burnt exhaust valve

A

ACF

Well-Known Member
have a b/s 31p677-0804-e1 runs for a little bit shuts down, removed valve cover and found that the exhaust valve area was brown and had some build up of some material. i know not best pixs, what would cause this and what repairs do i need to do

thanks
ac
 

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That is residual oil getting cooked due to an overheating condition. The cooling fins under the fan shroud need to be cleaned really well.

There is also a very high chance that the head gasket is failing. This engine design is bad about this.

There are plenty of videos online about how to replace the head gasket and also inspect the head. The worst case is that you will need a new head.
 
As stated above, that is oil cooked onto the head. If it is above the exhaust port, that is all it is. If it is on a part of the head where there is no exhaust port under it, it could be gasses leaking thru a valve guide. Below is a "burnt exhaust valve" where the gases leaking past it eroded it. Make sure your cooling fins are clean, don't push it to its limit especially in hot weather, and try to use non-ethanol fuels. It could also have a head gasket leaking as Auto Doc's suggested for one possibility.

Burned-valve.webp
 
Last edited:
adjusted the valves the engine starts now but the is an after fire via the muffler, can not remember what this sign indicates, have not done a pressure leak down test,
thanks
 
Is the "after fire" happen when you shut down and the engine is hot?

If so, that means the fuel solenoid on the float bowl is not closing off the fuel flow. That is the most common problem.

The solenoid pintle usually gets sticky from old fuel and additive that breaks down in the fuel.

Most of the time it is a matter of taking the solenoid off and cleaning it good with carburetor spray, then working the pintle by hand and spray it again. Be careful because some pintles come out and there is a tiny wound spring down inside that you don't want to lose.

For what it is worth, I usually put a manual shutoff in the fuel supply line and turn it off to run the carburetor out of fuel.

Those fuel solenoids create a lot of headaches especially in older machines. Aftermarket ones don't work half the time and the OEM ones are $$ big money.
 
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