Stihl trimmer won't idle and flooding?

[38racing]

My neighbour's passed his cousin my way having problem with stihl pro series curved shaft trimmer. I'm led to believe it ran ok until he put a heavy wire head on it to do weeds in paver stone driveway. He said it would run on high speed but not idle. He admitted to turning carb screws after idle failed. I figured maybe it needed higher idle speed to maintain enough power to the heavier head. I agreed to look at it. I adjusted mixture screws as per label. 3/4 for h and 1 for low. Also turned idle speed clockwise a turn. It has part throttle lock position for starting. I got it started and pulled trigger to high and turning speed in slightly gets high smooth operation. If I release trigger it stops and won't restart. If it sits for awhile it will start without prime or choke but exactly same thing happens. Release trigger and it stops and no start. Various settings of low mix changes nothing. I asked him to bring regular head so I could try tuning it with it on. At that point i learned that he had changed coil and plug but it apparently ran. I put on regular head but also gapped both coil and plug. Exactly same issues. Now I did feel gas when I primed it once so maybe bulb is bad. My sense is that its flooding. That's why it stalls on low speed and won't start until it sits long enough for plug to dry. I could suggest maybe he would want to risk a $25 aftermarket carb or I can suggest he take to a dealer to test other things that might be causing this. Any thoughts?

[KE4AVB]

38, You should know by now that we need the equipment info. I do have most of the Stihl service manuals and those that I don't I can get within a few days.

As the those tuning that is if the EPA limiters are still on the carburetor and lock down after the last Stihl tech serviced the trimmer. I can snip and post the tuning instructions once I know what you have.

[RoyM]

Give him heck, he knows better.

[38racing]

Fs75

[KE4AVB]

The images of the carb adjustment pages are rather large so I convert to a two page PDF.

https://1drv.ms/b/s!AhP6VW6j_ZC5i2q2CYupxwyZBHu0?e=VheASm

NOTE: max engine no load speed is 10,500 rpm with an idle speed of 2800 rpm. Plus this unit does have a clutch so if the head is still spinning at idle either the idle speed is too high or the clutch has a failure. Springs are known to break.

As for the possible flooding check the metering diaphragm, lever height, and needle valve. Also don't forget to check the spark arrester screen.

If you PM me your email address I can send you a couple links to the SM and IPL. Just don't want Stihl crawling me for having them since they are dealer only items.

Just no telling what carburetor Stihl now has for this unit, changes over time.

[38racing]

Thanks. Says 1 turn and 2 turns on the document. Carb is labeled 3/4 and 1. Am I correct that even though low can be turned multiple turns do the black covers need to be popped to get the needles to the closed position? I'm not inclined to really go beyond seeing if it's just out of adjustment on this one.

[KE4AVB]

Sound you a carburetor with a fully adjustable low speed. But they are true limiter caps they must be cut off or otherwise removed in order to seat the mixture screws. Stihl does have a tool for pry them off. The caps can't be reused.

That label for carbs that have limiter caps installed which is the limit of their range. Depending the model some those mixture are turn as much as three turns out from seat position but they are still label as you described when the caps are in place.

[38racing]

Saw a video of a guy popping them off with a screwdriver. May try that.

[38racing]

Cap on low did not limit but one on high did. Owner was willing to gamble 30$ on a carb. Got one from Amazon and it's running. How critical is the fuel mixture? I'm thinking that I'll have him drop off his fuel can for the final tuning with his wire head on it.

[KE4AVB]

Warm up the engine first.

Max. permissible engine speed without cutting blades (cut-off speed): 10500 rpm(+ 000 rpm)
Max. speed of the output shaft (nominal value, gear head): 8500 rpm(FS 75, FC 75) 7500 rpm(FS 80, 85)
Tune to max RPM not to exceed 10500 and then enrich by 50 rpm drop.

But first tune the idle speed.

Idle speed: 2800 rpm
Tune at 3600 rpm for max idle rpm and drop to 2800 using LA