OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S 12.5hp v twin cylinder help, please.

B&S 12.5hp v twin cylinder help, please.

I have and old yardman ride on.

When I turn the key to start it, it will spin a little then it hits compression, and stops. Apparently this is because the de compression device is not engaging.

The reason it is not engaging is because the tappets need adjusting, as they are too loose and have too much gap.

This means that also the engine will not be getting a full breath of air as well.

Also, not sure if this will due to the slack in the tappets, but the engine will only run on full choke. When choke off, engine revs up and down like a v8 with a lumpy cam, and stops.

I think this is because the tappets and valves are not opening enough to let in enough air/fuel. But when on full choke there is a stronger fuel mix and therefore the engine runs.

I also notice, heaps of fuel leaking out the front of the carby/ air filter area.

This all might have to do with the choke on full, and tappets/valves.

What do you all think?

Also is there a service manual or instructions I can get my hands on for this job?

Cheers,

Peter

hi peter,
to find out the valve clearances we need to model type and code numbers found on the cowling of the engine. also is the engine a over head valve unit or a l-head block. from the description it sounds like it is a OHV but we need to be sure.
as to the carby and running problems there are many possible causes, but if re-adjusting the tappets does not fix it i would consider putting a carby kit through, especially if it is leaking fuel.
i agree with you though that the resistance during starting is caused by sloppy valve clearances as briggs and stratton design the cams so the exhaust valve is slightly open during to compression stroke so it is easier to spin over. they say there is no effect during running though, which i am a makes me qringue a bit.
anyway good luck!
regards jay

If that is the OHV V-twin, I'm told it has a decompression device as well as the EzySpin feature mowernut referred to. That engine will not crank unless the decompressor is working, and it will not work unless the tappet clearance is just exactly right - it seems to be extremely sensitive. So, you need to attend very carefully to the tappet clearance as your first move, to get it to crank and start.
The valve clearance, and the valves, have nothing to do with your other problems. You have a fuel feed or carburetor problem. We will need more information to diagnose that one, but meanwhile fix your decompressor before you damage your starter motor.

welderman,

I would remove the cylinder head and check for carbon around the valves because it could be stopping the valves from closing properly causing all sorts of issues.

We do require more information as grumpy said like the model type and code of the engine and that way we can give you correct clearances for the valves etc.