Runs rough at high rpm

revans

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I have a 17.5 hp briggs and stratton it runs rough and back fires at high rpm runs smooth at lower rpm I have adjusted the valves cleaned the carb replaced the spark plug new airfilter new fuel filter.
 

bertsmobile1

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I have a 17.5 hp briggs and stratton it runs rough and back fires at high rpm runs smooth at lower rpm I have adjusted the valves cleaned the carb replaced the spark plug new airfilter new fuel filter.

We can not see hear or smell you engine,
So we have no idea if you are talking about a horizontal twin , side valve single , overhead V twin or OHV single,
Runs rough is about as good to a mower mechanic as you walking into your doctor & say "I don't feel well".
Just like a computer , garbage in = garbage out.
So if you really want help full Model number then describe
1) exactly how it is running rough
2) exactly what you have done.
There is a massive difference between squirting some carb cleaner down the throat & ultrasonically cleaning a dissasembed carb.
Then a little about yourself helps as well mechanical aptitude, length of time playing with engines etc etc etc.
 

Boobala

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Bert is simply trying to say the folks here need to know certain things about the machine that is your issue ...
see example , and supply the info requested ( as much as possible)

GET INFO.JPG .... click to enlarge
 

revans

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Hi I am Rick
Ok my mower is a Craftsman 30" deck Model # 917.280330 sn# 030309A002530 Engine Briggs and Stratton Model # 31C707 Type # 0603B1 Code # 081205ZE
My self I am a certified aircraft mechanic, I restore old cars for a hobby, I started keeping my lawn mowers running when I was 10 years old and have been doing so ever sence I am 64 now. I also keep my motorcycle and boat running. Ok now about my mower what i mean about run rough at hi rpm is it fires right up runs very smooth from idle to about mid throttle from there to full throttle it runs rough rpm up and down and pops out the exhaust. I have checked the key on the flywheel to crank it is fine I adjusted the valves I did it cold and I set int. valve at .004 and exh. valve at .006 I removed the carb disassembled it I found nothing but I cleaned it out with carb cleaner and blew it out with compressed air. Put it back on fired it up and check for any leakes around carb and intake found nothing. I did a leak down test I did it on a cold engine got about a 20% drop. I put in a new spark plug and a new gas and airfielter. also gas is fresh.I was going to post a picture of my mower but i can not figure out how. thanks in advance for any help.
 

BlazNT

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Clean the carb better. I use an ultrasonic cleaner, air compressor or in other cases run copper wire strands through the holes in the carb. You must clean it very well. Do not run the air from the bottom of the carb it needs to be blown from the carb throat back to the bowl. Same with the wire.
 

bertsmobile1

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Hi I am Rick
Ok my mower is a Craftsman 30" deck Model # 917.280330 sn# 030309A002530 Engine Briggs and Stratton Model # 31C707 Type # 0603B1 Code # 081205ZE
My self I am a certified aircraft mechanic, I restore old cars for a hobby, I started keeping my lawn mowers running when I was 10 years old and have been doing so ever sence I am 64 now. I also keep my motorcycle and boat running. Ok now about my mower what i mean about run rough at hi rpm is it fires right up runs very smooth from idle to about mid throttle from there to full throttle it runs rough rpm up and down and pops out the exhaust. I have checked the key on the flywheel to crank it is fine I adjusted the valves I did it cold and I set int. valve at .004 and exh. valve at .006 I removed the carb disassembled it I found nothing but I cleaned it out with carb cleaner and blew it out with compressed air. Put it back on fired it up and check for any leakes around carb and intake found nothing. I did a leak down test I did it on a cold engine got about a 20% drop. I put in a new spark plug and a new gas and airfielter. also gas is fresh.I was going to post a picture of my mower but i can not figure out how. thanks in advance for any help.

:welcome:

Thanks Ric,
much better we now know what you are talking about and at what level to pitch advice.
Whip the rocker cover off and check the valve lift.
Both the valve are the same length & the cam lift is the same on inlet & exhaust so they should sit the same height closed and when open be similar heights allowing for variations in the valve lash.
ME thinks you may have a worn cam.

Which brand of carb is fitted to your mower ?
Finally to post a photo it needs to be on your computer.
Click on the photo image icon under & slightly left of the attachment paper clip icon, in the middle task bar directly above the typing window.
A widow opens up and hit the From computer button then navigate to where ever the photo is.
One of the easiest forums to put pictures on.
 
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