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Fs90r wont take throttle

#1

Gramp75

Gramp75

IAdjusting jets no help it runs starts but wont take throttle. Valve lash looks good. Right now im running bare carb covers and air cleaner missing. Opened carb all looks cleangood. Too things i noticed. Carb is spitting and when idling its rough like rich but every so often it smooths out for a second only. No idea what the bottom diaphram thing does one carb with big hose to motor? Also dont know jet settings. And whats that doohickey on top of gas tank under carb?

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#2

Hammermechanicman

Hammermechanicman

Have you checked the exhaust screen?
The doohickey is the tank vent.


#3

Gramp75

Gramp75

Hammermechanicman said:
Have you checked the exhaust screen?
The doohickey is the tank vent.
Click to expand...
It runs shoots smoke out exhaust. Th priblem i think is the gas spitting outcarb at idle. Idle is consistant but acts like every other spark fire. Other thing is jets dont effect it but carb is clean inside


#4

StarTech

StarTech

First you should not be able to adjust much with the limiter caps in place. How is the metering diaphragm? Is it stiff?

Also have you adjusted the valves? And have you checked the spark arrester?
1654206648909.png


#5

S

slomo

Pull the muffler. Clean out the exhaust port and muffler screen as suggested previously. Rebuild the carb.


#6

Gramp75

Gramp75

I see no comments about carb spitting has to be valve timing or valve fault. Like worn guide? Or cam shaft defect? I may pull muffler for kicks. Who knows? Gaskets diaphrams are good. This unit looks like its got a million miles on it.


#7

S

slomo

Gramp75 said:
I see no comments about carb spitting has to be valve timing or valve fault. Like worn guide? Or cam shaft defect? I may pull muffler for kicks. Who knows? Gaskets diaphrams are good. This unit looks like its got a million miles on it.
Click to expand...
You know this is a 2 stroke trimmer right? Doesn't have valves and such?

There is a RECALL on this trimmer. Read about it below.


1654278530375.png


#8

StarTech

StarTech

slomo said:
You know this is a 2 stroke trimmer right? Doesn't have valves and such?

There is a RECALL on this trimmer. Read about it below.


View attachment 60761
Click to expand...
Slomo, you are simply wrong as this is a 4mix trimmer engine. Just because it uses 2 cycle fuel does not mean it is a 2 cycle engine. It is a 4180 engine. See items 2 thru 5 in the following snippet and how the valves are adjusted.
1654279611143.png1654279800425.png


#9

Hammermechanicman

Hammermechanicman

If it is spitting back fuel at idle the first thing to check is the exhaust screen being plugged. On a 4 mix the next thing is valve adjustment. If engine has a lot of hours on it and not run hard enough to keep it up to temp it can be carboned up to the point intake valve not sealing properly. Stihl sells an expensive can of stuff that will decarbon an engine.


#10

Gramp75

Gramp75

slomo said:
You know this is a 2 stroke trimmer right? Doesn't have valves and such?

There is a RECALL on this trimmer. Read about it below.


View attachment 60761
Click to expand...
Actually no its a 4 stroke took balve cover off to inspect rockers/clearances


#11

S

slomo

Gramp75 said:
Actually no its a 4 stroke took balve cover off to inspect rockers/clearances
Click to expand...
I stand corrected. Model number sounded like a 2 stroke.


#12

Hammermechanicman

Hammermechanicman

It is not exactly a conventional 4 stroke engine. It is a hybrid 4 mix engine. It uses primary compression of the crankcase like a 2 stroke. That is why it needs mixed fuel to lubricate the crank, cylinder and piston. You troubleshoot these a little different than conventional 2 or 4 stroke engines. The first thing you always need to do is check the spark arrestor and the valve clearances and that the rocker cover is sealed tight. If the rocker cover is not sealed it loses primary crankcase compression.


#13

S

slomo

Hammermechanicman said:
It is not exactly a conventional 4 stroke engine. It is a hybrid 4 mix engine. It uses primary compression of the crankcase like a 2 stroke. That is why it needs mixed fuel to lubricate the crank, cylinder and piston. You troubleshoot these a little different than conventional 2 or 4 stroke engines. The first thing you always need to do is check the spark arrestor and the valve clearances and that the rocker cover is sealed tight. If the rocker cover is not sealed it loses primary crankcase compression.
Click to expand...
Wow, I had no clue. Thanks for the engine info.


#14

Gramp75

Gramp75

In that case i suppose valves could get carboned up?


#15

Fish

Fish

Here is a tech bulletin on carbon.

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  • decarbon.pdf
    138.6 KB · Views: 6


#16

S

slomo

Probably Techron in a bottle.


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