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doogie_ac61358

Starter help

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doogie_ac61358
Ok guys, heres a good one for anyone who wants to jump in. On a briggs and stratton 11 hp vertical shaft engine, is the starter a positive ground or a negative ground. The problem is that it is spinning backwards and pulling a vacuum through the exhaust. I have it on a negative ground system. Won't put in here what brand of tractor so as not to offend the more sensative members here, just know that I am working on it for a friend. If it is a negative ground starter what could make it spin backwards?

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sandyhillbill
can you determine if the battery is hooked up so the system is negative or positive ground- if it is hooked up with the neg. battery post to frame of tractor then it should be neg.ground.

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doogie_ac61358
Hey guys, I haven't had it apart yet but that may be the case. I have determined that the tractor itself is negative ground. But I haven't determined if the tractor the engine came off of is or not yet. The bendix is working correctly though and if you look at the top of the engine it spins clockwise. I haven't dealt with these kind of engines much. Any other ideas?

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PatRarick
The starter drive will not kick in if the starter is running backwards. The gear kicks in by centrifigal force on a spiral. Running backwards forces the gear down on the spiral, rather than up into the flywheel. Since the starter drive is kicking in and the engine is spinning clockwise when facing the flywheel, there's no problem there. If you're pulling a vacuum through the exhaust with the correct engine rotation, there are several possibilities. The exhaust valve clearance is set too close. A piece of carbon or other foreign matter is stuck to the exhaust valve or seat, preventing it from sealing. The exhaust valve keeper has come off, preventing the valve from closing. The exhaust valve is stuck open either by carbon buildup on the stem, or the valve stem is bent. The valve is burned or the valve head is warped. The exhaust valve seat has popped out.

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doogie_ac61358
Had the head off tonight, looks like there was carbon on the seat. I had no compression before but have compression now. Will be taking the inspection plate off tomorrow and checking the clearance. Does anyone know the clearance and tolerances between the stem and the lifter? Thanks to everyone who threw their two cents in here. I am hoping the get the valve out tomorrow if it won't start now. Will see if it's bent or gummed up or not.

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