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  • Homelite saw

    In 1989 I bought what I thought was a new Homelite 550 chainsaw. I used it once in 1990 for a couple tanks of gas, again in about 1993 for a couple of minutes and not again until spring of 2004. I had a little trouble starting it last spring but eventually it lit up and I got most of my sawing done before the oil lines gave out. I replaced all the oil lines and the fuel line and tried to put it to work doing a lot of clearing last summer. It ran long enough to fell a couple of 24 inch locust trees and then slowed way down and quit. I discovered this winter when I started checking things out that the piston had melted down. To make a long story short, I found a new piston, reassembled the saw and it started right up and SEEMED to run OK. Now, here's the rub: the engine will rev all the way up but then drops right back down to low rpm and picks back up...continuously... off and on off and on. I discovered this quite by accident: once I got it running I was revving it up (goosing the throttle) but when I went to set the high speed jet I noticed I couldn't keep engine rpm's long enough to get an approximate setting. If I hold the throttle wide open, the engine revs way up, dies back, revs up, on and on. I've checked the obvious: fuel filter, tank cap vent, pinched fuel line, carb inlet screen, etc. I'm not sure the problem is carburetion, although I thought so at first. Last bit of info: the saw cuts fine and does not stall under load! Can't believe the ignition module incorporates a rev limiter and the Walbro carb doesn't have anything unusual about it. Could the original saw design incorporate a feature to keep the saw from over revving under no load and if so: what is the feature? I hate to sign off on the overhaul and have the saw fail me next time I need it. Thanks

  • #2
    Did your replace the crank seals during your rebuild?
    please visit my webpage:
    http://motorworks88.webs.com/

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    • #3
      Yes, replaced crank seals, and sealed crankcase halves upon reassembly. Also put a kit in the Walbro, replaced ignition module and coil and spark plug.

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      • #4
        I have an old Poulan that acts like that. It must be under load to set the high speed jet. Adjust the jet, take a cut and try it again until it runs like you want it to under load.
        Hope this helps.
        John Burchett
        in Byng OK

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        • #5
          Col....USUALLY, when a saw runs like that, it usually means it's sucking air somewhere.
          They also run almost as you say when they get really hot and the fuel boils in the tank. This is a common problem with smaller saws. I'm not sure what size yours is. If it runs better when cool this could be part of the problem.
          Some saws have a "winter kit" on them that closes off part of the airflow around the head. If you run one with the kit still installed it could be running hot after you use it for quite awhile under heavy load.
          Russ
          I have tools I don't even know I own...

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          • #6
            Sounds like your diaphragm is shot.
            Len

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            • #7
              Col Mckee,

              I agree with QSIMDO that the diaphragm is the problem or at least part of the problem. I have a Homelite XL that I got in the early 70’s and its diaphragm will get microscopic holes in it. Runs terrible until I replace it.

              One other thing that I was wondering about: These older two cycle engines were made to use leaded fuel. What effect does burning non-leaded fuel have on it?
              ____________________________________

              [This message has been edited by Mike Burdick (edited 05-02-2005).]

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              • #8
                New diaphragm was included in the Walbro (carb) kit. Usually, I've found, when a 2 stroke sucks air it won't ever rev up all the way. Mine will rev all the way but then just shuts down (like the switch got shut off or it's out of fuel) and then catches itself and starts the cycle over again. A 550 is a BIG saw - much larger than an XL which I also have. Instructions say to use clean unleaded fuel so we can rule that out. This saw is nearly new:less than 5 hours TOTAL run time. I'm not sure what caused the meltdown last summer. I suspect that it was damaged before I bought it and the shop sold it as new. I haven't worked it since the overhaul so don't know how it will perform, but something is surely amiss. Thanks.

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                • #9
                  "piston had melted down"
                  A piston melt down can be caused by too lean a mix,which leads me to believe (along with your saws present problems " rev all the way up but then drops right back down to low rpm and picks back up...continuously... off and on off" ) that you have an air leak somewhere.
                  Did you find the reason your piston melted or did you just replace it?
                  Do a leak down test on the unit to make sure your crankcase and oil seals are not leaking.
                  please visit my webpage:
                  http://motorworks88.webs.com/

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                  • #10
                    Did you replace the fuel lines and or check old one to see if it has a small crack or leak?
                    mark costello-Low speed steel

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                    • #11
                      Col, sounds like you have been pretty thorough, but you didn't mention the line and filter inside the tank. Did you check those? If they checked out I would go back to the carb and do some more checking. James

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                      • #12
                        I did not discover the reason for meltdown. When the saw quit, it just shut off. I had been having trouble with it running out of gas (or so I thought) and after refueling several times in rapid succession, I realized that it wasn't getting enough fuel. About that time it quit, so I used another saw. I discovered tank vent was dissolved (from age, I thought)and replaced it. Couldn't get the saw to even pop, so I replaced ignition components one by one and still not even a pop. Rebuilt carburetor and replaced rubber carb boot and still not a pop. Finally rigged coil using test leads and determined I had good spark. Next step was splitting crankcase at which time I discovered piston failure. I never imagined a saw with so little run time could go down, but never gave too much thought as to why. I remember buying the saw from a dealer and while it was new, it had been run. I supposed that maybe it had been a warranty return because I got a good price. When I tore the saw down this last winter, I got the impression that I wasn't the first one inside the saw. I guess I attributed failure to original user maybe running it on straight gas and locking it up and the dealer throwing it back together. At any rate, it still ain't right. How does one perform a leak down test? Suck on the line to the fuel pump diaphragm while the piston is at BDC? A clue, please, from Motorworks. I did replace the fuel line from the tank, btw.

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                        • #13
                          Col
                          When I was at this (God help me!!)
                          I had a leak down test kit for Jonsered/Husky/Poulan.(same saws different name ).
                          First you remove the Carb and muffler.
                          There was a plate with a rubber backing to block off the muffle hole or exhaust and another plate with a pipe in it to block off the carb hole or intake.
                          These were not fancy. You could quickly turn them out on your mill or lathe.Put a small fitting in the plate you plan to use to cover the intake that will take a small hose.
                          By using a small pump (supplied with the kit, but again have a look around as to what may be available BUT low presure max 15 psi) you would pump air (approx 10 psi) into the crankcase via the pipe in the intake block cover.
                          The crankcase should hold pressure.
                          Using WD-40 you can spray around the seals and case to check for leaks.
                          During my time at it I did find that even new seals would sometimes leak.

                          ? Did you clean all the AL off the cylinder wall.The walls are usually much harded then the pistons and if a piston melts there is usually AL build up on the wall.
                          Acid used to clean up cement will "cut through" the AL but be careful.
                          Another thing to remember. Never use gas line anti-freeze in any two cycle engine.
                          Changes the temperature inside the cylinder during combustion (much hotter).
                          Last point:
                          Dealer sometimes run demos and it is possible it got straight gas during start up in the shop.In my shop (years ago when I was at it) we only kept MIXED gas on hand. That way there was no "mix up" The worst thing that could happen was someone getting a mower back that smoked alittle!!
                          good luck
                          eddie
                          please visit my webpage:
                          http://motorworks88.webs.com/

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                          • #14
                            Air leak!!! Run for the hills! It's gonna blow!

                            This sounds so typical of an air leak. A pretty big one at that. Probably crank bearigs. The crank seals are sealing long enough to start and rev, then the sloppy bearings allows the crank to move enough to break the seal. I've seen this in chain saws and this same symptom appeard in several of my dirtbikes (also 2 strokes). Fresh crank bearings and seals always fixed the problem.

                            A melted piston == lean out or preigniton. Either one will destroy a 2 stoke pistion in seconds. You absolutely have to figure out why it melted in the first place. A leak down test, as others have stated, is a good place to start. But a lot of times, it isn't conlusive. You need to be able to try to move the crank and that is sometimes a problem with pressure in the crankcase.

                            I've run several Homelite 550's for years and have always gotten good service from them. However, sometimes bad things happen (Bad fuel mix, no fuel mix, crappy gas, etc...) and a cylinder, piston and/or a crank get wiped in serious double time. You can take a brand new saw and total it inside 2 minutes flat.

                            I end up keeping the whole family's boat motors, chain saws, weed trimmers, and leaf blowers going. So this sure does sound like crack bearings to me.



                            ------------------
                            That's my story and I'm sticking to it...
                            That\'s my story and I\'m sticking to it...

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                            • #15
                              Being a plumber by trade, I have a gauge and pump to pressurize crankcase, and I can fabricate an adapter and seal the muffler port. Then, are you saying, to wiggle the hell out of crankshaft to see if I can create leak at (remember, I replaced crankshaft seals)new seals? I can easily visualize seals not sealing with sloppy bearings, but I don't want to spend a lot of time with a leakdown test if I can't reproduce leak(s) by wiggling...which I doubt. Howesomever, I guess the leakdown would eliminate all but crank bearings so that would seem the logical place to start. I did not, btw, clean the cylinder bore, as it seemed pretty good visually, but I suppose if I tear it down, I should double check. Are you saying to use HCl (as in muriatic)? Also, is there a way to determine bad crank bearings by measurement of end or side play and if so, what are the parameters? Thanks again for the input.

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