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briggsman65
05-05-2007, 09:26 PM
It is a 3.5 horsepower briggs motor. ( model #9D902) When I start the mower up it runs weird. It runs at an up and down speed. Runs full idle then almost dies repeatedly. I took the carburator off and cleaned it. I cleaned the fly wheel and the armature. I changed the oil. I changed the spark plug. I also changed the air filter. The only thing I am noticing that is odd, is the spark plug keeps turning black. I can clean it and put it back in and it turns black again. I can't think of anything else to do. HELP!!!!!!

Thank-you ahead of time for your help.

Restrorob
05-05-2007, 10:25 PM
In what way did you clean the carb. ?

Did you make sure the main jet was fully open (not restricted) ?

Did you install a new diaphragm ?

Sounds like it's running lean causing the hunt (up/down running). When a engine does this every time it goes up it's pulling more fuel than required to maintain a steady speed, That could account for the black plug.

briggsman65
05-05-2007, 10:30 PM
I just took it off of the gas tank and sprayed it with the carb cleaner. it is one of those "fancy" plastic carburators. I cleaned the screen and the pick up tube and all of the dirt. I did not replace the diaphragm. Do you think that it needs to be replaced? I didn't really pay attention to the main jet as far as adjusting. Didn't see how you would open it up.

Restrorob
05-05-2007, 10:51 PM
The main jet is shown below. There is no adjustment, Spray cleaner through it and make sure it's open. I would suggest replacing the diaphragm. These plastic carbs are not the best at sealing.


http://i107.photobucket.com/albums/m314/Restrorob/Briggs9D902Carb-1.jpg

briggsman65
05-05-2007, 11:33 PM
Cool.................Thanks I will try this and also thanks for the diagram with the part numbers.:)

Bill Kapaun
05-05-2007, 11:56 PM
Just curious-
Does that carb have a choke?

Restrorob
05-06-2007, 08:23 AM
Just curious-
Does that carb have a choke?

No Bill, It has a primer bulb and reference # 913 is the primer check valve assembly. I don't remember ever having a problem with this assembly to cause a rich run/hunt situation but anything is possible.

briggsman65
05-06-2007, 03:43 PM
No choke...........just as Rob is saying. I will order diaphragm tomorrow and let you know if it works when I get it.

Bill Kapaun
05-06-2007, 04:10 PM
Briggs PN is 495770

http://www.odref.com/briggsandstratton/model-09/9D900-ms4864-1002.pdf

Turfinator1
05-06-2007, 06:20 PM
I Brought a power washer with a briggs on it and i took it back the next day because it would take 15 pulls to get it started and it would run for hour and then I would shut it off and then I would have to pull and pull and choke it after it had been running to get it back started.