3 hp flat head

[Miniwood]

3 hp briggs flathead Knocking heavy under load and missing. Cleaned carb and have good fuel in tank. New plug !
Pullet head,,, top of piston and valves covered in carbon ( bad) .
Cylinder looks great . Valves seem to seat ok ( not super tight) haven't checked gap yet!
Suggestions?

 

[we4amigos]

Timing ? You may have slightly sheared your flywheel key,,,or severely sheared it. lol But timing can,,but not always,,be your knocking/detonation problem. Which in-turn lead to carbon build up.
Take a close look at that key
Good Luck

 

[Miniwood]

Key is good / snug fit

Timing ? You may have slightly sheared your flywheel key,,,or severely sheared it. lol But timing can,,but not always,,be your knocking/detonation problem. Which in-turn lead to carbon build up.
Take a close look at that key
Good Luck

 

[Miniwood]

Found it
No gap at all on either valve.

Timing ? You may have slightly sheared your flywheel key,,,or severely sheared it. lol But timing can,,but not always,,be your knocking/detonation problem. Which in-turn lead to carbon build up.
Take a close look at that key
Good Luck

 

[Miniwood]

Gap on
91202 ??

 

[Miniwood]

Key was fine , valves had no gap and piston rod was really worn on the crank.pressure ring was at.020 but got new rings anyways because it was really weak. Ordered rings rod and CC cover gasket under $20 shipped on ebay

Timing ? You may have slightly sheared your flywheel key,,,or severely sheared it. lol But timing can,,but not always,,be your knocking/detonation problem. Which in-turn lead to carbon build up.
Take a close look at that key
Good Luck

 

[Richard Trotter]

Your valve lash should be .005-.007 intake .007-.009 exhaust

 

[oldfatguy]

normal maintenance on the briggs calls for taking the head of to clean off the carbon build up. You could have an issue with the rings causing it to burn oil. Do you notice any smoke ?

 

[Miniwood]

Not smoking but lots of carbon inside,,,, also no valve gap. Noticed the piston ring gap was not too big but the rings seemed weak and piston could be moved (side to side) around inside the cylinder fairly easily if that makes sense.
Just got the new rings today and they are thicker and much stiffer than the old rings. Piston is now nice and snugg in the cylinder with the correct gap!

I really Think the old rings were getting weak and brittle if that can happen?

normal maintenance on the briggs calls for taking the head of to clean off the carbon build up. You could have an issue with the rings causing it to burn oil. Do you notice any smoke ?