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Problems with trimmer and blower (again)

Discussion in 'Mechanic and Repair' started by Envy Lawn Service, Jul 23, 2005.

  1. Envy Lawn Service

    Envy Lawn Service LawnSite Fanatic
    Posts: 11,062

    Well, here I am again, a year later and I'm back to the same problems.
    Here is last year's thread if it helps.


    Both have been up to their old tricks of harassing me again.
    The blower is doing better now after a little work, but the Stihl FS85 trimmer is not.
    So I'll stick to it for now.

    It WAS cranking up just fine. But it would not rev up. It would just choke out and die instead.
    So I went through replacing the fuel delivery lines again.
    I got it back to going, but it was still finicky and would take spells.
    In addition, it would die if tilted on it's side to edge.

    So I converted the fuel lines a bit and went to the heavy Echo style fuel filter.
    This is because the Stihl ones tend to want to float.
    So I figured that might be why it was croaking on me when tilted.
    Well still no dice and the rev issue started to return.

    So I figured I'd replace the carb. (ZAMA)
    But after calling around, nobody had it in stock.
    So I compromised to rebuild the current one and install a new carb kit.

    Once I opened it, I saw that the needle assembly set screw had rusted and no new one was included in the kit. So I cleaned the carb real good and got the rust off the set screw. Afterwards I started installing the kit. I could not get the welch plugs out and did not want to screw anything up. So I installed the new needle assembly and the new screen. Then I replaced the gaskets, diaphrams, ect, and installed a new primer bulb. Then put the carb back on with all new gaskets for the contact surfaces.

    The first thing I noticed is that the new primer bulb would get gas, but would not fill up full like the old one did. So during the process I think I flooded it with the primer bulb. Time for a new spark plug. I put that in and got it running again. But it was short lived and started to take longer and longer for it to warm up enough to rev. In addition it started to get hard to crank again, despite my efforts to be careful with the primer buld.

    Later, I noticed it was starting to leak fuel from the carb. So I figured the new needle valve assembly was not seating properly. So I went back and put the old one in.

    After much effort I got it going again and it ran flawlessly a couple of times. But then it started to leak fuel from the carb again. After noticing this it would not crank. So I began to grasp at straws and decided to slowly adjust the L screw out a bit more. Once I brought it out an extra full turn, again the trimmer cranked and ran fine.

    But when I went to use it again, it was leaking fuel from the carb again. Likewise, it would not crank again. I checked every gasket on the machine and they are all dry also. So now I don't know what else to do.

    Basically I went from a trimmer that would not rev to one that leaks fuel from the carb and doesn't want to start.

    So does anyone else have an idea I might try?
    Or should I put the new carb on order?
  2. lwcmattlifter

    lwcmattlifter LawnSite Senior Member
    from NC
    Posts: 859

    I have a carb from a BR420 i think its a walbro WT-38 on my FS85. That trimmer runs like a champ. It was half the price of the ZAMA plus it has adjustable high and low jets.
  3. Envy Lawn Service

    Envy Lawn Service LawnSite Fanatic
    Posts: 11,062

    That sounds good. I hate those limit caps on the adjustments.
    A cheaper price sounds good too because my dealer wants like $75 to order the ZAMA.
    Now I wonder if that carb would fit my FS85... hummm...

    Probably would, but it's hard to know because they have used like 8 different carbs on the FS85.

    Anyways, after talking to the dealer today and explaining the situation, he says that a new carb would be his next step since the kit didn't help. He says the check valve is probably stuck, which is likely causing the primer bulb to not fill properly and the fuel flooding and leakage.
  4. ed2hess

    ed2hess LawnSite Fanatic
    Posts: 13,197

    I am definitely not an expert on repairs but I do all of ours and I do have two Stihl trimmers. I have had all the problems you describe but have not had to replace the carb to get problems fixed. Are you sure you cleaned the vent hole between the carb and the cylinder, that creates problems. I don't understand the checkvalve statement, not aware of where that device is. I would be concerned that you are simply leaking gas past the needle valve. You did replace it correct? Are you pretty sure you don't have any leaks on the cranshaft seals on both sides? Usually if they are leaking you would see a fuel mess on the cylinder fins. You want to be sure that the bolts that hold the cylinder on are tight, Stihl had problems keeping them tight. These are the four bolts that hold the head on. If they are loose you should see leaking fuel/dirt on the cylinder fins. Hang in there these units have been very good for us even though we are Echo guys.
  5. Envy Lawn Service

    Envy Lawn Service LawnSite Fanatic
    Posts: 11,062


    No, I did not clean any vent hole between the carb and the cylinder. I too have experienced these problems twice and both times the Stihl and Echo stuff went down together. I figured it was the fuel filters and changed those. But it didn't help. So, his time last year I had to go through the fuel delivery on all of it. It all still looked good on the outside. But it was bad. Once I replaced all the lines the problem was solved.

    So naturally when it started again, I thought it was the same thing and went through all of that. So thus far I have not had to replace a carb either. In fact, this is the first time I've had to do a kit.

    I don't really understand the check valve statement either. I guess because maybe that's not a replaceable part. But I will tell you this. I think he may be honest. I say that because of the primer bulb issue. It was beginning to get stubborn, so I replaced it when doing the kit. But once I installed the new one, it just acted like it wasn't pulling in gas despite pumping away on it. In other words, you can't get the bulb to fill like normal.

    Anyways, I think what is happening is that it is pulling fuel but basically loosing it about as fast as it comes in. If I just stand back and do nothing, I can see bubbling through the vents at the bottom and leak down. Maybe that check valve is under there.

    Personally, I also think the major issue is fuel leaking past the needle valve though. But the trouble is I don't understand why.... See, it was not doing this prior to me installing the kit. So I assumed that either something was wrong with the new needle valve assembly or that somehow the gap on the pivot arm was not correct and holding it open. So I figured the sure fire way to fix an issue that wasn't broken before was just to simply put the old needle valve assembly back in it. To my surprise though, it's still doing the same dang thing.

    None of the seals on the engine show any signs of leaking at all and I can't understand why trying to fix one problem created another. I'm almost ready to dig in tomorrow and start replacing the new parts with the old ones one at a time, including the diaphrams ect. I'm lost otherwise.

    But anyways, I would like to ask two questions though. One is how in the heck does Stihl's fuel tank vent? The second is, how do you go about properly removing the welch plugs in the carb? I couldn't get them out and decided to skip them rather than risk screwing something up. There must be a trick.
  6. ed2hess

    ed2hess LawnSite Fanatic
    Posts: 13,197

    Can't help on the plug I don't take that out either. I assume the tank is vented through the gas cap. I think there is some type of back checking on that primer now that I think about it. My models have one adjusting screw on the carb and that always seems flaky to get it adjusted. It is important that the vent hole between the carb and the cylinder is clean. It is always full of junk when I take a unit apart. I think it is in the lower part of the opening.
  7. Envy Lawn Service

    Envy Lawn Service LawnSite Fanatic
    Posts: 11,062


    Thanks a lot. I've almost regained enough patients to go back into it. So I will check that vent later today.
  8. Roger

    Roger LawnSite Fanatic
    Posts: 5,923

    I have four pieces of Stihl gear, but I'm sure none of them are vented through the cap. I've had the same question -- how is the tank vented?

    I make my "not through the cap" comments because the cap is solid, no fuel leaks regardless of position of the equipment. Many times my string trimmer, or hedge clipper are turned so that the fuel cap is on the lowest side, yet it does not leak. I would think a vented cap would leak fuel.

    The other reason for my comment is from my BG85 handheld blower. Usually, when I take off the cap, a hear a bit of hiss. A positive pressure inside the tank is being released. This is especially noticable on a hot day. I don't find the same behavior on my FS85 string trimmer, FC85 edger, or HS80 hedge clipper.

    Back the orignal issue -- any chance of clogged exhaust port? Obviously, the leaking fuel isn't related, but I seemed to remember this issue was an outgrowth of another problem.

    Unless your time is "free," and a new carb is likely to end the problem, minimize your losses and mount a new carb. The cost of the carb will be far less than missing a couple of hours of work, making calls, etc. I hate to not know the source of a problem, but sometimes a sure-fire solution is the most econmical in the long run.
  9. Envy Lawn Service

    Envy Lawn Service LawnSite Fanatic
    Posts: 11,062

    I was involved in a wreck with a drunk driver lastnight and the whole day today was shot. So I wasn't able to get out and just order the new carb as I had intended. So I decided this evening that I would try just once more before morning.

    Someone had told me to try resetting the gap on the needle valve pivot arm for the flooding. So I opened it and 'set the gap' per his specs. It cranked and ran. But the primer bulb still acts funny and there is a bit of hesitation in the high RPM throttle response that can be feathered out.

    But I only ran it for a bit with the engine cover still off. I noticed some smoldering from the muffler as it heated up and assumed it was old flood fuel burning off/out. But the smoldering picked up and then the engine died. I looked it over good and saw wetness on the exhaust manifold gasket between the head and muffler.

    Now I'm not sure what to think anymore.

    Gonna go tinker a bit more with it in the meanwhile.
  10. lwcmattlifter

    lwcmattlifter LawnSite Senior Member
    from NC
    Posts: 859

    Carb is shot, Zama C1Q's are trash and Stihl's biggest fuel delivery failure ever. Don't get me wrong, the rest of the trimmer is high quality but the Zama is the weak spot. I had all the problems you have described and a new carb fixed all. WT-38B will fit FS-85, 90, 50-65. It's $44.51 in J-Thomas. The zama C1Q-S_ _ are all at least $75. Just my.02

    BTW, sorry to hear about the accident, hope you're ok.

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