FS90 4-mix carb tuning

[Mad Professor]

Helping my cousin with his FS90.

Never tuned carb on 4-mix motors. What is correct way to set Hi/Lo on these? Have done many 2-stroke chainsaws "by ear".

Also cover shows 3/4 out for both Hi/Lo. But..... the Settings were 3 1/2 Hi , 1 1/4 Lo.

Another thread mentions this/these changes :
"

How on earth do I tune the carb on one of these 4 mix engins? I had to slap a new carb on and now have no baseline for carb settings.

"There is an old FS90 and a newer FS90. Newer initial settings
FS 90; FC 90, 95; KM 90 (C1Q-S110) – Open the high speed screw H 3 1/2 turns counterclockwise. – Open the low speed screw L 1 1/4 turns counterclockwise."

https://www.arboristsite.com/threads/stihl-fs-90.368963/#post-8056214

Any advice on this?

Will be going to "Beg for Manuals" next.

 

[SCMtnHaul]

I have not swapped a carb on a 4mix but I do know they sound different than a 2 stroke. Pretty sure the 4mix have an RPM limiter and WOT sounds different. I have actually been in my local repair shop when a guy brought in a 4mix because it sounded like it needed a tuneup. Even when the tech tried to explain the difference the guy insisted there was a problem. Oh well, some people. . .