String Trimmer Woes

[dennis]

Have an old Homelite UT20680 string trimmer. It starts right up, runs well for a couple of minutes, then rpms go down, up, down, up, down,up for about a minute, then it runs really well. Cleaned carb, new fuel filter, new spark plug. What can be causing this?

[KE4AVB]

To me it sounds like an air leak.

Make sure the cylinder to crankcase gasket is good and that the cylinder bolts are tight along with the carburetor heat dam (intake manifold) bolts. This model feeds the impulse port through the cylinder gasket and it very thin in that area. Also pressure/vac the crankcase for air leaks especially the crankshaft seal and crankcase cover.

[Merkava_4]

This may be a bit premature, but if you decide to replace the trimmer, I recommend the STIHL FS 91 R.

I got one a couple of weeks ago and I likes it. It has fully accessible Low and High speed mixture screws.