THALL, Stihl techs, anybody - FS80 trimmer won't start

KMB · Nov 19, 2009

I’m trying to get a friends Stihl FS80 trimmer running. It isn’t getting mix to the cylinder. I can pour some mix into the cylinder and it will fire and run for a few seconds, so there is spark. I went through the carb and even tried it on a Stihl FS76 trimmer that I have access to, and it worked on that trimmer. So the carb should be okay.

The fuel pickup body is new. My friend got the new fuel line from his dealer (I think a Stihl dealer). The old hose needed replacing. The new hose is a piece of rubber hose with the correct ID to attach to the carb and fuel pickup body. The new hose is also ‘softer’ than the OEM hose. I don’t know if the old OEM hose was ‘harder’ from age or if they are fairly hard/stiff even when new. I also made sure that there were no kinks in the hose. With the hose in place (through the tank grommet), I was able to get good air flow through the hose.

Is there special hose that is needed? In the IPL there is no hose part number, just the hose dimensions (3.1 x 5.7 x 180mm for the fuel hose). What have I missed? What else could be the problem?

Kevin

lawnmowertech37 · Nov 19, 2009

KMB said:
I’m trying to get a friends Stihl FS80 trimmer running. It isn’t getting mix to the cylinder. I can pour some mix into the cylinder and it will fire and run for a few seconds, so there is spark. I went through the carb and even tried it on a Stihl FS76 trimmer that I have access to, and it worked on that trimmer. So the carb should be okay.

The fuel pickup body is new. My friend got the new fuel line from his dealer (I think a Stihl dealer). The old hose needed replacing. The new hose is a piece of rubber hose with the correct ID to attach to the carb and fuel pickup body. The new hose is also ‘softer’ than the OEM hose. I don’t know if the old OEM hose was ‘harder’ from age or if they are fairly hard/stiff even when new. I also made sure that there were no kinks in the hose. With the hose in place (through the tank grommet), I was able to get good air flow through the hose.

Is there special hose that is needed? In the IPL there is no hose part number, just the hose dimensions (3.1 x 5.7 x 180mm for the fuel hose). What have I missed? What else could be the problem?

Kevin

kmb have you checked the muffler on the muffler if im not mistaken there is a cady on that muffler on the side where you can remove the cady from the muffler with a wrench if that cady is plugged it wont start period

check to see if your muffler is one of them type mufflers
if im not mistaken that muffler acts as a breather on them units as well and if it has a clog it wont allow it to run period
also poor compression can cause a issue as well

BloodOnTheIce · Nov 19, 2009

lawnmowertech37 said:
kmb have you checked the muffler on the muffler if im not mistaken there is a cady on that muffler on the side where you can remove the cady from the muffler with a wrench if that cady is plugged it wont start period

check to see if your muffler is one of them type mufflers
if im not mistaken that muffler acts as a breather on them units as well and if it has a clog it wont allow it to run period
also poor compression can cause a issue as well

As well check the exhaust port, carbon can build up there or the muffler and cause your problems.

lawnmowertech37 · Nov 19, 2009

BloodOnTheIce said:
As well check the exhaust port, carbon can build up there or the muffler and cause your problems.

and im not even a stihl tech well use to be for a local hardware store my brother uses a fs80 in his landscape business

KMB · Nov 19, 2009

Thanks fellas. I'll check those things and do a compression test tomorrow.

Kevin

KMB · Nov 25, 2009

An update. The compression is at 130 psi. The exhaust port is clean. The muffler is rusty, but looks fine (I blew air through it). I didn't see where there was a 'cady' on the muffler. Still no fuel to the cylinder.

I don't know the proper terminology, but it seems like the fuel is not being able to be drawn up out of the tank, through the fuel line and into the carb. Is there way to confirm/test this? I assume the tank is vented through the tank cap, could that be the problem?

Kevin

Soby1 · Nov 25, 2009

Never worked on that trimmer but it sounds like the impulse line or (port) not sure what that has could be broken or blocked by the intake gasket.

KMB · Nov 25, 2009

Soby1 said:
Never worked on that trimmer but it sounds like the impulse line or (port) not sure what that has could be broken or blocked by the intake gasket.

There is no impulse line. There is a spacer flange between the (carb and cylinder) that I cleaned and checked out. I'm not sure how 'impulse' works on this trimmer, but I'll have a look to see if I can figure it out and make sure the passages to the carb are clear. I'm sure they are...but it won't hurt to look again.

Kevin

Scooterbum · Nov 25, 2009

Impulse travels through a small hole in the intake.Make sure it's not blocked in the flange or gasket.Also check the cylinder.

KMB · Nov 25, 2009

Scooterbum said:
Impulse travels through a small hole in the intake.Make sure it's not blocked in the flange or gasket.Also check the cylinder.

Thanks for that, will do. P&C are in great condition, as I saw through the intake and exhaust ports.

Kevin

Nitro-Fish · Nov 25, 2009

If you removed the carb spacer when you removed the carb, make sure the holes in the spacer, the cylinder & the carb are all lined up. What year trimmer (if you know) the older ones that have the TK slide valve type carb can be a real PITA!

KMB · Nov 25, 2009

Nitro-Fish said:
If you removed the carb spacer when you removed the carb, make sure the holes in the spacer, the cylinder & the carb are all lined up. What year trimmer (if you know) the older ones that have the TK slide valve type carb can be a real PITA!

Will do. Shouldn't the 2 mounting screws align everything up?

The trimmer is the newer version...according to the 2 different IPL's I have.

Kevin

Soby1 · Nov 25, 2009

KMB said:
Will do. Shouldn't the 2 mounting screws align everything up?

The trimmer is the newer version...according to the 2 different IPL's I have.

Kevin

Yes but what I've ran into is people putting the gasket on upside down and blocking the impluse port with the gasket.Done it a few times myself.

KMB · Nov 25, 2009

Soby1 said:
Yes but what I've ran into is people putting the gasket on upside down and blocking the impluse port with the gasket.Done it a few times myself.

Understood, gotcha. Man I hope that is the problem.

Kevin

Termite · Nov 25, 2009

I worked on a friends Stihl trimmer that would not start. It would pop sometimes but not run. It had me puzzled so I ask for ideas on here. They nailed the problem. Ignition module even though it had spark the timing went way off on failure.
May not be your problem?
He got a new module under warranty.

Fish · Nov 25, 2009

If you have swapped the carb onto another trimmer, and it runs ok, and can pour some gas in and it will run a few seconds.
And you have checked the block and gaskets under the carb and they are
fine, then it sounds like you have a totally blown seal, and the air is sucking in there, and not through the carb.
So a leakdown test would be my next suggestion. I have seen the seal under the pull starter blow out totally.

KMB · Nov 25, 2009

Fish said:
If you have swapped the carb onto another trimmer, and it runs ok, and can pour some gas in and it will run a few seconds.
And you have checked the block and gaskets under the carb and they are
fine, then it sounds like you have a totally blown seal, and the air is sucking in there, and not through the carb.
So a leakdown test would be my next suggestion. I have seen the seal under the pull starter blow out totally.

Hadn't even crossed my mind. Thanks for that. I'm going to confirm that the spacer holes and gasket holes line up. If still know go, then I'll do a pressure and vacuum test as you suggest. When you say leakdown test, is that the same as pressure and vacuum testing?

Kevin

THALL10326 · Nov 25, 2009

KMB said:
Hadn't even crossed my mind. Thanks for that. I'm going to confirm that the spacer holes and gasket holes line up. If still know go, then I'll do a pressure and vacuum test as you suggest. When you say leakdown test, is that the same as pressure and vacuum testing?

Kevin

Sorry KMB just now noticed this thread. Fish gave you the right answer. If you got a huge crankcase leak, seal blown, the engine can't draw much if any fuel through the carb. You need to either do a vac/pressure test or leakdown test to make sure of the basics are covered first before. Once you get your tests done you'll be able to nail down the problem much easier..

KMB · Nov 25, 2009

THALL10326 said:
Sorry KMB just now noticed this thread. Fish gave you the right answer. If you got a huge crankcase leak, seal blown, the engine can't draw much if any fuel through the carb. You need to either do a vac/pressure test or leakdown test to make sure of the basics are covered first before. Once you get your tests done you'll be able to nail down the problem much easier..

And thank you. I'm just in the process of making an adapter for the spark plug holes on my OPE for pressure/vacuum testing. I'll give an update in a day or 2.

Kevin

KMB · Nov 25, 2009

KMB said:
When you say leakdown test, is that the same as pressure and vacuum testing?

I googled my question and now know the difference and how leak down testing is done.

Kevin

THALL, Stihl techs, anybody - FS80 trimmer won't start

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