Scag mower suddenly will only run at 40% throttle and 60% choke

If taking off the brake kills the motor, you need to check all the safety switches and wiring. Just because the seat switch has continuity doesn't mean it can't be the problem. Unplug the wires at the switches and examine the surfaces, you should see shiny where the contacts make contact. Jiggle wires, examine for damaged insulation etc. You said you used an inline spark tester, was it the light bulb type? They can five a false positive and make you think you have spark when you don't. A gap type tester is a much better test. If you can't do that, use a spark plug connected and grounded so you can see it spark. Get in the shade. You've got some spark anyhow, and some fuel. I wonder about that solenoid. How did you test it? You said tested on bench, did you just apply voltage and confirm movement? The connections to the solenoid can loosen and fail.
 
kawamoto26 said:
My old Turf Tiger with Kawasaki FD750 27hp has suddenly started having a problem starting. It starts under full choke with throttle turned up to about 30-40%. I immediately start decreasing the choke and it dies. Start it again and again and it runs for a few seconds and then dies. Eventually I can get it to run for 30-45 sec at 30% throttle and 60-80% choke. Move either the choke or the throttle and it dies immediately. Have gone through the fuel system from top to bottom:
Changed fuel filter
Cleaned carb twice and then put on a new one.
Confirmed fuel solenoid is working properly.
Replaced spark plugs.
Confirmed air filter is in good condition.
Confirmed fuel pump is pumping well.
Drained the gas and replaced with fresh.

Everything has checked out in good shape and I'm at my wits end trying to solve this while my grass is getting taller by the day. I only use ethanol free gas with Seafoam. Fuel system is spotless and now with many new parts.

Also, When I can get the engine running under 40% throttle and about 60% choke, it will die immediately if I take off the parking brake to try to move it. Not sure if that means something or if it is just too underpowered in that choked state. So, I'm currently do the diagnostics in my backyard because I can't even drive it to a trailer to take it in for service. Any help will be greatly appreciated.
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Hook up a nurse fuel tank temporarily (separate from one on the mower). Check intake gaskets to be sure they are good and not leaking. Correctly clean the OEM carburetor and reinstall. Having to manipulate the choke to keep engine running means you have a fuel to air mixture issue. Does the engine hunt and surge if you can keep it running?
 
New update: confirmed spark plugs are working by taking them out and watching for spark on both plugs. Both are firing just fine. Next confirmed 12V being delivered to the fuel pump. After a suggestion from my father-in-law, I checked the voltage across the battery and found it at 13.5v before starting. After starting the mower and running on 80% choke the voltage across the battery was 5-7V. Does this mean I have a bad voltage regulator? Could that mean I'm not getting 12V to the fuel solenoid? The wire on the solenoid is difficult to get to without removing the entire carburetor. I've also gone through batteries every 1-2 years, which would suggest the voltage regulator may have been frying them. Thoughts?
 
Sure sounds like a power problem. What is the voltage now? It sounds like the voltage went down with engine running, which sounds like alternator/regulator. Looking back where you said fuel flow drops off with engine turning over, which sounds like the same thing. Did you check the wiring? It sounds like a short in the ignition circuit, or a wire connected wrong.
 
I checked the wires to the fuel pump the wiring harness appears to be in decent shape. Haven't located the ground wire, but I'm not seeing any loose or damaged wires anywhere. Low voltage when the engine is running would definitely match with the symptom of seeing the fuel pump flow drop to a trickle.
 
Try blowing shop air back through the fuel supply line to see if it clears up the problem.

I have had lots of blocked fuel tank pickup tubes and fuel lines choke with grass chaff and garbage from dirty fuel cans.
 
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