Hi,
I have a 6.HP Intek o/c Briggs & Stratton on a mulcher. It hasn't been started for some time. I gave it a birthday, clean fuel, clean carby & air intake filter, dropped oil flushed sump, Checked spark and cleaned plug. (what is the correct gap)? Ran nicely at first just blew a bit of smoke. It ran OK for 15 - 20 min then started to break down under load, as soon as you put the smallest amount of load on the unit the RPM would start to drop and it wouldn't gain blowing smoke the odd back fire then eventually dying.

Checked plug pretty dirty cleaned it, got the unit running again, not better still breaking down.

New Plug perhaps? Can anyone help.

Kindest Regards,

Davnix.

Hi,
Yes, you need a new plug. Gap is specified as 0.025 - 0.032" and I go with 0.028 - 0.030." I would also say that you have a fuel problem. I realize that you said you changed the fuel. Just think for a moment about the old stale fuel that sat in the tank and coated the walls. The new fresh fuel runs well in the engine, but its presence begins to dissolve the varnishes left in the tank by the old fuel. I would think about an additive put in your fuel container and introduced into your mower at the time of fueling. This will help clean the residue and get the fuel volatile enough to combust.
Peace,
Clarke