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Ok, I am stumped. I have a Z 915 B that I purchased new a few years ago. This past weekend, I fired up the mower for the first use of the season and mowed for about 4 hours without issue. When I was done for the day, I washed the mower with a garden hose and then put it back in my garage. The next day I went to use the mower and noticed that the engine would not run at full speed. After messing with the throttle for a bit, the motor finally ran at full speed like it was supposed to and I proceeded to mow again for about an hour. Later that day, I went to put the mower away and noticed that the motor would start and idle without issue, but would only get to about half to 3/4 speed.

It starts fine, idles great, but when you give it full throttle, it only revs to about half to 3/4 speed. If the deck is running, the blade speed is way down and the mower will stall if you try to cut any grass.

If the deck is not running and you drive around, the motor will almost stall out if you give it full forward input. Forget about trying to go up any hills.

If the mower is running and the throttle is set to wide open, I can manipulate the linkage and get the engine to rev like it should, however the governor will throttle it back.

The throttle cable has plenty of range, so that does not appear to be the problem.

I checked and cleaned the air filters, put a new fuel filter on it, and I also cleaned the spark plugs, but the engine will not run at full speed. I am kind of stumped on this one so I was wondering if there was anything else I should check?
 

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Sounds like a spring came off the governor or something along those lines.

Check your plugs too. Perhaps one is fouling up?

Last thing to check is the gas. Make sure it doesn’t have any water in it.
 

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You should realize the cause when you can wiggle or play with the carburetor linkage and it runs the full RPMs once again.

Oh well!, can't believe what a little water can do to cause major troubles. So, you sprayed water back there where all the carburetor linkage is located and it got all mixed up with the dirt, dust, and all the other grime that is collect there. The water/washing didn't loosing any nuts or bolts to cause the problem(s).

So, here's the solution to start. Remove the rear back panel...probably four bolts would do it, and thoroughly wash, clean all the linkage and governor parts.

Water ang gas don't mix very well, but, it will run ..sputter very madly a few minutes until it's had ran through the combustion system.
 

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Ok, I am stumped. I have a Z 915 B that I purchased new a few years ago. This past weekend, I fired up the mower for the first use of the season and mowed for about 4 hours without issue. When I was done for the day, I washed the mower with a garden hose and then put it back in my garage. The next day I went to use the mower and noticed that the engine would not run at full speed. After messing with the throttle for a bit, the motor finally ran at full speed like it was supposed to and I proceeded to mow again for about an hour. Later that day, I went to put the mower away and noticed that the motor would start and idle without issue, but would only get to about half to 3/4 speed.

It starts fine, idles great, but when you give it full throttle, it only revs to about half to 3/4 speed. If the deck is running, the blade speed is way down and the mower will stall if you try to cut any grass.

If the deck is not running and you drive around, the motor will almost stall out if you give it full forward input. Forget about trying to go up any hills.

If the mower is running and the throttle is set to wide open, I can manipulate the linkage and get the engine to rev like it should, however the governor will throttle it back.

The throttle cable has plenty of range, so that does not appear to be the problem.

I checked and cleaned the air filters, put a new fuel filter on it, and I also cleaned the spark plugs, but the engine will not run at full speed. I am kind of stumped on this one so I was wondering if there was anything else I should check?
I'd replace the plugs and maybe run some Sea Foam in the gas.
 

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Discussion Starter #5
She's back!

First off, thank you for your suggestions. After spending way too much time thinking about this, I faked my own death to get out of work early so I could come home and wrench on the mower. I took the back panel off and checked the springs to make sure they were all there, and that checked out ok. This mower is pretty clean, so the linkage looked good and there was no biding that I could see.

I checked the fuel and breather line for blockages and those checked out fine as well. I then decided to take the gas tank off and drain it. That was fun since it was pretty full. I captured most of the gas from the tank, however we may not have as many tulips come up as we have had in the past in one area of our yard. Once the tank was drained, I put it back together, dumped a can on Sea Foam in the tank, and then filled it with some fresh non ethanol gas.

I fired up the mower and it ran great. Drove around the yard and did some victory laps and did some test cutting to make sure everything worked. Runs like a champ now. So glad I didnt have to take it to the dealer. That said, I cannot for the life of me figure out how I got bad gas. My guess is that i somehow got water in the gas when I washed it, however I have never had this issue before. Moving forward, I think I will be a little more careful when cleaning it off.

Dano-
 

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You may have got some water in a plug wire while washing and it was only firing on one cylinder. Or.. You have a coil that is intermediately breaking down. This is a common issue with this model. I see on average 2 or 3 a month. Coils need to be replaced as a pair. In fact the repair kit comes with 2 coils and a wiring harness.
I have seen a coil stop firing then come back and run fine then fail again and on and on. Sooner or later it will fail for good.

Sent from my LGL52VL using Tapatalk
 
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