brigs and straton engine q

[kf4anm]

any masters of the briggs around. A few weeks ago I scored a cherry 12.5 horse craftsman 42"deck riding lawnmower on craigslist for 50 bucks. I changed the plug, oil, fuel filter, and aircleaner. It fires on the first turn like clock work. When its idling with the choke off it has a surge until you engage the blades, then it smooths out and sounds like a champ. My uncle tells me under the carb, all briggs have an air adjustment that will smooth out the idle surge. Is it worth messing with or is that a normal thing. My first riding mower. I plan on using it with a small trailer to haul firewood around the yard so I want it to be efficient without the blades engaged.

cheers

[HobbyMan]

Make sure the linkages on the carbureator are set up correctly. If they are not in the correct holes, the engine will "hunt" I had similar problems and I found out my linkages were wrong when I reassembled the carb.

[Jerry]

Many years ago I was dong quite a bit of work on small engines. Pop into your local small engine shop and pick up a manual for B & S engines; they are excellent with exploded views, parts diagrams, and tuning information. You can also get a catalog that list all the replacement parts and accessories; one of my main taks was replacing older points systems with the Magnetron electronic kit. Catalogs are also available on-line directly from B&S:
http://www.briggsandstratton.com/maint_repair/
One note: clean the fuel tank. Most B&S designs worked well but collected water at the bottom of the tank.

[egsols]

I not that familiar with the bigger ones, but the smaller ones usually had a vane driven governer that was linked to the carb and held with a spring. There were usually a couple of holes on the linkage for adjustment and if not it was adjustable by bending the linkage.

If it smooths out when its under load, i.e. putting the blades on, then when you try hauling with it, the extra load should smooth it out as well. Sometimes on the smaller ones the vane would break or crap would accumulate causing the governer to stick.

Just make sure all linkages are clean and free moving, all should be okay.

Like Jerry said, a service manual is usually a good idea....it'll give the model specific setup and adjustment specs.

[bigb9582]

try turnig the bottom screw in or out a little to see if that helps. keep note of were the screw was so u can put it back if it doesnt help.
i have a older craftsman 11 hp briggs and it starts doin that when the screw vibrates around a little. see there is a spring on the adjustment screw that keeps the screw in place, my spring is worn out so about once a month i have to re adjust it. i plan on replacing it just never got around to it.
what it sounds like is when u put a load on the engine, the engine starts to suxk in more gas, but a idle its not sucking enough gas. try richen it up a little with the bottm screw.

[XSPastor]

I have that exact mower and rebuilt the engine recently. If the carb is clean then it is most certainly the main jet screw that needs adjustment. (This is the screw on the bottom of the float bowl.) Warm up the engine. First, put the throttle up to full. Turn the main jet screw clockwise untill it stumbles and make note of that setting. Then turn it counter-clockwise untill it stumbles and make note of that point. The correct setting is half way between the two settings. If it still stumbles when engaging the blades, back it out counter clockwise a 1/4 turn at a time untill it stops.