# B&S 12.5HP very high RPM



## Puter (Jul 31, 2009)

This has probably been fixed many times, but I am a newbie to this forum. It was the only one that I found that appeared to have good traffic. I appreciate your time in reading my issue.

A friend has a Murray (Wal-Mart) with a 12.5HP B&S. Standard stuff. He bought a new gas tank because his old was leaking. He told me that it runs very fast. 

I looked, and it indeed is running at a very, very high RPM. The vane governor is working well. I can move the throttle by hand and it screams! I also cannot turn the throttle down to the idle stop or it dies. It seems that the lowest it will run is ~3600RPM and that is with the throttle barely open.

I sprayed the carb with cleaner and made sure nothing was stuck. No help. I soaked the carb overnight in carb cleaner and blew out everything with compressed air. No help. I did make sure that when the float moved upwards, I could not blow into it hopefully checking the needle/seat.

Can anyone give me more clues? 

Thank you in advance!
Ralph


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## bgbass (Jan 11, 2008)

check where the throttle rod hooks to the carb. there usually more than 1 hole put in a different hole and see if that helps


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## Puter (Jul 31, 2009)

Thanks for the reply. No, that did not help. I can manually move the throttle and when it is close to the idle stop it is still running ~3600RPm. that is as low as I can get it. If I try to move it any lower, it dies. Of course, if I move it any more open, it starts to scream where it is running ~5500RPM.

It is also dumping a lot of gas in a way and spitting it back out of the carb a bit. My leg was slightly sprayed when I started it for a friend that came over yesterday. It seems like it is drawing too much gas.

I am thinking my next step is to buy a new float, needle and seat. Perhaps a jet nozzle since it appears that gas is just being dumped into it.


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## bc11 (Jul 14, 2009)

Sounds like a governor problem to me. There was a similar thread on that within the last 3 weeks. I don't remember the guy posting back with what fixed his or if he got it fixed. I had that problem with a 12.5 hp b&S murray 38" rider a few years ago and don't remember how I fixed it or if I took it to the shop. Mine just howled wide open. Mowed with it that way but didn't let it sit cause it sounded like it would blow up. Mower still runs today.

Behind the seat around the fender is the murray number and date code. On the engine on the housing is a model code, type code, and date code. Post back with those numbers. You can go to briggsandstratton.com and find the parts drawing, etc. It could be a missing, broken, or stretched spring. Or it may be the internal mechanism.


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## Puter (Jul 31, 2009)

I also thought it a governor problem. All of the springs are there. The governor seems to be working very well. It will move the throttle plate of the carb as it should when the mechanical throttle is moved. I did copy all of those numbers to the booklet that was given to me by the owner. I'll post them again.

I saw the B&S website. But I clicked to go to the BETA site and I think that I should maybe have not done that. 

Thanks for the reply.


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## Puter (Jul 31, 2009)

Model: 28V707
Type: 1113E1
Code: 970821ZA


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## bc11 (Jul 14, 2009)

I didn't like their beta site either. Didn't give the same drawings. Your engine was built on Aug 21, 1997. If you look at the Murray date code (4 numbers), the last one will probably be a 7 (made in 97) except that they may have changed the numbering system in 1996 so the first number may be a 7. Mine was a 1993 model engine model 289707 1021-01. Since I still don't remember what fixed mine, I must have taken it to the shop. I'm not sure how the inside the governor works. I know a tractor governor has a couple spinning pieces, forget what you call them, that are thrown out by centrifical force where they engage and slow down the governor. Somebody else can explain it better. My mower just kept going to wide open without coming back. The only way to get at it is to open the case. I have a feeling that maybe the spring got knocked off somehow.


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## bc11 (Jul 14, 2009)

Well now my old murray is doing the same thing again. Backfring through exhaust shooting flame 3 feet, missing, and not running on full power and would die in heavy grass when I parked it last Sunday. Yesterday, I fired it up and same thing for a few minutes, then the throttle opened up and acted like it was running wide open with no governor controlling it until it would die when I got into heavy grass. I can work on a carb but not sure about the governor. Seems like I replaced the magnetron once on that one. I did find one muffler bolt loose yesterday and tightened them up before I ran it. Don't think the flywheel key would be sheered and still run. I'm stumped. I can remove the muffler and spray down the exhaust valve. Could go thru the carb is someone thought that would affect the governor. Anyone have any ideas? Thanks.


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## bc11 (Jul 14, 2009)

I ran mine Sunday for a while till it quit. Noticed when I started that one muffler bolt was sticking out. Screwed it in and tightened both of them.

Checked it tonight and it fired twice and wouldn't start. That muffler bolt was sticking out again. Went to remove the carb and the whole assembly was loose. Turns out the top bolt for the carb intake where it screws into the block was gone and the bottom one was loose. Guess I'll get a new bolt and a couple gaskets for the muffler and intake.

Do you guys think it was the loose muffler or the loose intake that made the engine want to run wide open? The more I think about it, this may have been the problem the last time the governor was letting it run wide open.

As much as I usually like to use anti-seize on bolts anymore, I wonder if I should use some loctite? Thanks.


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## Rudy (Jun 14, 2006)

bc11 said:


> Turns out the top bolt for the carb intake where it screws into the block was gone and the bottom one was loose. Guess I'll get a new bolt and a couple gaskets for the muffler and intake.


My dad monkey-rigged the engine from an ancient Rio riding lawn mower to a go-kart I had. I remember one time that the engine was running a little TOO well (yeah, I was going faster  ), and noticed the intake bolts were loose and the intake and carb were dangling from the engine a bit. Tightened them up, and it was back to normal.



bc11 said:


> As much as I usually like to use anti-seize on bolts anymore, I wonder if I should use some loctite? Thanks.


I used to sell Loctite products when I worked for Bearing Headquarters (up until the economy took a dive back in March), and they have many different types of thread locking products. There is a removable Loctite--be sure to use that one, if you use one at all. (Don't recall the color, but it might be the blue.) The more permanent types take too much torque to loosen the bolts. You just want something to snug up the bolts so they don't work loose again.


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## bc11 (Jul 14, 2009)

I picked up the parts yesterday at the local mower repair. They confirmed that a leaky intake anywhere where air bypasses the butterfly which is connected to the governor to regulate rpm will cause the fast rpms. I'm going to try the locking tabs on the muffler bolts but they indicated when the bolt holes start to get wallowed out with bolts backing out, you just about have to go to a little loctite. I got the blue loctite at home. Suppose I'd just start with a thread or two and not get carried away with it.


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## Rudy (Jun 14, 2006)

A little Loctite goes a long way. Put some on a couple of threads, and it should hold OK. It'll distribute itself along the threads anyway, as you screw it in.


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## Puter (Jul 31, 2009)

Yes, the loose intake causes an air leak. I cannot find any such on mine. The exhaust bolts were loose and I tightened that up previously.

I went through the carb a third time. I let it soak for 3 days in carb dip, bought new needle/seat, float, and nozzle. No change/help. I disconnected the governor altogether. Still the same. 

I have not found or done anything to make the symptoms change. I wonder if I am on the right track at all. I am going to try to adjust the governor where the thing will not run, then go from there and see if I can get it to only run ~3600 at full thrlttle lever. The throttle plate is barely open at that point.


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## bc11 (Jul 14, 2009)

Now I remember what fixed mine years ago. The throttle/venturi plate that is closest to the engine and right next to the intake manifold was laying loose and not turning. The screws that screwed it to the shaft were no where to be found and I assumed sucked into the engine sometime.

Do the feel the governor parts move inside the engine. There is some type of vane or something. Don't know much about it or if it might be broke but I suspect if you manually move the governor arm you will feel some resistance inside.


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