Export thread

Hello, hoping someone here can help- I'm going crazy! I bought a tiger cub with Kawasaki 19 HP moto new 3 years ago. I have less then 200 hours on motor and mower. This mower is only used on my property of less then 5 acres.
On occasion when I cut the grass the motor idle will jump up and down. Sometimes I can go for 3 hours without any problem then suddenly motor idle will get eratic. It can happen without the cutting deck engaged and just idleing or while I am cutting. If it does it when I'm cutting the motor will die. It's been back to the dealer twice for this problem with no luck. Help, I'd like to get thru this season without this problem. On the positive side the mower itself is a tank.
Model: Scag Tiger Cub STC48V- 19KAI

I'm a retired mechanic but in addition to limited commercial mowing I do maintenance on machines for a select group of customers. Trouble shooting is an acquired art and difficult to do on line but I will give you some possibilities. All modern power equipment engines that have electric start and a charging system have a fuel shutoff solenoid in the carburetor and this is required by mandatory safety standards. Modern engines have ignition systems that do not need a power source to produce spark, just cranking the engine provides the spark at the right time for ignition. However the rest of the machine is electrically dependant and the control of this electricity starts at the key switch and into the electrical system that includes many safety circuits. The fuel shutoff solenoid is part of the electrical system that needs power to keep it open during operation and can be problematic along with the keyswitch itself. The keyswitch has many functions; grounding the ignition system to shut down the engine, disconnecting the charging system to prevent backfeeding, and removing the battery power from all systems connected to it when in the off position. When in the on position, the reverse of all of the above happens, so a properly functioning keyswitch is important. There are many switches and relays in the safety circuits some of which directly affect engine operation.
Operators that use a water hose to clean their machines have more electrical problems than those who clean their machines with HP air. Other possible trouble areas are fuses and fuse holders, engine and frame grounding points, chaffed wires, corroded plug in connections, in addition to all the switches in the safety circuits. One needs to have a machine specific wiring diagram, a knowledge of electricity, and electrical test equipment in order to trouble shoot machines. Then there is a fuel system, where filters, hoses, tank venting, shutoff valves, and fuel pumps are involved!!!
If your machine shuts down during operation then you have more than an engine idling problem.
Mad Mackie in CT:biggrin::laughing:

I have the same issue on the same mower! I believe I have it narrowed down to the Solenoid on the carburetor. The reason I say that is because when the motor starts to shut down I will turn the key on just before the starter engages and it will start running again. Its almost like it is powering the solenoid again. when the motor quits I can hear the solenoid kick back in and then it will start again.
My question is this, is it a bad solenoid or is the signal to the solenoid kicking in at the wrong time. Where does the signal come from? What tells it to activate and turn the gas off. I have cleaned the carb many times and checked the solenoid and it seems to activate when power is put to it.
Can you bypass this so it wont be an issue? This is a great mower but is very frustrating. I went through the complete fuel system from tanks to card and everything is good on that end. I sure hope you can help me out Mad Mackie it sounds like you are very knowledgable on these motors and I would greatly appreciate your help.............PLEASE!

As best that I can see from wiring diagrams is that the power that goes to the fuel shut off solenoid comes directly from the keyswitch, to the engine harness connector, to the fuel shutoff solenoid connector. Keyswitches are known to be problematic. The other problems that I have found is dirty and or corroded plugin connectors. There are many of these type connectors in the electrical systems on Scag and other makes of machines and they all are susceptable. The plugin connector on my Tiger Cub at the control module gets fine dust in it and I need to clean it often. The Scag wiring diagrams are difficult to read and with a different engine harness for each make of engine that are not in the diagram makes them more difficult to trace. From the keyswitch to the fuel shutoff solenoid there are at least three connectors and possibly more. I would also check the voltage at the battery to determine if the charging system is operating correctly. Run the engine at 1/2 throttle or higher and the voltage across the battery should be 13.8-14.3 volts DC.
In the past year I have had to clean every connector on two older ZTRs that I have serviced for electrical problems and had to replace the keyswitch on one.
Mad Mackie in CT

Thank you so much Mad Mackie, I will trace from the switch to the solenoid tomorrow. Would you happen to know if the voltage to the solenoid is 12v?
I just read on another forum that a guy actually replaced the solenoid with a screw, will this cause a problem with the fuel continuing to flow after the motor has stopped?

Yes it is a 12 volt solenoid, a single wire to it as it grounds thru the engine. You can replace the solenoid with a bolt and gasket and I have done this to several machines over the years. Make sure that the threads on the bolt are the same as the solenoid, they may be metric, you don't want to mess up the carb.
Mad Mackie in CT

Thanks again, I am going to try that trick with the screw first to see if it takes care of the problem. If not then go to the switch next. I will keep you posted :smile:

Periodically my Tiger Cub/26 Briggs if sits unused for several weeks in season will develop an irregular idling and running problem even with the use of StaBil. So I started using Sea Foam and it clears up the problem. Now with every refill of my gasoline storage jugs I use some Sea Foam, Star Tron, and ValvTect Carbon Free. I waited until some of my power equipment dealer frends experimented with " snake oils" and decided which ones were beneficial and I took their recommendations.
Since ethanol has become a regular thing in the gasoline here in CT, the red StaBil has become ineffective. StaBil now makes a blue colored product that is supposed to deal with the ethanol, but I probably will not use it as I'm pleased with Sea Foam, Star Tron, and ValvTect Carbon Free. However the use of these additives turns $4.40/gallon gasoline into $5.50/gallon gasoline!!!! :frown:
Mad Mackie in CT:biggrin::laughing:

Thats some great information and I thank you for it. Here in Michigan it is the same with the ethanol issues, since I am just a homeowner and really wont be putting that many hours on my machine I will be needing to do the same with the sea foam.

I do believe I figured out my issue with the motor stalling and I am "almost 100" sure it is the switch. I ended up bypassing the switch with a wire from the battery to the fuel solenoid and runs like a new machine again:smile:. I ordered the switch and it should be here this week to be sure. This was a frustrating ordeal for me because i never dreamt to look at the switch, I went completely through the fuel system to no avail. I didnt realize how much of the systems run through that switch. I thank you again Mad Mackie for helping me with this, I would still be looking.:confused2:

I forgot to add that I couldnt bypass the solenoid with a plug because they started putting a needle valve in the end of it to stop people from doing that. I guess the older machines you can still do that to.

Well I'm new to this site and found it by Googling Kawasaki idle issues. I have the 19 HP Kawasaki motor on my 48" Scag and it just developed a problem idling, so thanks to the information provided so far on this topic I will do some trouble shooting and hopefully resolve this issue. I will be back to let you know what I find. I have over 600 hours on this 2007 model mower as I mow over 4 acres. Thanks to all that have contributed to this site.

Have to agree about the benefits of using Seafoam* It has been around since about 1942, my Dad used it & swore by it..

It will also stabilize fuel for 2 years, & the container has no expiration on shelf life..

Seafoam has even worked on one of my air-guns that got gummed up.. Good Stuff.. I don't use it thru the year, because we can still get 100% gas here, but this time of year, I start using it, so when I do my last mow, my machines are ready & can safely sleep till spring..


Sta-Bil however does have an expiration on it. Once opened, you should not use the contents after 2 years. (Believe me). Says it in the fine print on the bottle.

TexasM said:

Well I'm new to this site and found it by Googling Kawasaki idle issues. I have the 19 HP Kawasaki motor on my 48" Scag and it just developed a problem idling, so thanks to the information provided so far on this topic I will do some trouble shooting and hopefully resolve this issue. I will be back to let you know what I find. I have over 600 hours on this 2007 model mower as I mow over 4 acres. Thanks to all that have contributed to this site.

Click to expand...

I removed filter assembly and loosened carb, also removed float bowl, blew air through jets in throttle body and gas inlet line In doing so, something popped off top of carb. exposing what appears to be a jet. since I couldn't find this piece I trimmed a rubber pencil eraser and plugged the small hole then sealed this with rubber type gasket sealer.
After reassembling everything, with some difficulty getting float bowl gasket to seal, I restarted mower and it idled fine, so apparently there was some trash in one of the jets. Talking with mechanic at local dealer he said there is low, intermediate and high speed jets in carb. Anyway, not as easy as I thought to do this job and bolts are metric not US standard, but have it running again.

7394 said:

Have to agree about the benefits of using Seafoam* It has been around since about 1942, my Dad used it & swore by it..

It will also stabilize fuel for 2 years, & the container has no expiration on shelf life..

Seafoam has even worked on one of my air-guns that got gummed up.. Good Stuff.. I don't use it thru the year, because we can still get 100% gas here, but this time of year, I start using it, so when I do my last mow, my machines are ready & can safely sleep till spring..


Sta-Bil however does have an expiration on it. Once opened, you should not use the contents after 2 years. (Believe me). Says it in the fine print on the bottle.

Click to expand...

Thanks for the info. I bought a can of Seafoam and added to my gas tank and spare gas cans, so will see how it performs. Thanks.