3.5 briggs and stratton rough idle - HobbyTalk
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post #1 of 34 (permalink) Old 04-28-2008, 03:50 PM Thread Starter
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Unhappy 3.5 briggs and stratton rough idle

i have a briggs and stratton engine mounted on a lawnmower.
model 10D902
type 0129 B1
code 03021754
starts ok but runs very roughly surging and dropping, can see the governor moving back and forward with surges.
fuel,oil and spark plug ok.hope someone can help
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post #2 of 34 (permalink) Old 04-28-2008, 05:07 PM
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Remove and clean carb, then install new carb diaphragm B&S P/N 795083.
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post #3 of 34 (permalink) Old 05-01-2008, 01:33 PM Thread Starter
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hi tommyj3 removed and cleaned carb fitted new diaphragm but its still idling roughly any ather sugestions. thanks
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post #4 of 34 (permalink) Old 05-01-2008, 02:05 PM
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What I would do is put about 2 ozs of fuel additive in a full tank of gas. Start engine let it run, and see if the additive cleans any crud that may still be in the carb. I personally use Sea Foam Fuel Additive for this.
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post #5 of 34 (permalink) Old 05-01-2008, 04:09 PM
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When you removed carb and cleaned it, did you check the fuel inlet pipe and clean it as well? I'm not sure if this has the screen on the bottom of the pipe or on the side, but in either case, a dirty inlet can starve the engine and cause it to 'hunt'.
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post #6 of 34 (permalink) Old 05-02-2008, 08:36 AM Thread Starter
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hi,yes cleaned the gauze at the bottom of inlet pipe.took it apart again and cleaned blew air through jet and body ,still idling roughly ,racing and slowing down.
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post #7 of 34 (permalink) Old 05-02-2008, 11:59 AM
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did you put the gasket and diaphram on the correct way? if you didn't put those on than it will not run coreectly
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post #8 of 34 (permalink) Old 05-02-2008, 12:11 PM
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rough running

Quote:
Originally Posted by pyro_maniac69 View Post
did you put the gasket and diaphram on the correct way? if you didn't put those on than it will not run coreectly
remove and check spark plug. It could be fouled partially. After cleaning check gap. REinstall. if still rough then the mixture screw may be at fault. Use a screwdriver to first adjust lower screw 1/2 turn either in or out. If problem still exist go to top screw and turn 1/2 turn inand out. Your problem can be old gas also. If all these dont correct the problem them it could be the points. check back later...
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post #9 of 34 (permalink) Old 05-02-2008, 10:45 PM
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oh, I'm sorry, I didnt look at the model number, I was unaware it was an older style diaphram carb
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post #10 of 34 (permalink) Old 05-02-2008, 11:08 PM
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Quote:
Originally Posted by pyro_maniac69 View Post
oh, I'm sorry, I didnt look at the model number, I was unaware it was an older style diaphram carb
It's not that old, and there are no adjustments on this carburetor skytronic, so don't look for any. It is possible that old gas can cause a problem, your engine has no points either solid state ignition, a partially sheared flywheel key can cause a rough running engine too.

Pyro, this is a pulsa prime carburetor, your inquiry about gasket and diaphragm orientation is a valid question.

Last edited by 30yearTech; 05-03-2008 at 01:03 AM. Reason: update
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post #11 of 34 (permalink) Old 05-03-2008, 01:21 AM
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ah ok, I saw the 10D model number and thought that it might have been an older model series

thanks 30year
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post #12 of 34 (permalink) Old 05-03-2008, 01:22 AM
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I REALLY need partsmart on my computer or something
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post #13 of 34 (permalink) Old 05-03-2008, 01:39 AM
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I REALLY need partsmart on my computer or something
You can find parts look up and various sites on line, like partstree.com, jackssmallengine.com and of course briggsandstratton.com, may be a little slow if you have dial-up but otherwise pretty useful for looking up or at IPL's
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post #14 of 34 (permalink) Old 05-19-2008, 09:01 PM
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Very similar question

I think I have the same basic motor and carb. Mine is Model 9D902. This is a small Murray mower with the "throttle free" carb. Someone left behind when I moved in and looks to be used very little.

Prime it and it cranks first try and runs like a scalded dog for 5 minutes then slowly cuts off like when they run out of gas. Prime again and runs great for another few minutes and repeat.

Odd thing is it ran for 20 or 30 solid minutes the other day while I was weeding a rough, steep drainage ditch area. Tilting up/down/sideways pretty much the whole time. Then moved back to the level yard and off it goes after a few minutes.

This has got to be a fairly simple problem. Anyone know what is going on?
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post #15 of 34 (permalink) Old 05-19-2008, 09:38 PM
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Fuel pump diaphragm may not be pumping fuel into the pickup area, operating on an incline and fuel can make it's way to the pickup without the diaphragm pumping it there. Probably a new diaphragm in the carburetor will take care of the problem.
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