Specifications

25MS 290, MS 310, MS 390
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 engine housing can be checked
thoroughly for leaks with the
carburetor and crankcase tester
and the vacuum pump, b 11.2.2
– Remove the muffler, b 6.1
: Fit the sealing plate (1)
0000 855 8106 between the
mounting screws.
The sealing plate must completely
fill the space between the two
VA
209RA026
1
2
3
4
mounting screws.
: Slip the flange (2) 1123 855 4200
over the screws.
: Fit the sleeves (3) 1123 851 8300
on the screws.
: Fit the nuts (4) and tighten down
securely, b 3.5
– Remove the carburetor,
b 11.2.1
– Set the piston to top dead center
(T.D.C.). This can be checked
through the inlet port.
: Check that the sleeve (1) and
washer (2) are properly seated.
VA
209RA027
2
1
: Check that the pin (1) in test
flange 1128 850 4200 is in hole
No. 1 (arrow), or fit if necessary.
VA
176RA017
1
: Fit the test flange (1).
: Tighten down the screws (2)
firmly, b 3.5
– Check that spark plug is properly
tightened down.
VA
209RA028
1
2 3
4
– Pressure test, b 6.2.2
– Vacuum test, b 6.2.3
When fitting the test flange, make
sure the pin (3) locates properly in
the impulse hose (4).
6.2 Leakage Test 6.2.1 Preparations