• Please be aware that we have recently gotten a wave of users that, when researched, are found to be from Nigeria. They are trying to sell products and asking to be paid through Zelle or Venmo leaving users with no recourse if they don't ship the product. If you suspect this activity please contact admin and we will research their information to verify their location.

ArboristSite.com Sponsors
www.harvesterbars.com


Stihl FS-38 trimmer mystery!!!!!!!!!

goosemaster

goosemaster

ArboristSite Operative
Joined
Aug 28, 2016
Messages
139
Age
64
Location
Kentucky
Yeah I believe I'm going to try and get a leak down test done on it. What gets me about the whole thing is; I've always been able to get one to hit using a small shot of starting fluid. Not this one. Nothing.
 
fowvay

fowvay

New Member
Joined
Jul 15, 2020
Messages
2
Location
Georgia
If you got no results with ether then you have a compression issue. While you had the engine disassembled I hope you cleaned the ring groove and checked the ring gap. Also, be certain the purge circuit on the carburetor is functioning to ensure fuel is in the carburetor. Please let us know what you determine. I recently brought an FS-38 back from the dead for a neighbor but their only issue was with old fuel and dirty carburetor.
 
stihl86

stihl86

ArboristSite Guru
Joined
Jul 27, 2008
Messages
746
Location
Northeast
1) A leakdown test and a Vac/Pressure test are two completely different tests.
IF the dealer will/can do a Vac/pressure test, the intake manifold must be on.
2) Most modern 2 cycles have a variable ign timing circuity. It adds in reduced starting effort. If that portion of the module is defective, and they do fail, you'll never get it stated. It might be sparking at the wrong time. That would explain the backfiring. The timing is separate from the magneto portion, meaning it will show good spark.

I will get you credit for you vigilance in trying to get it running.
You already have, in labor and parts well over what the trimmer is/was worth.
On its best day.
 
Okie294life

Okie294life

Small engine jackwagen.
Joined
Jun 25, 2018
Messages
352
Age
42
Location
Arkansas
1) A leakdown test and a Vac/Pressure test are two completely different tests.
IF the dealer will/can do a Vac/pressure test, the intake manifold must be on.
2) Most modern 2 cycles have a variable ign timing circuity. It adds in reduced starting effort. If that portion of the module is defective, and they do fail, you'll never get it stated. It might be sparking at the wrong time. That would explain the backfiring. The timing is separate from the magneto portion, meaning it will show good spark.

I will get you credit for you vigilance in trying to get it running.
You already have, in labor and parts well over what the trimmer is/was worth.
On its best day.
Did you gap the coil when you put it back on? I usually use two sheets of paper or an envelope if I can find one.
 
Ax-man

Ax-man

Addicted to ArboristSite
Joined
Jul 28, 2003
Messages
2,426
Age
65
Location
NE Illinois
Maybe your new coil and flywheel aren't compatible and spark is occurring at the wrong part of the cycle. Two things would happen if this is the case , big time flooding or the pull start would get jerked out your hand or be very hard to pull over . Why did you buy a new flywheel???

If your machine isn't even try to fire starter fluid isn't going to help it will only make matters worse because it takes longer to fire an engine using starter fluid to clear the cylinder out before it does any good . Two stroke mix is the best for obvious reasons.
 
Top