Help with a Stihl FS80 AV with a TK carburetor

[John Lyngdal]

Came across this old FS80AV string trimmer in really nice shape at a garage sale for $50. It has 165 psi of compression and looks like it has seen little use. It sorta ran when I got it, but the spark plug looked as if was running lean. Filled up the tank with fresh 40:1 non-ethanol premium, added a cap full of Sea Foam, and let it run at about 6000 rpm with the choke half on. Just wanted to see it that would help. I let it run through the tank while sitting on the bench, then checked the plug. It looked about right. Loaded up another tank of fuel and started right up, but still wouldn't run above 7500 rpm, so I let it burn through the second tank of fuel on the bench. At the end of the second tank there was still no improvement, so I replaced the fuel line and bypassed the priming bulb, and now it barely runs. <sigh> It seems all the all the posts about the demonically possessed TK carburetors is true. I then pulled the cover and took a look at the carburetor diaphragm and it wasn't very flexible. Put it back in, and now I can't even get it started. Not sure if I should just use the common parts as spares for my FS86, install a carb kit in the TK, or purchase a more modern style carburetor and air filter housing.

Suggestions from those that have traveled down this path would be most welcome.

 

[backhoelover]

@ray benson can you send him the service manual please sir

 

[backhoelover]

unit will need a carb kit

 

[ray benson]

@ray benson can you send him the service manual please sir

Sent ipl and a link for the 12 meg service manual.

 

[DND 9000]

@ray benson: Is there a service manual for the old FS 80 AV (4112) existing?

 

[backhoelover]

Yes it's on flash drive heading your way wife was with mil last night she will be home today for me to send you tracking info

 

[ray benson]

@ray benson: Is there a service manual for the old FS 80 AV (4112) existing?

Check your inbox

 

[John Lyngdal]

Thank you for the service manual!
Time to see if that will help me address the issues.

 

[DND 9000]

Thanks a lot Ray (see also your PM).

 

[John Lyngdal]

Things are looking up. Reset the jet settings and had the trimmer running at ~10,000 rpm and would drop down to idle and back up to speed. At idle or at speed I get no change in the rpm when adjusting the low speed adjustment, so I'm guessing it's clogged and I'm just running off the high speed jet. The other issue is that the engine acts like the fuel tank vent is clogged(but isn't). It starts acting like the engine is undergoing fuel starvation, but returns to normal when the cap is removed. The primer bulb is still removed from the system currently. My first thought is that the stiffened carburetor diaphragm is the likely cause, am I missing another possibility? I've started shopping for a rebuild kit for the carburetor, do the TK1 and TK4 carburetors use the same kit or which model in on the FS80? So far I've found these kits available:

http://tewarehouse.com/7-07167
https://www.jackssmallengines.com/jacks-parts-lookup/part/jacks/jse2672272
Anywhere else I should look?

John

 

[LegDeLimber]

Is that carburetor close to this?
https://www.ebay.com/sch/i.html?_pr...c&_sop=15&isRefine=true&LH_ItemCondition=1000

 

[John Lyngdal]

It is, but I'll need to pull off the current carburetor to be sure.
I actually like the replacement option better as I have something that works OK for backup as compared to nothing if after the rebuild it runs worse.

 

[ironman_gq]

You can try to clear the low speed passage, what I've done in a pinch (or if I don't feel like pulling the carb apart) is pull the low speed needle, take a can of non-chlorinated brake cleaner (the flammable stuff) and stick the straw right in the needle hole and blast it out. Give it a couple short blasts and let it sit for 10 minutes then repeat. I try to point the carb down so the brake cleaner doesn't run into the engine. Usually have a 70% success rate on varnished carbs doing this.

 

[John Lyngdal]

And closure to the saga....
Tried to use a Shindiawa B45 TK carburetor and while close mechanically, the choke control as positioned so that it wouldn't work on a FS80.
The original FS80 carburetor diaphragm was an ethanol induced mess, so I ordered a rebuild kit from a US based supplier www.ebay.com/itm/322364531230
for $9.00 and had in in three days. Installed the new diaphragm, adjusted the High and Low settings using the Shindiawa T25 manual and the unit now functions perfectly.

 

[alderman]

Good ending to the saga.


Sent from my iPhone using Tapatalk

 

[jjnga]

Came across this old FS80AV string trimmer in really nice shape at a garage sale for $50. It has 165 psi of compression and looks like it has seen little use. It sorta ran when I got it, but the spark plug looked as if was running lean. Filled up the tank with fresh 40:1 non-ethanol premium, added a cap full of Sea Foam, and let it run at about 6000 rpm with the choke half on. Just wanted to enough see it that would help. I let it run through the tank while sitting on the bench, then checked the plug. It looked about right. Loaded up another tank of fuel and started right up, but still wouldn't run above 7500 rpm, so I let it burn through the second tank of fuel on the bench. At the end of the second tank there was still no improvement, so I replaced the fuel line and bypassed the priming bulb, and now it barely runs. <sigh> It seems all the all the posts about the demonically possessed TK carburetors is true. I then pulled the cover and took a look at the carburetor diaphragm and it wasn't very flexible. Put it back in, and now I can't even get it started. Not sure if I should just use the common parts as spares for my FS86, install a carb kit in the TK, or purchase a more modern style carburetor and air filter housing.

Suggestions from those that have traveled down this path would be most welcome.

Been down that road. Looked for carb parts for months. Bought all kinds of old parts for the original carb and found a Chinese carb that fit and kind of was the same type (tk) Found a nos carb and a rebuild kit. Not a fun carb
to work on. New fuel line primer bulb inlet line with filter. Now starts right up then seems to run out of gas. Good luck. Let me know if you have better luck. I bought this new in the 80's and sat around for years after it stopped running when you raised the head above the engine. Did not know anything about 2stroke engines then. Have learned enough to be dangerous now.