fs36 stimmer won't start?

[sandspider]

Right, eventually got the correct carb kit (walbro wt-160B carb, not Zama) and replaced the various diaphragms. Metering diaphragm was shot, dissolving and floppy.

Strimmer now runs!

 

However, it's not set up quite right. It would cough but not start on choke, but I managed to start it without choke by opening the throttle a bit. Once it warmed up it would idle fairly well without throttle, but kept stalling. It also wouldn't rev fully, maybe 75% (a guess by sound, I don't have a tach) Once stalled it would restart with a bit of throttle.

 

So I'm guessing the high and low screws needs adjusting. Tried to find default settings on the internet (2 turns out each?) buy found conflicting info. Does anyone know the correct default settings and a reliable tuning procedure? I assuming running it a bit rich isn't the end of the world, but running it too.lean could be...

 

Many thanks.

[sandspider]

Right, eventually got the correct carb kit (walbro wt-160B carb, not Zama) and replaced the various diaphragms. Metering diaphragm was shot, dissolving and floppy.

Strimmer now runs!

 

However, it's not set up quite right. It would cough but not start on choke, but I managed to start it without choke by opening the throttle a bit. Once it warmed up it would idle fairly well without throttle, but kept stalling. It also wouldn't rev fully, maybe 75% (a guess by sound, I don't have a tach) Once stalled it would restart with a bit of throttle.

 

So I'm guessing the high and low screws needs adjusting. Tried to find default settings on the internet (2 turns out each?) buy found conflicting info. Does anyone know the correct default settings and a reliable tuning procedure? I assuming running it a bit rich isn't the end of the world, but running it too.lean could be...

 

Many thanks.

[BishBashBosh]

... Tried to find default settings on the internet (2 turns out each?) buy found conflicting info. Does anyone know the correct default settings and a reliable tuning procedure? I assuming running it a bit rich isn't the end of the world, but running it too.lean could be...

 

From fully seated, open each

H 1.5

L 4.0 (yes four, not a typo)

 

Those are the starting positions from the Stihl Carb Manual, here's a link to the pdf.

http://thebakeliteradio.com/sawspares.com/stihl%20carburetor%20manual.pdf

 

I've only ever tuned with a tacho, if you get it running then perhaps get your local service guy to give it a test'n'tweak for a few quid?

[sandspider]

Ahh, thanks BBB. That looks a good place to start.

[GardenKit]

Tuning procedure, without tach.

 

As its ticking over after a fashion you are part way there already. Firstly tune the WOT with the H screw. Before attempting to tune, make sure the 2 line head is fully wound and the 2 lines are both extended to the correct length, as the length of line controls the max speed.

 

Rev the machine flat out for a minute or so, then adjust the H screw. Try it clockwise first. If the revs increase keep turning it clockwise until the revs peak then start to drop off (lean drop off point). Then turn slowly counter clockwise, the revs will peak then hold steady for a small amount of turn before dropping off at the "rich drop off point". Turn slightly clockwise from this point until trust before the revs start to peak. Leave it there for now. Don't start listening for "four stroking", this is a strimmer so is working under load even when not in work.

 

Now turn your attention to the L screw. Let the machine idle if it will and turn the L screw in the same manner as we did the H. First turn clockwise until the idle peaks and then drops. Then turn counter clockwise until the revs start to drop off and the engine gets a little lumpy. Then turn slightly clockwise until the idle smooths out. So we are close to the rich drop off point rather than the lean drop off point.

 

Set the Idle speed screw to give a smooth tickover a little below the point at which the centrifugal clutch engages. Repeat the L screw adjustment.

 

Let it idle for half a minute then blip the throttle. If the engine picks up smoothly then everything is good, but if the engine falters or refuses to rev from tick over, then turn the L screw slightly to rich (counter clockwise) and try again.

 

Sometimes a compromise needs to be made between the smoothest tick over and the best pick up.

 

These adjustments all assume that the carb is in perfect order and correctly set up. In particular the height of the needle valve arm, as if too high the mix will be rich and if too low it will be lean.

 

Also, ensure that you turn the screws very, very slowly and keep an awareness of the the screwdriver position at all times.

 

Hope this is understandable and that it it helps.

[sandspider]

Many thanks for typing all that out Gk, it does make sense and it certainly does help!

 

Cheers.

[sandspider]

Sorry guys, I still can't get the bugger working! Any.more suggestions please?

 

I reset the carb to default settings (that may have been a mistake!), but after some tweaking I can only get it to run very briefly (a second or two) on WOT. Same whether choke is on or off.

 

Spark plug is new, air filter is clean, fuel lines are solid, carb is rebuilt and cleaned.

 

Fuel appears in the primer bulb, and stays there. A little.bubble.of air at the top of the bulb. If I push the bulb again it may run for another stroke.or two.but not much difference. Fuel is fresh.

 

Any more thoughts before I chuck it and buy a florabest?! I can't remember exactly where the carb screws are in the end, but it doesn't seem to make much difference anyway.

 

I tried a couple of local service places, and the only.one to get back to.me.is a six week wait and 35 quid.minimum.just to look at it!

[EricBradley]

Sounds like the carb is not clean enough, have you had it in a ultrasonic cleaner? if not and you don't know anyone with one most motorbike shops have one and will charge around £15 to boil it for half an hour.

[sandspider]

No, just dismantled it and lots of carb cleaner. However, it did run for a bit after cleaning, to the extent I could do a bit of strimming with it.