FS90 four mix powerhead?

[67L36Driver]

This thing has me stumped.

The valves checked good and the piston/rings/cylinder are pristine. [emoji108]

Yet it only pumps 50 psi because it has a compression release??

How does that work?

I’ve gotten it to run along dismally a couple of times but dies after ten fifteen seconds.

Resorted to spinning it over with a drill motor but no joy.

 

[angelo c]

Sometimes the "decompression" spring on the cam warbles stuck and wallah...take it apart and check the plastic cam follower. Very simple engines. Usually the valves or the cam...post back with followings.

 

[67L36Driver]

Sometimes the "decompression" spring on the cam warbles stuck and wallah...take it apart and check the plastic cam follower. Very simple engines. Usually the valves or the cam...post back with followings.

Can one just delete that feature?

Really? A compression release on a 28cc engine?

Damn krauts!

 

[angelo c]

Nope. Yer 9 year old daughter will thank you when she needs to blow rocks off her favorite doll house...

 

[67L36Driver]

Deleted the ‘cam bump thingy’ and spring.

Now it starts much more reliably but the carb (damn Zama to hell !!) isn’t at a happy place.

 

[67L36Driver]

The culprit:

Discarded this:

Had to make this to adjust the valve lash:

.003” brass shim stock. Made a two-fer. The narrow one worked. [emoji108]

Cant get the Zama to pass fuel. Buy a replacement off evilbay, we will.

 

[angelo c]

Does your 9 year old approve of how her elbow feels after the new "vigorous " start process

 

[67L36Driver]

No nine yo here. Daughter is 41 and granddaughter is sixteen and bigger. [emoji2960]


Sent from my iPhone using Tapatalk

 

[67L36Driver]

Revisiting this FS90 turd:

Defeated the compression release and checked comp. I now have a 10mm adaptor for my gauge now.

Is 90 psi normal for a four mix engine?

The valves may be not so good after all. [emoji90]

 

[67L36Driver]

John at Jack Horners Supply did a leak down test for me.

All is good with valve and ring seal. [emoji108]

It’s got fat spark so the issue is fuel or possibly spark timing.

 

[ray benson]

Revisiting this FS90 turd:

Defeated the compression release and checked comp. I now have a 10mm adaptor for my gauge now.

Is 90 psi normal for a four mix engine?

The valves may be not so good after all. [emoji90]

Manual says 6 to 7 bar (87 to 101 psi) the design specification.

If the compression pressure is below 6 bar, check valve clearance and readjust if necessary. If this produces no improvement, check the cylinder, valve seat, piston and piston rings for scores or other damage. The design specification is 6...7 bar.

 

[67L36Driver]

Can someone tell me where to set the high and low mixture screws?

I can get it to start but it starves out for fuel and dies.

At least I think it’s a fuel issue. [emoji848]

 

[DND 9000]

Depends on the carburetor you have. Model description?

 

[67L36Driver]

Zama C1Q
S174
4180/11A
805A

 

[DND 9000]

Basic setting:

L=1 1/2
H=3 1/2

 

[67L36Driver]

Basic setting:

L=1 1/2
H=3 1/2

High at 3 1/2. Yikes!

I’ll give it a go. [emoji1696]

 

[67L36Driver]

Broke down and had the dealer fix it.

The original carb was plugged up and the China copy was junk.

A new Stihl carb and, most importantly, a new fuel tank pick up hose solved the problem.

$125 brought our four mix education to a finish.

With this on the end, we have us a shorty pole saw. [emoji108]