When runninng i cant engage the off switch

There are several conditions and situations that this can occur, but let's try the most common. This is also for any STIHL saw that was manufactured before 2014, after that, the M-Tronic saws have a different starting method.
Normally this happens when the engine fired and it was not audible, and the rope has continued to be pulled with the choke on.
This method is approved, but EXTREME caution should be used, and the CHAIN BRAKE must be used.
CAUTION: Do NOT use the drop start method, this is not an approved starting method under any circumstance!
1) Place the saw on the ground that is clear of debris.
2) Set the Chain Brake
b) place the toe of your right shoe thru the rear handle,
c) support the saw top handle with your left hand,
d) pull the recoil with your right hand.
3) Make sure the choke is NOT applied, place the master control lever in the start position (one notch above the choke position)
NOTE: at this point, it helps if a second person can hold the throttle at the full or wide open position.
4) Make 6 rapid pulls (a few more may be required), you should hear the saw start to sputter, keep the throttle open until enough rpm is obtained that YOU the Operator can gain control of the throttle (the other person stands aside now in a safe position) and remove the chain brake. Keep the throttle open until the saw starts to run properly.
*NOTE 2: The chain brake is designed to not only stop the chain in case of 'kick back', but also is to be used in starting the saw until you have time to gain full operational control of the saw. However, extended rpms above clutch engagement can damage the brake band, overheat the drum bearing, damage the clutch shoes and clutch drum.

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

Choke leaver worn at carby or the lock off position worn.

check the position of the safety lever /clutch as there may be a micro switch that will not allow it to start with the chain engaged

simple things first
right fuel /oil ratio in tank ?
aircleaner not blocked off with sawdust?

stop switch set to correct "run" position , switch not broken damaged ? chain brake set ?

choke set correct to start ?
primer bulb working correctly , fuel is visible inside bulb

Start by filling the fuel tank with a fresh mix of 50-1, fill the chain oil tank with non fling chain oil, sit the saw on the ground with the bar away from any obstructions, engage the chainbrake, switch the ignition on, press the fuel bulb as many times as it takes to 3/4 fill the bulb, pull the choke out, this should also engage the fast idle, crank the engine until it fires once, it will not run on choke, it is importent at this point you must push the choke back in, now crank the engine until it runs, flick the trigger to allow the saw to idle.

The chainbrake should be activated when starting the chain saw. Activate the chain brakeby pushing the front hand guard forwards.b>Cold engine Start position, 1: Set the start/stop switch in the choke position by pulling thered control outward - upward.Decompression valve: Press the valve to reduce the pressure in the cylinder and makestarting easier. Once the machine has started the valve will automaticallyreturn to its original setting.Air purge: Press the air purge diaphragm repeatedly until fuel fills thediaphragm (at least 6 times). The diaphragm need not be completely filled.Grip the front handle with yourleft hand. Hold the chain saw on the ground by placing your right foot throughthe rear handle.Pull the starter handle, 4: Pull the starter handle with your right hand and pull out thestarter cord slowly until you feel a resistance (as the starter pawls engage)then pull firmly and rapidly until the engine fires.Push down the red choke control: As soon as the engine fires which can be heard through a"puff" sound, push down on the red choke control.Pull the starter handle (6): Keep on pulling the cord powerfully until the engine starts.

Mine did the same thing. Take off the cylinder cover as described above. Take off the screw holding the on/off switch. <br /> Bend the bottom of the silver metal shutoff band down where it rides against the back of the switch. Bend until switch turns on and off smoothly.<!-- from fixya rte -->

First the chain should be tightened properly before starting. When you pick up on the chain midway of the bar it should pull away from the bar about 1/4". The proper mix of oil & gas in the fuel tank & Oil for the chain in the oiler tankk is needed, If so, locate the on/off switch & turn it to "on". Pull the choke lever out. Depress the throttle trigger & engage the latch for the trigger. With the saw held firmly in place, pull the starter rope until the engine hits. Then move the choke to half & pull till it cranks. move the choke lever to the run position.

I didn't know that chain saws had fuses? The black handle you are talking about is a chain break, push it forward allows the chain to drive, if chain break is back chain will not run around the bar, safety for saw kick backs.
If it will not start:
Check and see if it has fuel.
Is the switch in the on Position?
Do you have a fowl plug? is there spark?
Is the plug wire attached correctly?
Do you have fuel going to the carb?
Is your air cleaner, clean?
DO you smell gas, if so you have probably flooded it and now you will have to remove the spark plug and get rid of excess fuel or try starting the saw with the choke on.

Been a while since I saw a Jonsered but I think if you bend the choke linkage a little that it will stay in the choke position.