FS90R 4 mix woes

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FlyingDutchman

Not again...
AS Supporting Member.
Joined
Apr 25, 2009
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Location
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Been having trouble with my my FS90R for a couple years now.
It dies at idle, is hard to start and doesn't like to idle down/disengage clutch. I have to crank the idle past clutch engagement so it doesn't die. Sometimes it acts like it is missing and has no power. A tune up kit helped it somewhat a few years ago with dying. The primer bulb is and always has been very, very stiff and always has some air in it. All my other Stihl equipment, the primer pushes easily and lots of times all the air comes out.
A couple weeks ago, I replaced the primer bulb after it broke, and adjusted the valves to spec, adjusted the carb to factory. It fired right up and ran excellent for one or two tanks. I ran it out of fuel yesterday. Put the next tank in and it went back to hell in a handbasket or worse, flooding out instead of running. Double checked the valve cover was tight and spark is extremely strong. Will jump an inch to the motor case.
Takes 20 pulls to get it restarted after shutting off last night, extremely frustrating.
Its possible it got a snoot full of bad fuel, but other equipment seems to run okay on that fuel.
Do these have an inlet screen on the carb?
Do they fall out of adjustment after adjusted?
Time to trade for a Kombi?
 
What do you mean by stripping carbs? Rebuilding them?
Last night it would only run if I pushed the primer bulb, but totally stopped running when i took the fuel filter off. I did have trouble with that same fuel running in other equipment, so I'm going to try some different fuel before swapping the carb. Been using this machine every day so I'd probably just stuff an OEM on it.
 
FlyingDutchman said:
What do you mean by stripping carbs? Rebuilding them?
Last night it would only run if I pushed the primer bulb, but totally stopped running when i took the fuel filter off. I did have trouble with that same fuel running in other equipment, so I'm going to try some different fuel before swapping the carb. Been using this machine every day so I'd probably just stuff an OEM on it.
Click to expand...
stripping them down and ultrasonic clean + airline blowing the jets out
it fixes them sometimes, but swapping the carb is easier, and the copy ones are fully adjustable too
oem pistons etc, but stihl carbs are chinese anyway
 
frank_ said:
swapping the carb is easier, and the copy ones are fully adjustable too
Click to expand...
Great plan, until you run into a bad batch of China carbs. Then you're just another "how come my Chinese **** doesn't work and how come they won't help me replace it" thread starter. If you're going to be fooling with small engines, learning how to re-build a carburetor is Day 1 stuff...
 
In Frank's defense, the Stihl dealer I work with said the exact same thing. Replace vs rebuild. Worked like a charm for m FS45. The FS90 has a more expensive carb so it might be worth rebuilding he said, but he said "every time I rebuild one it just seems to bite me in the ass. Replacing works every time." I just don't understand why it would run so well then not at all.

Not looking forward to checking valves again but okay. Thanks Angelo.
 
1. Drained fuel. Purged lines.
2. Install new fuel. Purge lines.
3. Remove engine cover.
4. Remove valve cover.
5. Set engine to TDC.
6. Reset valves to .004. They were a bit too tight before Now it feels like it has more compression when pulled over.
7. Install valve cover, engine cover.
8. Won't start at all. Pulled plug, dried, reinstall. No go.
9. Get mad, go to dealership and buy a carb.
10. Come home. Pull one more time BEFORE putting on carb. Fires up like nothing ever happened runs fine starting on 1-2 pulls.
11. Go insane.
 
N\
FlyingDutchman said:
1. Drained fuel. Purged lines.
2. Install new fuel. Purge lines.
3. Remove engine cover.
4. Remove valve cover.
5. Set engine to TDC.
6. Reset valves to .004. They were a bit too tight before Now it feels like it has more compression when pulled over.
7. Install valve cover, engine cover.
8. Won't start at all. Pulled plug, dried, reinstall. No go.
9. Get mad, go to dealership and buy a carb.
10. Come home. Pull one more time BEFORE putting on carb. Fires up like nothing ever happened runs fine starting on 1-2 pulls.
11. Go insane.
Click to expand...
Thats when you buy a new one.
 
FlyingDutchman said:
1. Drained fuel. Purged lines.
2. Install new fuel. Purge lines.
3. Remove engine cover.
4. Remove valve cover.
5. Set engine to TDC.
6. Reset valves to .004. They were a bit too tight before Now it feels like it has more compression when pulled over.
7. Install valve cover, engine cover.
8. Won't start at all. Pulled plug, dried, reinstall. No go.
9. Get mad, go to dealership and buy a carb.
10. Come home. Pull one more time BEFORE putting on carb. Fires up like nothing ever happened runs fine starting on 1-2 pulls.
11. Go insane.
Click to expand...

Told ya it was the valves.... :)
J/k
 
had one in today with the same hard start and crap idle issues, the valve adjustment was scattering from 5 to 20" thou if you turned it forwards or backwards
it proved to be the hole in the casing that had worn badly oval, letting the cam follower shaft to move up and down
so we drilled the hole out and rammed some alloy tubing in :)

IMG_1402.pngWP_20141130_05_04_40_Pro.jpg
 
FlyingDutchman said:
1. Drained fuel. Purged lines.
2. Install new fuel. Purge lines.
3. Remove engine cover.
4. Remove valve cover.
5. Set engine to TDC.
6. Reset valves to .004. They were a bit too tight before Now it feels like it has more compression when pulled over.
7. Install valve cover, engine cover.
8. Won't start at all. Pulled plug, dried, reinstall. No go.
9. Get mad, go to dealership and buy a carb.
10. Come home. Pull one more time BEFORE putting on carb. Fires up like nothing ever happened runs fine starting on 1-2 pulls.
11. Go insane.
Click to expand...
Just adding for anyone following along on adjusting the valves...
There's 2 TDC on these guys..
One where the valves jiggle if you move the flywheel back.and forth and another where the valve don't move if you slightly rock the flywheel. You want the TDC that does NOT move the valves when the flywheel is Slightly rocked.
 
angelo c said:
Just adding for anyone following along on adjusting the valves...
There's 2 TDC on these guys..
One where the valves jiggle if you move the flywheel back.and forth and another where the valve don't move if you slightly rock the flywheel. You want the TDC that does NOT move the valves when the flywheel is Slightly rocked.
Click to expand...
Are you sure about that?
 

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