Leakage Test; Preparations - Stihl MS 650 Manual

6.3

Leakage Test

Defective oil seals and gaskets or
cracks in castings are the usual
causes of leaks. Such faults allow
supplementary air to enter the
engine and upset the fuel-air
mixture.
This makes adjustment of the
prescribed idle speed difficult, if not
impossible.
Moreover, the transition from idle
speed to part or full throttle is not
smooth.
The crankcase can be checked
thoroughly for leaks with the
carburetor and crankcase tester
and the vacuum pump.
For systematic troubleshooting,
always perform the vacuum test first
and then the pressure test.
30
6.3.1

Preparations

2
– Remove the shroud – b 6.2
– Remove the decompression
valve – b 6.8
: Install plug (1) 1122 025 2200
and tighten down to 25 Nm.
: Fit spark plug (2) and tighten it
down firmly – b 3.5
– Remove muffler top casing –
b 6.1.
: Back off the bottom casing
screws (arrows) half way –
b 6.1
1
: Fit the sealing plate (1)
0000 855 8106 between the
muffler and cylinder exhaust port
and tighten down the screws
moderately.
The sealing plate must completely
fill the space between the two
screws.
– Remove the carburetor –
b 12.2.1
– Set the piston to top dead center.
This can be checked through the
inlet port.
1
: Check that the sleeve (1) and
washer (2) are in place.
1
2
MS 650, MS 660