27Series 4180 Powerhead
All models
: Place the new limiter caps on the 
screws (1 and 2) so they are 
positioned against the rich stop 
(arrow)
2
1
: Push limiter caps onto the screws 
to the second noticeable stop 
(until dimension “a” is 5 mm).
Limiter caps must not butt against 
the carburetor body.
 
– Adjust engine idle speed, b
6.4
Correct operation of the carburetor 
is only possible if atmospheric 
pressure and internal fuel tank 
pressure are equal at all times. This 
is ensured by the tank vent.
In the case of problems with the 
carburetor or fuel supply system, 
also check the tank vent. 
There are two types of tank vents:
: Tank vent (A) without return line.
: Tank vent (B) with connection to 
return line on the clean air side of 
the air filter.
: Only tank vent (A) without return 
line may be installed in fuel tanks 
with a 2.2 mm shoulder (a).
: A tank vent with return line (B) 
may be installed or retrofitted in 
fuel tanks with a 5.2 mm shoulder 
(a).
Check function of tank vent by 
carrying out vacuum test on fuel 
tank via the fuel hoses.
To do this:
– Drain the fuel tank, b
6.6.1
: Pull both fuel hoses (1 and 2) off 
the carburetor.
– Use a suitable plug to seal the 
fuel hose (1). 
2
1
6.5 Tank Vent
6.5.1 Checking Operation