Stihl MS 390 User Manual

7MS 290, MS 310, MS 390
4. Troubleshooting Chart
4.1 Clutch, Chain Drive, Chain Brake,
Chain Tensioner
Condition Cause Remedy
Saw chain stops under load at full
throttle
Clutch shoes badly worn Install new clutch
Clutch drum badly worn Install new clutch drum
Brake band stuck Check freedom of movement
and function of brake band
Saw chain rotates at idle speed Engine idle speed too high Readjust with idle speed screw
(LA) (counterclockwise)
Clutch springs stretched or fatigued Replace the clutch springs, or
clutch if necessary
Clutch spring hooks broken Replace the clutch springs
Loud noises Clutch springs stretched or fatigued Replace all clutch springs
Needle cage damaged Fit new needle cage
Clutch shoe retainer broken Fit new retainer
Clutch shoes and carrier worn Install new clutch
Chain sprocket wears rapidly Chain not properly tensioned Tension chain as specified
Wrong chain pitch Fit chain of correct pitch
Insufficient chain lubrication Check chain lubrication
Chain sprocket worn Install new chain sprocket
Chain does not stop immediately
when brake is activated
Brake spring stretched or broken Fit new brake spring
Brake band stretched / worn /
broken
Fit new brake band
Clutch drum worn Install new clutch drum

Stihl MS 390 Specifications

General

Engine Displacement	64.1 cc
Chain Pitch	3/8"
Weight	6.2 kg
Guide Bar Lengths	40 to 50 cm
Fuel Capacity	0.68 l (23.0 oz)