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I recently bought this mower at a yard sale and it starts fine but it idles erratically. I bought two little springs to go on the carb from a B&S website and I know where the big one goes but I am not sure how to, or even IF to, hook up the little one. Does anyone have a picture or diagram of this model that might show me where this thing goes? This spring may not even be my problem, but in any case I would like to get it hooked up correctly and then go from there. Also, how does this "throttle-free design" work anyway?
 

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This engine uses the windvane governor (that little flap) make sure thats not sticking. the link from the windvane to the carb has that loop, the springs (both of them) go from that to the lever up front. The throttle free design is just like the one I have........ just has no throttle control up top, you have to reach down to use it on the engine. Things to do, is clean the gas tank and carb if this doesn't help. Cleaning the carb means take it off and blow it out good through all the holes you see good with carb cleaner. Replace the diapragm and gasket (be sure not to fold either, and to remember which is on top)
 

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Discussion Starter #3
Bugman,

Thanks for the reply. I went ahead and put that other spring on there where you suggested, though I am wondering to myself why on earth there would be two springs going from and to the same place, why not just make one slightly stronger spring to go there? At any rate, my problem still persists. When the engine is running it revs up to extremely high rpms (it didn't do that before I put the second spring on there) and then its like it cuts out momentarily and then kicks back in and repeats this cycle over and over. I have cleaned out the gas tank because there was a little water in there, but that was several tanks ago and I really don't think this is fuel related due to the consistency of the cycle of revving up then cutting out. Is there something in the ignition parts that could be causing this?
 

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Ahh crud..... sorry for being a little off with my info. There should be a tab, right close to the "V" that the link from the windvane goes to. That little hole there, the small spring should go to that, the large spring to the lever up front.

As for why they don't use only one.... they used to!! but changed it for some reason. I guess because just the one big spring would stretch out after a while, so they backed it up with another. I dunno

Its not the ignition. If the springs don't help it. (the governor system, as you see is very simple) then a carb rebuild is the thing to try next. The diapragm in the carb can stiffen or get tiny holes in it and make em run rough.
 

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can't say that I do...., I can explain it the best I can...., its two springs (one big, one small) but go from the loop in the link (loop closer to the wind vane flap) to the throttle control up front.. (throttle free design is a cheap way to say it didn't come with a throttle control cable up to the operator at the handle) That link goes from the vane to the "v" looking part on the carb.. Basically moving the throttle left to right, loosens tension or puts tension on the springs...., the wind created by the flywheel pushes against the wind vane.... this in turn opens and closes the butterfly in the carb. Simple design..... you can actually tell on a windy day, that the wind affects this even, but just a little bit. I'd recommend graphite powder on the throttle control, little on each side and work it in.
 

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Briggs & Stratton Classic 3.5hp Model 9D502

Hello!,

I am trying to tune-up a Briggs & Stratton Classic 3.5hp Model 9D502...
I:
removed the head, cleaned it (top of valves, piston head etc.,)
cleaned the carburator,
Gas tank,
air filter,
Changed the oil,
Replaced Spark-plug,
(checked the spark and it is Strong)

Put it all back together, and the mower Runs exactly the same as it did before,
Chokey, Surging from low to high Rpms every once in a while, it's like when you get a piece of dirt in the carb, then it gets free and runs for about 2 seconds then chokes back down, SAME effect with the airfilter on OR off....

Also, when I had the head off, and I rotated the flywheel to move the piston through its cycles when the piston goes down it leaves oil streaks inside the cylinder wall, something doesn't seem right about that, I think the oil is supposed to stay BELOW the Rings.. RIGHT?

Could that cause this issue?

ANY IDEAS???

Help! this mower is a little old lady's mower and I'm just trying to be a help and save her a dollar.
 

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Did you replace the diaphragm in the carburetor???

Sounds like it's leaking and allowing fuel to bypass the jet and enter through the pulse port for the pump.
 

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My normal post;
You need to install a new diaphram kit, it is Briggs part # 795083 or old # 495770 also Lowe's has a kit #5083 which has the same parts.

Here we go;
Remove air cleaner, there are 2 bolts that hold things together, one on the front of the tank 3/8" and one into the block 1/2", remove these bolts, now "slowly" slide the carb/tank off the intake tube and breather tube, now tilt the tank in to release the throttle linkage and waalaa the carb/tank is removed. Remove the 5 screws from the carb/tank remove carb(don't loose the spring) now spray all holes, cracks and crevases in both the carb and tank surface with brake parts cleaner, remove the main screen(looks like a thimble) with a small screwdriver pry out the main jet(carefully) and clean it, reinstall the jet, it can be difficult some times to get it to snap back in place(I use the rounded end of a screwdriver handle). Remove and clean the fuel pickup stem. Clean any junk/rust from the tank. Install the diaphram on the tank then the gasket(no goo or sealer) now carefully replace the carb(the spring will try to misalign the diaphram), tighten all screws a little at a time so as not to crimp the diaphram until they are all tight. Install the carb/tank in reverse order and you are done. If I missed something one of the real mechanics will correct me. Have a good one. Geo
 

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I hope not to sound like a broken record but I have recently taken my Briggs and Stratton Classic 3.5 hp model # 9D902-2005-B2 apart cleaning the internal components. Reason is from it being outside uncovered allowing water to go through the exhaust into the engine. Well, I put everything back together the way I took it apart replacing the carb. diaphram, new spark plug, clean the gas tank, etc. Now it will not start not even firing. Check spark from spark plug and it is getting spark. Can you give me some things to check that maybe keeping it from firing and not starting? Thanks!
 

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you might want to check and make sure your float is functioning correctly. i had the same issue with an old mower i had, and that was the culprit. not saying thats what it is, but its a possibility:)
 

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I hope not to sound like a broken record but I have recently taken my Briggs and Stratton Classic 3.5 hp model # 9D902-2005-B2 apart cleaning the internal components. Reason is from it being outside uncovered allowing water to go through the exhaust into the engine. Well, I put everything back together the way I took it apart replacing the carb. diaphram, new spark plug, clean the gas tank, etc. Now it will not start not even firing. Check spark from spark plug and it is getting spark. Can you give me some things to check that maybe keeping it from firing and not starting? Thanks!
Could possibly have a stuck valve, if it had water in it, then there may be some corrosion sticking a valve.
 

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I recently bought this mower at a yard sale and it starts fine but it idles erratically. I bought two little springs to go on the carb from a B&S website and I know where the big one goes but I am not sure how to, or even IF to, hook up the little one. Does anyone have a picture or diagram of this model that might show me where this thing goes? This spring may not even be my problem, but in any case I would like to get it hooked up correctly and then go from there. Also, how does this "throttle-free design" work anyway?
307430
 
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