanted to check with you folks more knowledgeable than I before doing so. I didn't know if there could be something in the electrical system that quits when the motor warms up so I wanted your input. I will get back with you after the tank cleaning to let you know if that was the problem. Much obliged for the replies.

 

[bertsmobile1]

Debris can build up inside the tank but usually it happens the opposite way
While running the debris gets sucked into the outlet & plugs it off then floats away when the engine is off .
The easiest way to rule the supply in or out is to rig up an auxillary fuel tank and the instant it plays up. pull the original fuel line off and slip the auxilary on on.
It does not need to be big, a tank from an old push mower will do, old motorcycle just needs to be about one of you quarts
And of course you will need to block off the old fuel line.

It might just be a vacuum lock because the tank is not venting
So you can also try loosening the fuel cap about 1 turn when it plays up .
That model should have a vent line from the tank to the manifold on the engine side of the carb which can get pinched so the tank does not vent .

These sorts of problems can be a bugger to diagnose and the factory only allows an small amount of time to do the diagnosis
Then if it is found to be a non warranty repair they have to hit you up for 2 hours or more for the diagnosis + the repair .

 

[slomo]

Once the entire fuel system has been cleaned and flushed, I would look into your ignition coils. Check for strong spark when it starts to fizzle out on you.

New mower, I would look into the valves too. Maybe a rocker is loose or lash out of spec. Shot in the dark that isn't directly related to your issue. If the valves were out, would run strange all the time. Something is wrong obviously.

Air, fuel, spark and compression is what you need.

 

[stillyoungenuff]

Thank you lawn royalty and lawn addict. I did not think about the tank not venting but that needs checked for sure. I had a snapper with briggs motor that kept dying and that was the issue. I always believe in checking the easy thing first. I'll check that out and clean the tank and lines to start out with. My grandson hauls gas to the mower in jugs and one of the jugs could have had some debris and got into the tank. I don't know if the line in the tank has a screen over it but if so it probably wouldn't take much to partially close it off. The thing that throws me off a little is that it runs good until he shuts it off. He has three yards to mow today and I told him to mow all three before shutting it off and then go back and trim them. If it runs good on all three yards then I may be looking at something besides plugged fuel lines. First things first tho and checking the vent and cleaning the tank and lines seems to me to be the place to start. I'll get back on here with what I find out. A good forum has solved many problems for me and I feel this is a good one. Appreciate your suggestions. Stay safe.