25 hp lawn tractor has RPM surge when run at med hi RPM: John Deere Review  -- John Deere Tractors Discussion Forum and Review 25 hp lawn tractor has RPM surge when run at med hi RPM: John Deere Review -- John Deere Tractors Discussion Forum

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 08-25-2004, 06:18 Post: 94398
Scott1*
2004-08-25 06:18:01
Post: 94398
 25 hp lawn tractor has RPM surge when run at med hi RPM


I have a 25 hp 48 inch lawn mower that revs. up and down when the throttle is half way up or higher. It still cranks and runs but it's performance is impacted besides the fact it just sounds terrible. Ruuummmmm.........Ruummmmmmm....... Rummmmmmmmm.......

Any help is appreciated. I checked cleaned spark plugs and replace part of the fuel line that looked like pretty bad but it's still doing it.

Thanks,
Scott






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 08-25-2004, 07:28 Post: 94408
beagle

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 25 hp lawn tractor has RPM surge when run at med hi RPM

Three things to check first:

You replaced part of the fuel line, but did you replace the fuel filter. You have classic clogged filter syndrome.

Could be a glogged jet in the carburator. Have the carb. cleaned and adjusted. There are ususally two jets, low rpm and high rpm.

Govenor is out of adjustment. Sometimes with a lot of hours on a gas engine, the govenor spring gets tired. Does this problem happed under load or no-load situations. Under load would usually point more to a carburator or govenor problem.

Check the filter first if you haven't already. That's the most likely cause.






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 08-25-2004, 08:16 Post: 94411
shortmagnum

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 25 hp lawn tractor has RPM surge when run at med hi RPM

If it's an air cooled engine I'm thinking that it's a dirty governor. If they get sticky they don't react as fast to rpm changes as they should. Or beagle's weak spring idea could do the same thing.
Dave






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 08-25-2004, 08:36 Post: 94414
Scott1*
2004-08-25 00:00:00
Post: 94414
 25 hp lawn tractor has RPM surge when run at med hi RPM

Nice pics short mag.. Thanks for the reply. It's a briggs and stratton engine and air cooled. Although I have the owners manual on the mower (Scott's built by Deere) it does not go into a lot of detail on the engine. Any idea where I can get this info on-line so I can see what you guys are talking about.

Thanks.






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 08-25-2004, 08:56 Post: 94417
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 25 hp lawn tractor has RPM surge when run at med hi RPM

Thanks for the reply.

oddly enough when cutting high grass (under load) the symptom litterally goes away...

I'll go ahead and replace the fuel filter you can see junk in there.

Thanks






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 08-26-2004, 07:13 Post: 94579
Art White



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 25 hp lawn tractor has RPM surge when run at med hi RPM

Your problem could be about three different things. What model engine do you have?






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 08-26-2004, 09:51 Post: 94594
jsolse



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 25 hp lawn tractor has RPM surge when run at med hi RPM


It's a 25 HP Briggs & Stratton i/c OHV. I'll take any advise. Thanks!






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 08-31-2004, 17:05 Post: 95123
Normando

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 25 hp lawn tractor has RPM surge when run at med hi RPM

Here is my two cents.

I have seen this sort of thing on small motors so I think it may pertain. When the air fuel ration is off, the motor will leans out. The governor tries to compensate by either open or closing the throttle, which in turn causes the motor to surge. Either the fuel filter is plugged or the carburetor mixture screws need to be adjusted.






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 09-06-2004, 10:37 Post: 95698
lbrown59

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 25 hp lawn tractor has RPM surge when run at med hi RPM


It's a 25 HP Briggs & Stratton i/c OHV.
=============================
jsolse
=================================
***************************************************
I have had this problem almost from day one with an I8 HP Briggs & Stratton i/c OHV. on a 1995 wards lawn and garden tractor that I bought new.
During the 3 year warranty I bet I had it in for this problem 12 to fifteen times.
They never did get it corrected.
After that I took it to another service shop 4 to six times that 4 th. year for the same problem and they weren't able to get the issue resolved either.
I finally replaced the carb with a new one about 3 or 4 years ago.
Thought I had it made then as it ran like a top and the best it had ever ran even when the tractor and motor was new.
Guess what that only lasted 2 or 3 months with the new carb then it was right back to the old routine.
The Carbs on these engines aren't worth a crap.
I have been running it with the choke pulled out about an inch for four years now.
I let it run till it warms up then pull the choke out till it starts flooding out then slowly push it back in till it starts surging then pull it back out slowly until the engine smoothes out.
This is the only way I can get it to run well enough to use the tractor.

I think Briggs has a serious design flaw with the carburetors on these engines.

















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 09-06-2004, 12:23 Post: 95704
Chief



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 25 hp lawn tractor has RPM surge when run at med hi RPM

Try running a slightly tighter spring on the engine govenor. I had a 3.5 hp B&S that did this as well as not reving up to a reasonable rpm. I clipped a couple of coils from the spring and reinstalled it. This did the trick BUT be very careful doing this as you can cause the engine to over rev. under no load conditions. It is a matter of trial and error until you get it the way you want it. Of coures, this will void your warranty if it still is under warranty. In that case take it back to get it fixed.






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Discussion Boards > Active Subjects > Messages as Posted > John Deere Review Forum

Thread 94398 Filter by Poster:
Art White 1 | beagle 1 | Chief 1 | jsolse 2 | lbrown59 1 | Normando 1 | rklindt 1 | Scott1* 2 | shortmagnum 1 |




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