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Post by MC123 on Jun 23, 2018 18:23:35 GMT -5
I'm looking for some help regarding my Homelite 550. I decide to repair my saw that had been sitting for ten years after I broke the chain sprocket/drum while cutting up a 36" diameter oak. After fixing that issue, the saw started with a few pulls but was running real rough, so I rebuilt the Walbro SDC carburetor. I also checked compression since it was blowing smoke out the muffler and got 120 psi. The rebuild fixed the low end idle but the saw is still running rough and smoking at high RPM's. Since I'm not a professional small engine mechanic and my skills for rebuilding carburetors is hit or miss, I bought a NOS carburetor online. I installed it and I'm still having the same issue. The saw doesn't what to run smooth at high RPMs. The plug looks like the saw is running rich and no adjustment to the carburetor external settings seems to work. Is there something that I'm overlooking, maybe an intake air leak, does it sound like it needs piston rings? Any suggestion or ideas will help.
Thanks,
Mark
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Post by sweepleader on Jun 23, 2018 19:58:11 GMT -5
Hi Mark, Welcome to the House of Homelite.
You did not say much about it but when the sprocket broke, did the engine stop abruptly? If so, you may have sheared the flywheel key and thrown the timing off. I don't know much about 550's specifically but that would be a common problem with a sudden engine stop. Others will be along to offer their thoughts too.
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Post by undee70ss on Jun 23, 2018 20:11:10 GMT -5
What does the boot look like? ( rubber tube between carb and engine) There’s a good chance it’s bad and causing a air leak.
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Post by lesorubcheek on Jun 23, 2018 20:19:29 GMT -5
Hello Mark and welcome! Sounds like you know how to adjust 2 stroke carbs, so adjusting the jets is something I assume you're skilled at doing. 550s use a rubber boot, and it's certainly worth considering, but usually if it's torn, it'll cause a lean racing condition. Based on the symptom of smoke, my first guess would be to look at the oiler diaphragm. 450s and 550s used the same diaphragm as the early little XLs and Super 2s. There's a passage to the crankcase for a vac/pressure pulse to work the diaphragm. If it's leaking oil, it'll suck right into the engine, and poof, you have smoke. The oiler is just in front of the clutch with 3 screws holding the cover.
Dan
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Post by 5terrysupersaws on Jun 23, 2018 23:18:55 GMT -5
120 psi is slightly below the optimal performance spec. of 125-155 psi for a 550
A 550-W model will have a spark arrestor screen (as Std. Equip.) behind the muffler cap,
if not clogged or no screen...remove muffler and inspect exh. port,piston/rings/cylinder.
Let us know what you find...pics would be great too.
Al
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Post by MC123 on Jun 25, 2018 17:42:40 GMT -5
Thanks guys for your insight. A quick scenario for what happened when the drum/sprocket broke. The saw never stopped running, the chain just stopped spinning. The part of the drum that the sprocket sits in broke at the weld. I had the muffler off and the cylinder wall looked good. As for being out of time, I have had lawn mowers where I have sheared the keyway off and it doesn't seem like the issue. I may still check, however I think I have a bigger issue. I went to check the oil pump and the diaphragm looked good. Dan, should the spring behind the diaphragm force the diaphragm out? I oiled it up, pushed it in and it pops right back out. So far so good. I push it back in a few more times and it stays in. Is that what it should be doing? Now the big problem, I went to add bar oil and noticed a gas smell in the oil tank. I drained it out and dried the inside of the tank. about two hours later, I noticed a small puddle at the bottom of the tank. I then proceeded to pull all oil lines out of the tank and dried it again. A few hours later, a small puddle. I dried it a third time, left it over night, again another puddle. Now I'm thinking that the two are mixing, which would explain why the saw is smoking. It looks to be more of a weep. I guess I need to figure a way to pressure test the tanks.
Thanks,
Mark
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Post by lesorubcheek on Jun 25, 2018 19:36:45 GMT -5
Mark, well it sounds like you have the situation where the divider between the gas and oil tanks is leaking. There's a thin metal plate that is basically glued in between a section in the tank halves. These have been known to separate. Someone either here at HoH or maybe at arboristsite described how to split the tank and re-seal this. Unfortunately, it's not a normal procedure, but is an option. I'll try to find the post and provide a link. As for the pump, yes, the spring is behind the diaphragm and should push out. If it's stuck in, it may push out with pressure, but should work out if you can get a grip on the metal center section.
Dan
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Post by lesorubcheek on Jun 25, 2018 19:42:00 GMT -5
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Post by MC123 on Jun 26, 2018 20:26:58 GMT -5
Thanks Dan, I can see a glue bead gap at the bottom of the oil tank, which seems to where it's leaking. I'm going to try and reach out to Sawnami and get some more insight, such as what type of glue he used. I don't know when I'm going to tackle this project but I'll post my progress.
Mark
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