Motorcycles, Snowmobiles, Go-Carts, ATV's and Golf Carts - briggs and stratton 3.5hp

hey everyone...
me and my friend have been having trouble with this engine...its a briggs 3.5hp horizontal shaft motor....
when we pull the starter it will try to start but it just wont fire up...every now and then it will produce a large spark(5 or 6 inches) out of the exhaust...and some times i can see white smoke come out of the carb intake, and some times the starter will want to pull back on me. i removed the carb and cleaned it out...ive replaced the oil....i made sure the throttle is hooked up and all....
does anyone know what could be wrong and what i could do to fix the engine? thanks

Hello slash bmxer09!

Sounds to me like the flywheel key is sheared.

can you explain how i would fix this because i have no idea about it beyond the carb

Safety first :) Disconnect the spark plug wire.

There is a metal shroud on the side of the engine where the pull starter is. Remove the shroud.

Depending on your engine you will have either a metal cone with a big nut at the bottom or an aluminum housing thing in the center of the flyweel. Remove the large nut or aluminum "thing" by turning it counterclockwise (when you are facing the flywheel). You will have to hold the flywheel to keep it from turning.

One the nut is off the flywheel may come right off or you may have to coax it with a rubber mallet or a block of wood to knock it free from the shaft.

Briggs uses an aluminum key (a small square shaped piece about half an inch long) between the crankshaft and flywheel. They do this so if the engine backfires hard or if something suddenly stops the engine this aluminum key sheers in half and saves the engine from further damage. Your engine is timed by properly aligning the flywheel on the crankshaft. When the key sheers (even partially) it throws the timing off.

Get a new key (less than a dollar) and put everything back together.

is that what explains the large spark? cause i dont see how...

The wrong timing can cause many problems. If the spark is too late the fuel will still be burning when the exhaust valve opens so you can see flame & sparks out the muffler. If the spark is advanced too much the fuel is ignited too long before the cylinder reaches the top of it's stroke causing it to back fire or to "puff" out the carb. With the key sheered the timing can be moving all over the place so you may see something different each time you pull the starter rope.

last time i opened the engine that was 1 piece...is this the part that needs to be replaced? i have more pictures if needed

<img src="http://img74.exs.cx/img74/3724/key9pu.jpg" width="122" alt="Image Hosted by ImageShack.us" />

Aha! You found the problem! Yes, that is the flywheel key. The flywheel nut or starter clutch must be tightened well to prevent this from happening again. Also, do not use oil or grease or any lubricant on the crankshaft where the flywheel mounts or it will shear again. This key is what times the ignition.