Changes in engine
speed can be due to several things. You said it goes "faster and faster". I assume you don't mean it assumes a "runaway condition" wherein it will just keep accelerating at very high rpms. That could be due to a malfunctioning governor and/or other problems.
Assuming you mean it runs faster, then slows down, then faster....i.e., appears to "hunt", I'd consider the fuel
system first. Could be due to poor or contaminated fuel
, clogged fuel filters, air getting into the fuel lines, etc. Sometimes these problems are simple to fix; sometimes they're the very devil.
Years ago I had a problem on my Perkins
4-108 which was driving me crazy. Finally tracked it down to a pinhole in the bottom
of a copper fuel line running in the bilge
-- out of sight. Found it only by sound (hissing when the manual fuel lever was pumped) and by touch.
Recently, after many years of no such troubles, I had another "hunting" problem with my Perkins. Every two to three minutes when at 2300rpm cruising speed, the engine
would speed up a few hundred rpm
, then drop back within a few seconds. Tracked that one down to loose connections on the on-engine fuel filter
. Easy fix :-)