On Sat, 26 Jun 2010 22:56:52 -0700 (PDT), harry
wrote:

On Jun 26, 11:22*pm, Ned Flanders
wrote:
I have a small tiller I bought second had - 4 stroke. It ran well the
first year and then it developed a small problem. I can start it (fresh
gas, clean oil), but as soon as I pull on the throttle it stalls. when
it stalls I get a little blow back out of the throat of the carburetor.
Also if I take the oil cap off while it is running there is blow back
coming out of there as well.

I am not afraid to rip it down, as I can do minor engine repairs. I was
just hoping someone might be able to point me in the right direction.

I am thinking a gasket...

It's not worth taking in for repair as the labour would cost more then
the thing is worth.

I would start with a compression test. Gases coming fom the oil cap
usually indicates worn/broken piston rings, though if it's pretty old
you can expect worn rings. It may have been siezed up in the past due
to lack of oil. & someone's succeed in freeing it off. Check the
cylinder head bolts too.
It sounds to me like there's more than one fault which could arise if
the engine is old. If you check the compression & then put a little
oil in th spark plug hole and check again and the compression is up,
that indicates a ring problem. If not. it's likely to be the valves/
head gasket problem.

Compr ession may well be bad, but my impression is that small engines
will usually run find with low compression, and the problem he needs
to fix is something else.