--- In ppgbiglist@yahoogroups.com, "keithbenitez" <keithbenitez@...> wrote:
>
> I am having a problem with my Blackdevil 172 engine. I turn it on and it runs
great for about 4 minutes or so, then slowly the RPMs drop. It starts off at a
nice powerful 7600RPM then it goes down to eventually 6600RPM. If I let it go
back to idle and then go back to full throttle I can get it to go to maybe
7400RPM but again it just continues to drop.

Check fuel tank breather is adequate, and that you aren't gradually building up
an ever increasing vacuum when at full revs, which then resolves at lower revs
due to lower fuel flow.

Other than that, it could as others have suggested be a smidge (technical term)
lean, with the result that the engine is getting a bit close to nipping up when
it gets really hot.

Just a though