Do you have a coil problem? On this site restrob has the procedure to check coils. I don't have the link but I think you can find it...

 

Is it backfiring through the muffler or carb?
I'm thinking it might be a valve sticking on you
check the valve clearance ( its a quick check to do)

 

Also a sticky float needle could cause this along with a leaky head gasket, I'd check the float needle and leaning toward a sticky valve or valve clearance adjustment. If it was running fine before with only 350 hrs on it.

 

Is it backfiring through the muffler or carb?
I'm thinking it might be a valve sticking on you
check the valve clearance ( its a quick check to do)

It's backfiring through muffler. Just hought I'd add the last time this happend (the last time I used the mower before this episode now), I emptied the fuel tanks and filled up with high test fuel, and it didn't backfire. This time, it made no difference.

 

I'd do a quick check on the float needle and then valve clearance,...muffler backfiring could be either of them.

 

Put in 5 gallons with Chevron Techron carb cleaning concentrate fuel additive. Ran at idle today for like 2 hours. Then tried it out. It ran at full throttle with blades engaged but not cutting grass (on a drive way back and forth) just fine. Then I put it to cut grass, and after a few seconds of cutting (more load) and it then first slows down a bit just before commencing to backfire. I figured out that if I throttle back a tad from full speed at that point , it stops backfiring and then works without backfiring, however, I have to mow slower than I'm use to.

Does this change anything in any of your recomendations?

 

I'm leaning toward checking the valve clearance, since new fuel really didnt help much once you put the load on it,...looks like an exhaust valve might be sticking on you,...
Did you take the carb off and blow out all the jets~? ( if not I would do that also)

 

I'm leaning toward checking the valve clearance, since new fuel really didn't help much once you put the load on it,...looks like an exhaust valve might be sticking on you,...
Did you take the carb off and blow out all the jets~? ( if not I would do that also)

Looks like I got away cheap, continuing running the Chevron Techron Concentrate Fuel System Cleaner (1oz. per gallon of fuel)
at idle today for like two hours, and reving it up every so often to clean out carbon from the excessive idling, I got it back to working normal. I think it was carburetor related. Maybe having the float sit overnight in that concentrate fuel mix loosened it up? I've bunned about 2.5 gallons with the Techron through it. A motorcycle site on-line said it must be run at idle to clean the jets, as high speed does not work the jets (?), whatever, it worked. I mowed for like 20 minutes with no backfiring. Will run the rest of the Fuel/concentrate mix in the tanks tomorrow, 2 gallons, and refill with fuel only.

 

Good to hear~!
Some of us don't get away that cheap...
Happy Cutting~!

 

I don't use the mower much, like once a month, and a Toro dealer told me that fuel with ethanol (down here all gas station fuel contains maximum 10% ethanol) can loose like 10 octane in one month, and even worse as more time passes. Therefore, I additionally drained the tanks and filled with no ethanol 89 octane (from a boat marina), and the mower now runs beautifully.

I think the biggest culprit was the 10% ethanol fuel being well over 4 months old.

 

PM, ... good information on a remedy. Thanks for the follow up.

 

The mower went back to it's old tricks, and started dieing out when under the load of the mower deck. It would just loose power and trun off, and spit and backfire just before shutting down. I went through a lot of analyzing and work, and finally got it fixed today. It was the carburetor, it had a main jet plugged up and only working at about 20%. I took the carb apart and cleaned every jet, and orifice, and set the pilot screws at 1/4 turn out more than factory spec, ALL thanks to the detailed instructions of Lawnsite's Restrorob.

Thanks Restrorob!

I will start a new thread to detail all that went on to get it fixed. It will be titled "Kawasaki FD750D dies out only under Load". For those interested there is also some of what transpired day by day with my case, detailed on another thread of a person on Lawnsite, Mike FarmKid2 , that had the same problem, which to date he has not solved. That thread is titled " Kawasaki FD661D Loses Power".

 

Your very welcome Peter,

"I love it when a plan comes together" ! :clapping:

 

First I would like to say thanks for all of the information everyone provided on this site. I was having the same problem described in this and other threads. I was about to start removing the carburetor today for a good cleaning/replacement, but I read some of you choked the engine to keep it running. I was just shutting off the PTO (Gravely PM260Z) to keep it running. This problem looked like a real nightmare and had me thinking just buy a new motor and call it a day. However, I just tried the choking method of keeping it running to see if I had a similar result. My mower did not need to warm up to start with the problems. I went through a series of PTO on and off and choking on and off at different amounts to get the RPMs up as high as I could. At one point the engine stumbled and backfired and then the RPMs were where they should be. Apparently, choking the motor help clear whatever was blocking my high idle circuit. I did notice when the sudden onset of this problem occurred my fuel filter was cracked and covered with grime that stopped it from noticeably leaking. My theory is a small bit of crud made its way into the bowl. This forum is very helpful, but it can definitely scare the heck out of you with the potential problems you may have. Bad carb, burnt valve, bad PTO etc. Looks like I lucked out. One question: My FD750D does not have the model sticker or plate on it anywhere. I think it should have been on the fan shroud, but I checked every inch of the motor when I was thinking I needed a new carb. Of course there are two different carbs depending on your model. Is there any way to find out which model FD750D I have? I didn't even see a number stamped on the block anywhere. Thanks for all of the good info everyone.

 

Contact Gravely: https://support.gravely.com/manuals/#
They can prolly tell ya what motor was installed in yer unit.