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We have a 5 year old Snapper rear bagger that has begun acting up lately. We bought it from a friend at the end of the 2014 mowing season and my son used it all summer and fall last year without any issues.

This year, my wife told me that it was getting hard to crank, especially when the engine was hot. This weekend, I was trying out my Husqvarna repair and had a problem after finishing the front lawn, so I went and grabbed the Snapper to finish up. It wouldn't crank and I checked the spark plug (which was replaced last fall), but it was heavily caked with carbon so I replaced it.

It cranked easily, but I cut one pass and the engine started racing. Pulling the throttle lever all the way to slow did not affect the idle speed, even though I saw the throttle moving. It began to smoke, so I stopped it immediately. It was getting too dark to work and my wife had a honeydo for me to help with, so I put it away for the weekend.

I haven't gotten back out to look at it, but my wife went out and cranked it this morning (easily) just to see if it would. It cranked easily, (so the spark plug was the issue all along) but the motor was shaking and she shut it down quickly.

So, where do I start?
 

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Re: Snapper 7800597 (700 series) Self Propelled

If you move the throttle, see the throttle move, and still no reduction rpm's you may have a broken throttle shaft in the carb.

Make/model of the engine would sure be helpful...

So we are all on the same page, when you say it's hard to crank, to me that means the recoil rope is hard to pull, like you have some clippings built up on the underside of the deck and is causing resistance when the blade turns as the rope is pulled.
What do you mean exactly by "hard to crank" ?
Crank to me simply means the engine turns over.
Hard to start to me means it turns over (cranks), but does not start.

You mentioned hard to crank (start ?) when hot and cranked (started ?) easily when cold. I do know that a coil can exhibit those symptoms when its beginning to fail.
 

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Discussion Starter #3
Re: Snapper 7800597 (700 series) Self Propelled

What do you mean exactly by "hard to crank" ?
Sorry. Probably a poor choice of terms. Traditionally, this engine has started up with 1-3 pulls. It had gotten to the point where it wouldn't start at all, or if it did, it took 5-8 pulls. I attribute that to the quick buildup of carbon on the plug; I didn't check it sooner because it hadn't been in there for long.

The engine is a Briggs and Stratton 128t02-0112-b1, Quantum 700 series manufactured in March 2011.

Steve
 

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Discussion Starter #4 (Edited)
Re: Snapper 7800597 (700 series) Self Propelled - Fast Idle

NOTE: Numbers are B&S part numbers so you can see the parts I am discussing.

I took the mower to an older friend of mine and he looked it over.

The bolts holding the carburetor onto the engine were a touch loose, so he tightened them up. That did not impact the over-reving problem, but he used his finger to manually move the air vane and it had some impact. He recommended I go pick up a replacement air vane spring (790849), so I did.

Once I got the mower onto my workbench and looked at it, I noticed that adjustment of the throttle lever has no impact on the actual throttle shaft (696565). The governor spring (691851) applies suitable forward tension to actuate the throttle in that direction, but the mechanical governor link (691829) does not seem to have any opposing tension. I can't find an exploded diagram that shows what the opposite end of the link is attached to, so I'm at a bit of a loss as to what is supposed to pull the throttle gate closed. Anyway, the result is that the throttle gate is staying open at all times.

I pulled the carburetor and the throttle shaft turns to open the gate and close it freely.

I'm not opposed to buying a new carburetor for $45, or to replacing the throttle shaft for $10, but I'd like to know if I'm going the right direction before I do it.

Any assistance would be appreciated.

Steve
 

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Discussion Starter #5
Re: Snapper 7800597 (700 series) Self Propelled

:bump9:
 

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Discussion Starter #6
Re: Snapper 7800597 (700 series) Self Propelled

Sigh.
 

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Discussion Starter #7
Re: Snapper 7800597 (700 series) Self Propelled

Link to video where I have finally figured out how a governor works, but not why mine is not adjusting the idle appropriately. No one seems to have any input, so at this point, I am documenting it in case someone else searches the site for a similar problem.

https://youtu.be/vUh30QWxtZw
 

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Discussion Starter #8
Re: Snapper 7800597 (700 series) Self Propelled

The gentleman that I got this mower from had an identical motor that he gave me, and I swapped it onto the deck. When we cranked it after the swap, there was some slop in the starter, and when my son tried to crank it the next day, it would not recoil.

I pulled the starter housing off the motor and one of the plastic "wings" from the starter fell out, so I swapped the starter off the other motor and I now have a working motor on the mower.

These mowers were formerly used for commercial mowing, and the "replacement" motor was manufactured the same year as the one I had first, but is a high hours motor that was pulled and replaced 2 years ago. It idles a bit rougher than the one we had. I also noticed after running it for about 5 minutes that there was a light gray smoke coming from the top of the motor (out through the holes in the engine cover).

I'm not sure at this point what would cause smoke at the top of the engine. I'm hoping that this motor will suffice while I get another mower working, and then I plan to take both of these motors to a friend and get him to help me rebuild one good one.

Thanks for looking,
Steve
 

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Steve--I just saw your visitor msg. to me about this post-

OK--I went back and changed the title, and this will bump it back to top of list..
:fing32:
glenn
 

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Sorry I'm a little late to chime in but the over revving on a flat head Briggs when everything else functions properly can be caused by a cracked intake tube, it is plastic, or the O ring that goes between the carb and intake is no longer sealing. I have seen this happen from time to time.
 
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