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FS-80 Stihl Trimmer, Erratic Performance

Discussion in 'Mechanic and Repair' started by Jay Ray, Dec 16, 2006.

  1. Jay Ray

    Jay Ray LawnSite Fanatic
    Messages: 6,510

    I searched old threads and think I tried every suggestion. This is my spare FS80 and it is 3 years old. My main FS80 still runs good.

    The ignition coil is probably the problem in my opinion, but here is what has been done so far:

    New carb, fuel hoses, fuel filter, and tank grommets last March.

    New fuel cap, air filter, and two new plugs today (in case the first might have been bad out of the box).

    Took muffler off. Port is clear. Bore looks near perfect. Machining marks still visible and even (no evidence of slap) on all of the piston skirt that can be seen. Top of piston looks good. Rings look good.

    The cord is still as hard to pull as my main FS-80, so am assuming it has good compression.

    It is getting fuel because you can see the mist shoot out (muffler off) in the sunlight when pulling the cord. But it will not start today. Used it a few days ago just to run some fuel through it and it had plenty of power. But it has been getting harder to start as the season wore on.

    My question is this: When I take the coil in to the dealer do they have an instrument or machine to check it with, or will it be just my word that it is probably bad?
  2. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,283

    Take a voltmeter that measures resistance and measure from the inside of the wire that goes to the plug to ground on the trimmer. Compare the resistance between your two units. Yes the shop can do the same or check for a spark. Have you tried checking for spark by unscrewing the plug and hook the wire on it and touch the plug to the top of the engine while pulling the cord. Should be able to see the spark. Also could disconnect the kill switch just to be sure that isn't a problem but doesn't sound like it is.
  3. Jay Ray

    Jay Ray LawnSite Fanatic
    Messages: 6,510

    Thanks. It's a little over 500,000 ohms on both trimmers using a multi-meter. Kill switch is not affecting it.

    I'm going to borrow some insulated gloves and try wrestling with it again to check the spark.

    Don't know if they still use them, but I remember having coils tested for cars on what they called a high freq tester. Hope the dealer has something like that.
  4. Jay Ray

    Jay Ray LawnSite Fanatic
    Messages: 6,510

    Had spark with plug grounded to the jug.

    I hung it on hooks overhead in the shop last night and the air cleaner ended up low, and fuel was dripping out of the air cleaner onto the floor this morning. I was assuming because the carb is 9 mos. old it was okay, but will have to look into it. Maybe it is getting too much fuel and flooding. That squares with getting harder to start as the season wore on too.

    Anyway, am setting it aside so as not to get too frustrated with it.

    I took a hedge trimmer under warranty to the dealer last year. He cleaned the carb and put in a repair kit. No luck. He slapped a new carb on it and it is still running great. He was very frustrated with not being able to repair the original carb and thought it had a manufacturing defect. I would have hated to see the bill on it if it wasn't under warranty. I guess what we hear about 2-cycle stuff being cantankerous and contrary is true.
  5. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,283

    Have you tried getting all the gas out of the system to ensure no water? A nine month old carb should not be a problem unless it has got dirt into it. Try getting some quick start and spray it into the carb with choke open. I see gas pour out of the Echo units all the time and that don't seem to affect them. Try swapping the carb between your two units, that is the great advantage of sticking with one brand of trimmers and the same model.
  6. LCPullman

    LCPullman LawnSite Senior Member
    Messages: 589

    I had trouble once where my Echo blower was very hard to start, turned out one of the crankshaft seals had popped out and thus not enough fuel was getting to the cylinder.

    Based on my experience, if there is fuel leaking out the air filter on Echo equipment, the tank pressure relief valve needs replacing (cheap white plastic part). I'm not sure if any other manufacturers have that though.
  7. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,283

    Yes those seals on crankshaft can cause problem on Echo but I never had one to come out on Stihl. By the way the white plastic device is not a pressure release valve but a breather. When it is broke fuel can escape out of it and that is bad. No pressure relief on an Echo that I am aware of so it does come thru the carb on hot days if the needle valve allows it, but I could be wrong?
  8. Jay Ray

    Jay Ray LawnSite Fanatic
    Messages: 6,510

    Was looking at a generic diagram (Figure 9-42) in Repairing Your Outdoor Power Equipment by Jay Webster. Looks like if the needle valve goes bad the high speed circuit has a ball check on it, but looks like the idle circuit would pour gas right into the main bore (throat) of the carb by gravity feed if the trimmer was rotated into certain positions with the tank being high.

    Paid around $60 for a new carb last time. Probably worth it again to keep a $300 unit working. Just looking at Webster's diagram it looks like replacing the needle valve would have limited access and be difficult with a repair kit.

    Was shocked to get a couple calls for cleanups and haven't been able to get back to it.
  9. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,283

    Kinda strange to have two carb that are broke. I would try to get a kit and learn how to replace the needle valve since it is very easy. Usually on echo there are a number of rubber/plastic gasket that are much more important and a screen to clean. And the jet needs to be cleaned. Did you switch them yet?
  10. Jay Ray

    Jay Ray LawnSite Fanatic
    Messages: 6,510

    Not yet. Have put kits in 4-cycle carbs and in diaphragm fuel pumps for honda and kawi, but never a 2-cycle carb. Somebody told me to just buy a new carb, not to mess with them. We are in for some rain Thursday so will tinker then.

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