Stihl FS 75full throttle issue

[jwales]

friend cleaning out his dads garage and dropped off 2 Stihl FS 75 curved shaft trimmers and wanted me to see if I could get them running,(or at least one). Both looked to be complete and in good condition on the surface. fuel lines were brittle. So I have pulled the carbs separately,disassembled and run through USC several times each. Replaced fuel and primer lines. new spark plugs and cleaned the muffler screen/spark arrestor. They have good spark and good compression.
One fires right up and idles like a dream. add full throttle and it stops. Can get it to full throttle f Iplay with choke while trying. Then Seems to run at full throttle fine. Besides idle it only has one adjustment. I believe it is lo speed adjustment as nothing happens when running at full throttle and adjusting it. Am I looking at a plugged fuel passage still? Id there something else I should be checking? Thanks.

Two fires and idles for 45 seconds then stops as if fuel starved. I have been able to get it to full speed playing with the throttle and no choke, and it runs wide open ok. I have been trying to adjust the lo speed adjustment before it stops to see if it will idle on its own. Not successful. Again, any thoughts other/in addition to pulling carb again and running through USC some more?

The gaskets, needle and metering lever seem OK (not torn/visibly damaged) so I reused them.

Thanks for your ideas.

[RoyM]

Replace the diaphragms and gaskets, they are probably hardened from old age like me.

[KE4AVB]

Also replace the fuel filter and check/replace the carburetor's internal filter screen. Old filters depending construction will shed grey stuff and clog the internal filter.

[38racing]

Also replace the fuel filter and check/replace the carburetor's internal filter screen. Old filters depending construction will shed grey stuff and clog the internal filter.

I just cleaned those 2 zamas. One had intake filter fine yet internal screen was plugged solid with gritty material. The other one has gray guck in tank and on filter and even in outlet nipple of filter. Internal screen just a bit of debris.

[38racing]

I guess carbs may vary but the fs 75 that I recently replaced carb for 25 cdn had both low and high speed mixture adjustment on original and replacement.

[KE4AVB]

I guess carbs may vary but the fs 75 that I recently replaced carb for 25 cdn had both low and high speed mixture adjustment on original and replacement.

You luck dog...Of the last ten cube carbs I order in after market only one worked, the others had to be sent back for credit and new ones purchased from the local Stihl dealer.

[jwales]

I should have looked closer at 38’s posts! One is working good. Will get a kit for the other. It is a Samantha with C10 stamped I one area and I think S41A in another with 825B below it. Any idea on kit replacement part number?

[KE4AVB]

That would be a C1Q-S41A. Then Zama Carburetor kit is RB-85 if you can find one or Stihl PN 0000 007 1089. I got one Zama kit left then I would to get them thru CTS myself.

OR if you got plenty of time you get them thru CTS