Have a stihl trimmer model FS 250 R.
Cannot get it started . Has not been used for months. When pumping primer bulb, fuel not getting to carb . Thought that maybe fuel lines to primer bulb might be wrong . Tried both orientations and found by swithing them , the fuel will dispense into the carb. Tried putting fuel into spark plug hole, and this still would not fire. Also tried carb cleaner with no luck. I am using clean gas mixture
that you buy in a can( premixed 50 to 1). Since it would not fire with fuel in the spark plug hole. I suspect that I am not getting ignition, but with this model , I do not know how to test it for sparks . I know the method of using a screw driver
held to ground and watching for spark at the gap of the screw driver blade close to the end of the spark plug, but where is ground on this model??

 

Ground is a metal part of the engine (cylinder works well).

 

Tested ignition wire for spark with a TRU-SPARK IGNITION FIRING INDICATOR. shows good spark.
This was with spark plug out. When spark plug was put back in. it did not fire, even I squirted carb cleaner in both the carb and spark plug chambers. What now ??

 

also put in new spark plug

 

Been thinking about it more. Since I have spark at the plug wire and not at the plug, I suspect the spark plug ignition wire may have an open. I know I have taken off the spark plug often and the spark plug wire is very short and was flexed often by the spark plug wrench. The shop is closed now , but I will check this next. What is yoyr opinion ??

 

stihl model fs250R, how do I check to see if the switch is working. I see it has a micro switch with wires going to the handle.
Can you give me a view diagram on the positioning of the spring that activates the throttle trigger interlock

 

If you have an ohmmeter, you test for continuity across the switch with it switched off, and open circuit with it on. If you have spark at the plug wire, the switch is not causing your problem. Have you checked yet to see if the spark plug itself is actually firing or not? How do you know it's not firing when you install it?