OLD FS-66 having issues

hwmonkey

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I have an older FS-66, like from the 1980s. I also have Stihl saws: 009 and 310. I like Stihl

My FS-66 is having issues. It didn't start. I took apart the carb and cleaned it. It had some build up. Got a carb kit that supposedly would fit and hunted down some gaskets that fit. The fuel pump portion seemed to not quite work. One of the flaps that should have opened seemed partially impeded. I resused the old, replaced the float, used carb cleaner, etc. I blew out the pickup hole (from the cylinder) which feeds the fuel pump. Spark looks good. Gap at 25. Air filter is clean. Exhaust looks clear (aired it out). Fuel line seems okay, for if I pressurize the tank (air through fuel line, it just spews the fuel out).

I struggled to get it to start. It was happiest when I pulled the plug, aired out the cylinder and plug, reassembled and immediately pulled the rope to start. I tweaked the L and H adjustments and I was able to get it started and running. It seems to run a little hot. H is at one turn out. L is about 1.25 turns. Starting fluid does not seem to help. It seems to have good compression, but not sure how high it is supposed to be.

I am using the same mix fuel as for my 009 which starts without a hitch. It is not new fuel, but not very old (this summer). It smells okay.

My issue is that it is difficult to start. When it starts, the choke is not on all the way. Most times, it does not want to start. Leave it alone for ahile and try later and your odds go up that it will start.

VERY short on cash, so taking it to the Stihl shop is not an option right now. Pulling my hair out. Any suggestions.

Any suggestions for what I could have missed or what might be needed?
 

bertsmobile1

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You really need to check the crankcase seals.
They do not last forever, even on Stihls.
Old saws that are difficult to start but will run ok , tending towards hot is a sign of air leaking past the crank seals.
Not a particularly difficult job, just a slow one.
Worthwile doing rings as well if the bore is clean.
 

hwmonkey

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Thanks. What should the compression be?

I pulled the fuel filter again, soaked it in carb cleaner, and re-installed having the same issues. I removed the fuel filter and... new problem. Now it seems to start fairly easily (without choke pull BTW in warm Florida). I tweak the low and high a little, as best I can. It seems to run okay for about 10 seconds at high rpm before it just dies. At lower rpm, it stays running. If I lift it into position to weed whack, it dies within about 5 seconds. The fuel line is staying at the bottom of the tank on the side that has fuel.

Obviously it needs a fuel filter. But why would it not stay running at higher rpms? I have the same issues with the H screw turned in too much or too far. The only things I can think of are:
  • Fuel line collapsing with more suction (too soft)
  • Fuel line leak
  • Float not right
  • Tank not venting right

Going to order fuel line/filter combo just in case. Not sure what the proper float setting would be. Nor do I know how to test the fuel tank ventillation (just the little hole in the cap on these, right?)

Thanks for ideas...
 

bertsmobile1

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A lot there to answer.
Firstly never ever run without a fuel filter fitted.
Running slow but not high suggests insufficient fuel supply.
There are some screens inside the carb that block up.
I use an alternative fuel supply that I know is good to check the fuel supply system.
The fuel line goes hard with time & cracks, some of the solvents in modern fuel also thend to make the fuel lines go to jelly and again block things up.
They oft crack inside the fuel tank so presurising the tank does not guarantee that the supply line is good.
On that carb, there are separate fuel supplys for the high & low speeds so if the high is blocked, the motor will run up to about 2/3 rpm but with no balls.
Compression is a difficult thing to specify on small blue smokes but generally anything under 70 psi is suspect & I like to see 90 + before I start to play with the carb.
 

hwmonkey

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A lot there to answer.
Firstly never ever run without a fuel filter fitted.
Running slow but not high suggests insufficient fuel supply.
There are some screens inside the carb that block up.
I use an alternative fuel supply that I know is good to check the fuel supply system.
The fuel line goes hard with time & cracks, some of the solvents in modern fuel also thend to make the fuel lines go to jelly and again block things up.
They oft crack inside the fuel tank so presurising the tank does not guarantee that the supply line is good.
On that carb, there are separate fuel supplys for the high & low speeds so if the high is blocked, the motor will run up to about 2/3 rpm but with no balls.
Compression is a difficult thing to specify on small blue smokes but generally anything under 70 psi is suspect & I like to see 90 + before I start to play with the carb.

I ran through everything and concluded that the earlier post about the seals leaking was right. Sometimes it would stall at idol, but when it warmed up and was unable to maintain high RPM seems like the obvious symptom. Not holding pressure. Fuel line was good, but replace anyway.

This carb has ONE fuel supply. This is an FS-66.

So, I can see the seals and the one on the magneto side looks like the culprit. BUT, the crankshaft has a woodruff key in it. On other motors I have worked on, this pin removes. But I cannot seem to get this pin out.

For example, look at the right side of the crankshaft in this image: http://www.forestryforum.com/gallery/albums/userpics/11009/SD_woodruff_key.jpg

How do I replace the seal on this side of the motor? I must get past this pin to remove the seal and to install the new one. Do I just need to hit it with a punch and hope I do not alter the shape of the woodruff key?

Thanks!!
 

hwmonkey

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Do I just need to hit it with a punch and hope I do not alter the shape of the woodruff key?
Disregard. I gave up, hit it with a punch and was able to remove it.
 

upupandaway

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I have an older FS-66, like from the 1980s. I also have Stihl saws: 009 and 310. I like Stihl

My FS-66 is having issues. It didn't start. I took apart the carb and cleaned it. It had some build up. Got a carb kit that supposedly would fit and hunted down some gaskets that fit. The fuel pump portion seemed to not quite work. One of the flaps that should have opened seemed partially impeded. I resused the old, replaced the float, used carb cleaner, etc. I blew out the pickup hole (from the cylinder) which feeds the fuel pump. Spark looks good. Gap at 25. Air filter is clean. Exhaust looks clear (aired it out). Fuel line seems okay, for if I pressurize the tank (air through fuel line, it just spews the fuel out).

I struggled to get it to start. It was happiest when I pulled the plug, aired out the cylinder and plug, reassembled and immediately pulled the rope to start. I tweaked the L and H adjustments and I was able to get it started and running. It seems to run a little hot. H is at one turn out. L is about 1.25 turns. Starting fluid does not seem to help. It seems to have good compression, but not sure how high it is supposed to be.

I am using the same mix fuel as for my 009 which starts without a hitch. It is not new fuel, but not very old (this summer). It smells okay.

My issue is that it is difficult to start. When it starts, the choke is not on all the way. Most times, it does not want to start. Leave it alone for ahile and try later and your odds go up that it will start.

VERY short on cash, so taking it to the Stihl shop is not an option right now. Pulling my hair out. Any suggestions.

Any suggestions for what I could have missed or what might be needed?

H is usually 1.5 + - turns not one. That would explain hard to start \ run hot \ loose steam after running for 2 seconds, etc.
 

bertsmobile1

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The H jet makes absolutely no difference to starting.
You can start it with the H closed right down or completely removed.
If you can't do that then the one way vlave in the carb is shot an so is the carb as it is not replaceale.
 

upupandaway

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The H jet makes absolutely no difference to starting.
You can start it with the H closed right down or completely removed.
If you can't do that then the one way vlave in the carb is shot an so is the carb as it is not replaceale.

"But why would it not stay running at higher rpms?"

I was replying to his H carb setting of 1 rev and the fact it will not stay running at high. He needs to fix that for a long term fix. Actually i might have posted the wrong # in that H may be 1.75 turns not the 1.5 i posted , i forget. not sure but round up when tuning the high mix.

bertsmobile1, with a shaft seal leak i have seen them as the cause of hard start if you dont pull fast enough. If huge, the leak is not allowing enough pressure in the lower chamber but if fast enough=enough pressure and it will run still leaking in the process.
Also, "one way valve" if u r talking about the gasket or needle, either IS replaceable. One can alter another carb to work - i did with mine.

Just saying...
 

Tim Murphy

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Sounds like your 66 is a lost cause....so will you please ship me your coil for my 66..I can't find one anywhere
 
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