stihl fs80 string trimmer lacks power

[rknarr2]

i have a stihl fs80 string trimmer that I bought used off ebay recently. The EPA sticker on the shaft has 1998 written in it so that is why I believe it was made around 1998 period. The carbeurator is a stihl S28D that has an adjustable screw for air intake into the carbeutor and thought that it might be the problem with it but then again I thought maybe its the low idle screw that needs adjusted I simply do not know and just guessing.
Here is what I have done to try to fix it as follows:
I tried to take the spark plug wire off the spark plug but it was stuck on to the spark plug but when I pulled on it the other end of the spark plug boot ripped the wire out of it. I took the stihl fs80 over to my brother in law and he put the wire back through the boot and I guess clipped it into that wire spring inside the boot. Well, he put the spark plug and attached it to the spark plug wire and put it up against metal on the side of the weedeater and pulled the starter pulley to make sure that it was creating a spark. That way he knew the coil was working and that the spark plug was working, too.
I put on a carbeurator kit, cleaned the orfices with starter fluid, cleaned the fuel tank, put on new fuel line with fuel filter and return lines. That did not seem to fix the problem I am having with it. When I start it up and let up on the trigger it wants to die off on me and also if I try to use it with the trigger fully pressed it gets sluggish when I cut weeds with it. Thank you for your assistance.
Regards, Robert

[lawnmon]

First, check for leaks around the carb. There is a black plastic spacer flange, part # 4137-121-1601 or 4137-121-1600, that holds the carb away from the cylinder. Check it for cracks. If the trimmer gets worse as it heats up, this could be the problem.

But, I'll bet you put a new carb on it, it'll run like new.

Good luck

[rknarr2]

That might work putting on a new carb but I wanted to exhaust other less expensive means to avoid it. I will check that black plastic spacer flange for cracks and check for leaks around the carb, too. Thank you for the suggestions.

[rknarr2]

I received the following suggestions from an ebay seller who is selling small engine manuals as follows:
check your plug and valve? as long as its clean and properly gapped. single fire doesn't always mean repetitious fire. what about the valve...make sure its not sticking any. did you take and make sure float was internally dry? and needle valve and seat were clean and properly placed?

[milike]

a few $ for a new zima carb and you'd be all set

[lawnmon]

One other item to check is the exhaust/muffler for restrictions. Many are very clogged and they won' run well like that.

[rknarr2]

I put a brand new muffler on the weedeater so the screen is not clogged up. I was told to remove that screen on the old muffler on the phone from a stihl service person but it was all ready taken out. Thank you.
Regards,
rknarr2

[rknarr2]

I took the spacer flange part, 4137-121-1600, off and cleaned it up with soap and water. I then checked it for cracks and I found a stress crack along the entire side wall which was probably from a person who over tightened the bolt(s) that caused the stress crack to occur or when I took the bolt(s) out I caused the stress crack by pushing down on the bolt as I loosened it. In any case, I will have to replace it. Thank you lawnmom I will let you know after I get a new one if it fixes the lack of power problem. Regards, Robert

[topsites]

I had a similar problem and I got so tired of it doing that, I accidentally figured something out.

Now I can't recommend you do it, but just like yourself I replaced the carburetor and hence had a spare...
That wasn't the only thing I had replaced but long story short I was a bit pissed, so one day I took a
needle nose vise grip and clamped it on to the HIGH adjustment screw, the plastic part.

Then I turned it up to where the plastic hits that stop and kept going until that POS
plastic sleeve broke and allowed the adjustment screw to go past the stop.

Once that was done it was easy to adjust it, and I got it running pretty good
with the high end screw somewhere past the manufactured stopping point.
Doesn't run 100% perfect but it's close enough for me.

As I said I can't tell you to do that, but when I asked about this at the dealership they said the procedure isn't unheard of.
I also heard other folks saying you just have to learn how to 'adjust' it...

Mine's an FS-80r, 2001 model.
Good luck.

[rknarr2]

I put on a new flange spacer but that did not help.
As I mentioned above, I have also put on a new muffler and put on a carburetor kit but those did not help either.
So, maybe if I take the valve seal out of the carburetor and clean that in mineral spirits and replace the spark plug might be the next things I will try.
If that would not fix it, then should I look at taking off the cylinder and looking at the valves to see if they are sticking or taking a look at the idle speed on the carburetor. I am not sure what to try next running out of options and ideas. If you want to know what my problem is please review the initial thread above. Thank you.
Regards,
Robert

[lawnmon]

I put on a new flange spacer but that did not help.
As I mentioned above, I have also put on a new muffler and put on a carburetor kit but those did not help either.
So, maybe if I take the valve seal out of the carburetor and clean that in mineral spirits and replace the spark plug might be the next things I will try.
If that would not fix it, then should I look at taking off the cylinder and looking at the valves to see if they are sticking or taking a look at the idle speed on the carburetor. I am not sure what to try next running out of options and ideas. If you want to know what my problem is please review the initial thread above. Thank you.
Regards,
Robert

Robert,

There are NO valves in this engine, it's a 2 stroke.

I know you don't want to hear this, but that carb needs replacing.

joat

[rknarr2]

I finally just took the weed eater to the stihl shop. I told him everything that I did and he was first surprised that what I did did not fix it then he asked me who did the work on it? I told him I did and that he thought it was still a gasoline problem. He asked me if I took any of the welch plugs off and pulled something out and cleaned it. I am thinking he is referring to the valve jet out of its seat. According to a stihl service manual that I bought recently, it says to use a 5 mm (approx. 3/16") dia. drift to press the valve jet out of its seat in the direction of the venturi (not sure what a venturi is) and wash it in white spirit. It might also be possible that i put in one of the gasket in wrong like the diaphram.
Robert

[rknarr2]

The stihl shop repair man told me that there were no valves as you stated in your reply and that the guy that suggested me to check float to make sure it was dry in the carburator. Well, the stihl shop man told me that my carburator does not have a float in the carburator it uses instead a diaphram. So, when I put in carburator kit it was part of it. I just hope that he can fix it without me having to pay for a new carburator but if he puts on a new carburator so be it. Thank you for all your support with my problem and in a week I should have my weedeater back and hopefully running correctly. Regards, Robert

[milike]

I finally just took the weed eater to the stihl shop. I told him everything that I did and he was first surprised that what I did did not fix it then he asked me who did the work on it? I told him I did and that he thought it was still a gasoline problem. He asked me if I took any of the welch plugs off and pulled something out and cleaned it. I am thinking he is referring to the valve jet out of its seat. According to a stihl service manual that I bought recently, it says to use a 5 mm (approx. 3/16") dia. drift to press the valve jet out of its seat in the direction of the venturi (not sure what a venturi is) and wash it in white spirit. It might also be possible that i put in one of the gasket in wrong like the diaphram.
Robert

All the 'cost' of going through this thorough cleaning to 'save' an old carb...it would be cheaper and quicker to just spring for a new carb.

[twotone]

Do a compression check. A cracked piston ring could be the problem.

[hate2work]

Welch plugs are small, aluminum domed discs that are pressed into place over the low speed acceleration ports for access to these ports at a later date by the mechanic.

It's pretty rare to see an intake manifold cracked, but it does happen. Most often the replacement makes the machine run well again, as it no longer has an outside source of air.

It sounds like you have what Stihl calls a BIS carb, or Balanced Idle System. We call them a BS carb, that should give you a clue about them.

Once we determine the spark and compression are good, I will attemp to clean a carb one time. If it still will not pull fuel, a new carb is put on. A new carb is almost always a better fix. No comebacks and a better performing piece of equipment.

Needle limiter caps are a pita and we are always removing them so an adjustment can be made. They are a product of the clean air laws, as they will not let you richen the carb too much.

Robert, no offense, but if you don't even know what a venturi is, you really shouldn't be working on your carb. The 4137 series engine was a good one, we were still selling the FS-80 up until just last week when it became NLA.

[rknarr2]

Got the weedeater back from Stihl shop. It was NOT the carbeuator like alot of you people thought. He showed me that an upper edge of the crank case had broken off and that its been like that for along time because of the roundness in the edge. He also showed me where the edge of
the piston had a worn place on it.
He told me it would cost me the following to fix it:
Part Part Number Price
Crank case 4137-020-2800 $67.60
Piston 4137-030-2010 $63.55
2 rings 4137-034-3000 2*$8.65 = $17.30
piston pin 4137-034-1500 $ 8.95
bearing 9512-003-1830 $ 9.00
cylinder gasket 4137-029-2300 $ 2.00
his labor (approximately 2 hours) $80.00
Grand total $248.40
+ tax

[hate2work]

Robert, this reminds me of trying to diagnose a problem over the phone. We're always getting people calling us, asking what the problem is < chuckle >

Anyway, if you're going to have it repaired, have the dealer order the short block for this machine rather than all the individual parts. That's a much better way to go.

If you have the BIS carb the part # for the short block is 4137-020-0201.

If you have the adjustable carb, the part # is 4137-020-0202.

The MSRP for each is $97.95. The labor should also be a little less if you went this way.

Hope this helps :)

[rknarr2]

That is a great idea to do a short block and it would cut the labor costs as well. I checked with my local stihl and was told that the short block $175 but I would also have
to change out my old carb, S28D, which is around $60-$70 because it would not work with a short block.
If I purchased individually, the stihl guy told me that I would need to add the following:
Oil seal 9640 003 1195 $6.45
Tube of sealant Dirko HT red(B) $14.99
to this list previous mentioned in my last post:
Part Part Number Price
Crank case 4137-020-2800 $67.60
Piston 4137-030-2010 $63.55
2 rings 4137-034-3000 2*$8.65 = $17.30
piston pin 4137-034-1500 $ 8.95
bearing 9512-003-1830 $ 9.00
cylinder gasket 4137-029-2300 $ 2.00
his labor (approximately 2 hours) $80.00
Grand total $248.40
+ tax
However, I would not have to buy the following as stated by that other stihl shop:
2 rings 4137-034-3000 2*$8.65 = $17.30
piston pin 4137-034-1500 $ 8.95
because these items are included with Piston 4137-030-2010 $63.55. Either that other
stihl shop made an honest mistake or was going to try to charge me twice for the 2 rings and piston pin.

This stihl shop gave me a total $182.74 parts + 2 hours labor ($48/hour)= $278.74+tax
Thank you for the response.

[rknarr2]

I made a mistake when I said in my previous post that I would also have to change out my old carb, S28D, which is around $60-$70 because it would not work with a short block.
I would not have to buy a carb because I was given the part number for both blocks with BIS and Adjustable carb in the last previous response from hate2work. Sorry about that.

[hate2work]

Robert, you shouldn't have to change your carb, as both styles of shortblocks are still available. See my post above for the part numbers.

Good luck :)

[rknarr2]

I realize that I made a mistake on the carb because you had given me both blocks for the different carbs and I wrote a post above on it. If I could have edited when I realized it, I would have edited the post that I made the mistake in instead of a new post.
Thanks
Rob

[topsites]

All right, here's what you do:

1. Take that POS and hurl it in the general direction of the trash, try and get some good air with it or throw it in such a
way that you might get at least some satisfaction... But if that doesn't work, a big hammer can do wonders as well.
2. Go back to the Stihl Dealer and get yourself a brand new trimmer, a nice one run you 250-300.
3. Chalk one up to experience.
4. Over and out, done.

[rknarr2]

I have to replace the piston on my stihl fs80r weed trimmer. The top of the piston has carbon powdery deposit on it while the side of the piston has scratch marks and there is a burnt place on the side and top.
1. Would the burnt place on the side and top be from the spark plug during sparking process and is that normal to see that?
2. Before I change out the piston, what is used to clean the carbon deposit out of the inside bore of the existing used cylinder? I am not sure what to use gasoline, mineral spirits, propyl alchohol, starter fluid, carburator cleaner etc...

Thank you for the assistance.

Robert

[rknarr2]

Anyone have idea where I find some good cheap priced but in good used or new good Stihl parts for a Stihl fs 80 string trimmer as follow?
Part No. Part Description
4137 020 2800 Crankcase, starter side
4137 030 2010 Piston
4137 180 1150 Throttle cable

Thank ya much.
Robert

[STIHL GUY]

One other item to check is the exhaust/muffler for restrictions. Many are very clogged and they won' run well like that.

i just cleaned the exhust screen in my trimmer and what a diffrence. i heated it up with a torch and cleaned it off with a wire brush and its good as new

[rknarr2]

I appreciate the advice about the muffler restriction but I had Stihl repairman who showed me top cracked off edge on the crank case, starter side and the scratches on the piston. Plus, I put on a brand new muffler before I took the trimmer to the Stihl repairman. Thank you.
Robert