FS45 trimmer problem, help!!

[ryans4022]

Hello all, Im working on a stihl fs 45 trimmer. 120-130psi compression, new carb, fuel line and filter, great spark, good gas. Will pop on occasion while on choke. Its doing the same thing my fs55 did awhile back, it had alot of hours so i replaced the powerhead problem solved but this one has good everything. I dont see any scoring on the piston or cylinder. Im turning blue trying to start it!! Thanks in advance for the help! Ryan

 

[Fedaburger]

Have you tried a splash of mix down the carb yet. Everything sounds good. Might want to make sure the choke is closing all the way, this will hamper starts. Maybe try a different spark plug just to rule that out. Good luck.

 

[ryans4022]

No, havent tried any gas in the carb, will give that a try.....

 

[Adirondackstihl]

Remove the spark screen.
14mm or 15mm (cant remember which) deepwell socket to remove the exhaust tip.
Remove the screen any way you feel fit.

Is this the issue with your trimmer?....maybe....maybe not, but this process will eliminate that variable.

I've owned an FS45 for 4-5 yrs now. Great little trimmer. Serves me well.
I just had to replace the primer bulb this spring.

 

[ryans4022]

Oh yea forgot to metion that i did check the spark screen, it was clean as new!

 

[Adirondackstihl]

Check the "L" setting on the carb. I bet its a little lean. Try turning it out 1/4-1/2 turn and see if that helps.

 

[stihlaficionado]

I've found the choke setting to be finicky, ie., it easily floods.

The manual recommends starting w/o the choke if it continues to flood.
The first time I used it this season I couldn't get it started on choke. But after clearing out the
combustion chamber & drying off the plug I was able to start it w/o the choke, maybe 8-10 pulls.

 

[Adirondackstihl]

Prime 3-5x
Full choke....WOT
Pops on 3rd pull
Choke off....WOT....4th pull is running

Hasn't changed since I've had it from day #1

 

[w8ye]

Prime 3-5x
Full choke....WOT
Pops on 3rd pull
Choke off....WOT....4th pull is running

Hasn't changed since I've had it from day #1

I have both a 45 and a 55 and they both start as described above when cold.

Hot starting, I don't use the choke.

 

[BloodOnTheIce]

Looks like you've covered all your bases.

 

[ryans4022]

Alright wanted bring this up again, worked on it the other day again. Carb is clean, new plug, good fire, clean spark arrestor, good fuel lines and filter and new gas. Still will not fire........well maybe on the 63rd pull it will pop. The only way i can get it to pop is choke it and pull once or twice, choke off and after a bunch of pulls might pop once but not really trying to start at all. Forgot to mention the piston is clean on both sides, no scoring (can still see machine marks) and its carrying 120-130 psi compression. The seals dont show any signs of leaking either.

Im ready to just buy a new ebay shortblock.....my fs 55 did this exact thing and i ended up replacing the shortblock. I dismantled the old shortblock and all was in good shape so this ones a mystery to me and this is my second one with same symptoms.

 

[duramax99]

Try the splash of gas. the carbs on those trimmers are known to fail. Usually will run wfo and nowhere in between.

 

[sawfun9]

Well the Zama carb on my fs250 just failed a month ago. I don't know whether to rebuild it or get a new one. And my 250, while its been used hard, doesn't have a ton of hours on it and has always had non-ethanol fuel with Stihl ultra or XP oil.

 

[Scooterbum]

I had 2 FS55's do the same thing. Tried all the usual stuff and no fix. Beat my head on them for 2 weeks. I've had both since new. No engine should be that hard to start and that finicky.

Gave them to my boy and told him to part em' out. I now have 2 Echo SRM230's, SRM400 and a Shinny T27. Not looking back.

 

[Saw Dr.]

Coil failures are not uncommon on those. How does the intake gasket look? Also have seen s few cracked intakes from over tightening.

 

[BULLSPRIG]

+1 on the coil. Also make sure conn rod not bent.

 

[Rusty Barlow]

Is the plug getting wet? If not, squirt some premix through the carb. If it pops, I'd say fuel related. If not , electrical. Check the wire from the coil to the kill switch before jumping on a new coil.

 

[Wood Doctor]

I've found the choke setting to be finicky, ie., it easily floods.

The manual recommends starting w/o the choke if it continues to flood.
The first time I used it this season I couldn't get it started on choke. But after clearing out the
combustion chamber & drying off the plug I was able to start it w/o the choke, maybe 8-10 pulls.

Interesting... I flooded mine this morning after running a half-tank through it. It started OK cold. They flood easily when warm. I usually never choke a warm Stihl--chainsaw or line trimmer. Somehow I forgot my own rule. It only took two choke pulls to flood the warm engine. :bang:

I let it sit for 30 minutes or so and tried again with no choke. She started right up.

 

[ryans4022]

Plug is wet, getting too much fuel only because it wont start and fuel is collecting. But if I take it off choke, hold it wide open and crank it will pop then clean out but never start. Guess i will have to check the con rod, it has been hard to turn over sometimes from too much gas getting in there (maybe hydrolocked enuf to bend rod). I have swapped carbs with a good one so its not that. Intake gasket looks ok too. Guess i better check the coil too but it is firing ok with a tester and jumping the gap on the plug. Really got me thinkin bout the conn rod tho. Thanks ill have to tear it down.

 

[chainsawman2011]

Plug is wet, getting too much fuel only because it wont start and fuel is collecting. But if I take it off choke, hold it wide open and crank it will pop then clean out but never start. Guess i will have to check the con rod, it has been hard to turn over sometimes from too much gas getting in there (maybe hydrolocked enuf to bend rod). I have swapped carbs with a good one so its not that. Intake gasket looks ok too. Guess i better check the coil too but it is firing ok with a tester and jumping the gap on the plug. Really got me thinkin bout the conn rod tho. Thanks ill have to tear it down.

well no one has brought up a sheared flywheel key so I will I have had this happen
on many stihl chain saws never seen it happen on a trimmer yet but not impossible to
happen remove clutch and flywheel and make sure the the keyway is intact.