Stihl FS-55 Valve Adjustment

[Buckeyeman]

They can but I would first look to verify there are leaks between carb and intake and that there are no other vacuum leaks into the crankcase. Any leaks in crankcase will cause 2 stroke to run lean and be hard starting.

Is plug getting wet when doesn’t start?

Like others have stated also confirm good spark or just replace plug, check to verify exhaust spark arrestor is bot plugged.

I did a compression check, and it was 95. Not sure what the spec is though. I removed the exhaust pipe, and there is no screen. Since it's so old, the Stihl dealer said it didn't come with a spark arrester back then. Had to mow 2 acres today, so I haven't had time to adjust the carb. The plug is not wet.

 

[oldnslo]

When you had muffler removed could you look into the cylinder bore to see if it was scratched? Since you say is old just another thought on things to check.

95 PSI sounds like on low side but like you not sure what it should be.

Does this model have primer bulb? If yes does it fill with gas? Reason for asking is that I have gotten lines swapped and that doesn’t work very well…

Any way you can put your hand or piece of plastic across intake on carb to see what type of vacuum you are getting? Careful you don’t suck the plastic into the carb?

Was the carb from Stihl or chinese clone?

 

[ericm979]

Does the reed valve go bad?

They do sometimes. They fair to seal completely and that affects the low speed running first. But modern two stroke yard and garden type equipment usually does not have a reed valve.

 

[ericm979]

I did a compression check, and it was 95.

Was that with the throttle held open? If so, it's low. That will cause problems with low speed running and starting.

 

[dodge man]

Anything I’ve taken apart lately hasn’t had a reed valve. I like working on engines but sometimes I put up with a poor running engine out of laziness. I had a leaf blower, it was idling to slow and would die, it would also bog when opening the throttle off idle. Two minutes with a screw driver adjusting the idle speed and mixture screws and it ran great.

 

[RandyT]

The only 2 cycles that have a reed valve are 3rd port entry engines, Which translated to the carb and intake are mounting onto the lower crankcase. If the intake is on the side of the cylinder then no reed valve because the piston going up opens the intake port and gets closed when the piston goes down.

 

[tomplum]

FWIW, on the larger FS models -occasionally a weak coil will make them have a bugger of a time on a cold start.

 

[RandyT]

FWIW, on the larger FS models -occasionally a weak coil will make them have a bugger of a time on a cold start.

And in some cases the coil doesn't have to be weak. With some coils having various spark timing and included rev limiters. Makes it very difficult to determine a faulty coil when the coil never looses spark.

 

[masseyrider]

I had an FS85 and couldn't get it to run well, no way no how.
Turned out the carb and the mating surface were slightly warped and it was sucking air.
A very thin layer of appropriate silicone and it ran great for years.
Just a thought.

 

[ericm979]

The only 2 cycles that have a reed valve are 3rd port entry engines, Which translated to the carb and intake are mounting onto the lower crankcase. If the intake is on the side of the cylinder then no reed valve because the piston going up opens the intake port and gets closed when the piston goes down.

Cylinder reed valves used to be common on motorcycles. Sometimes they'd have windows in the intake skirt of the piston to increase intake duration (when the reeds allowed).

Now most have the inlet going directly to the cases.

The reeds I have seen in older small power equipment were really inefficient compared to motorcycle reed valves. But the motorcycle V shaped type take up more room. On a motorcycle that's not much of a problem but on a chainsaw or string trimmer, space and weight are the biggest factors. The piston port intake takes less space than a good reed valve. On an engine that has a limited operating rpm range (i.e full throttle all the time) the piston port can make just as much power.