Briggs & Stratton 6HP engine acting weird


Old 01-27-04, 03:39 PM
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Unhappy Briggs & Stratton 6HP engine acting weird

Mower Info:
Briggs & Stratton 6HP Quantum XTE. Self propeled. for picture of mower

I bought this mower used from a local home depot about 5 years ago. It worked flawleslly for a good 2 years, oil changes, maintanace performed regularly. After 3 years I stored it and didn't used it for 3 years. I took it out today to test it. Here what happened:

- The oil I check it still good
- After priming it, and 3 cranks the engine started. The idle speed and noise seem normal.
- When i pull the throttle to mid range it sound, as it should.
- But when I pull the throttle all the way the engine would accelerate and then decelerate, accelerate and decelerate again.

+ I check the air filer. It clogged with dried grass -- I cleaned it
+ I check the oil. It all good.
+ I check the sparkplug, it look clean. replaced with new sparkplug, still same problem

I obsevered that when I pull the throttle all the way up, the air intake metal plate that located inside the intake tube would open and close ( open accelerate, close decelerate). I held the metal part that connected to a spring that connect to the throttle controler cable to keep the metal plate constantly open so air flow in freely, when i do that the engine run at maxed speed no increase or decrease of acceleration. I believe the part in purple circle is the cause of this problem... it seem to pull the metal plate to close the intake when rpm too high.

Any help will be appreciated. thx
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Old 01-27-04, 04:37 PM
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The spring you have pictured is part of the governor system. When you adjust the throttle you are really only adjusting the tension on that spring and the governor inside the engine is what really advances the throttle. It sounds like all that really needs to be done is to adjust the high speed mixture screw on the carburator. I had that exact same problem with my snow blower this morning when I went to remove the snow we got last night. The motor speed would oscillate up and down. A simple adjustment of the mixture screw about one half a turn was all that was necessary. Just keep track of where the screw is before you turn it so you can turn it back to the origional position if the adjustment doesn't have an effect.
Old 01-27-04, 04:40 PM
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Location: NW Georgia
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Before you adjust the high speed screw give the carb a good cleaning and make sure the holes in the high speed needle are clear and open.

Make sure you clean the carb well then start her up and see what's what ... BEFORE ... you make any adjustments.
Old 01-27-04, 08:33 PM
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Location: southern louisiana
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Probably what happened was that trash collected over time in the tank and when you started it, the trash got sucked up into the carburetor thus slowing down the flow of fuel to the point that it wouldn't allow enough fuel to keep the engine running wide open. You could make a small adjustment on the needle screw but that would be a quick way of bypassing the real problem. A good carb cleaning would be the real fix.
Old 01-28-04, 05:53 AM
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Thanks for the insight guys, I'll look into this afternoon. I found a cleaning solution for Caburator and metal parts.. for $60 a stiff price. Is there any cheaper way, and how do I clean it. I will try to adjust the screw If i can find it.

Thanks again
Old 01-28-04, 11:09 AM
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You should be able to find a one-gallon can of carb cleaner called "chemdip" at most auto parts stores. I believe autozone and advance carries it. Automotive carb cleaner in an aerosol can might do well enough to get the job done too. Just be sure to wear safety glasses!
Old 01-28-04, 06:30 PM
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I agree that a carb cleaning is in effect. Just do a very good job on the cleaning without screwing up the carb insides.
Old 01-31-04, 11:31 PM
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Cleaing job done right ?

I bought a spray can that labled caburator cleaner. With engine off I sprayed into the intake hole untill it litterly flooded. After that I wait 5 minutes and then full the string lightly and slowly to let the excess cleaner escape by the exhaust.

Result: The engine run at 3/4 rpm without isolating. Almost no improvement. When i hold the string ( open the metal plate to all the way ) and pull it to make it run at max rpm, the rpm start isolating.

Are these engine designed to run at 3/4 of their potential rpm like cars? or this is a bad job of carb cleaning. I repeated the cleaning job couple time but still no good result.

Where is the "adjustment" screw on this particular model? there seem to be none, I know they must have one some where.. just couldn't find it. Note: I have't took the caburator off the engine block yet.

I saw some aditive for cleaning fuel system for car, you think this will help with my mower if i use it as fuel cleaning solution?

A final question: What rpm range should a mower be running at, 3/4 4/5 or full throttle... ?

Thanks for your help guys, as always really appreciated
Old 02-01-04, 02:32 AM
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You need to go back to cleaning the carb again. Spraying the carb externally won't do any good at all. You will need to remove it and disassemble it. At least pull the bowl off the bottom of it and clean it out and make sure there is no water in it. The engine should be used at full throttle.
Old 02-01-04, 11:56 AM
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I took the carb apart, sprayed with the cleaner, then wash it with water, then dried it then used my mouth to blow into the holes, after that I repray the whole caburator with cleaner. Reinstalled it and problem still there.

I notive when running without the air filter it a bit better, so I'll go head and change air filter and ask the technician there what else could be wrong with the mower

a note: I took apart the carb and couldn't find any screw for mixture adjustment. Does this model even have one... ? I bought it used dont have manual

Thanks cheese man and all others
Old 02-01-04, 10:15 PM
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Depending on the carb used, there may not be/probably isn't any adjustment on that carb. If it is surging, it is still not getting enough fuel. The bowl screw that you remove to drop the bowl has holes in it that need to be clear. There is one going down through the center, and one going through the side. Make sure they are completely cleared out. That's where the problem usually is.

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