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A Dying Chainsaw's Last Words #1: Carb Rebuild

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Blog entry by woodshopmike posted 04-22-2014 07:36 PM 6633 reads 0 times favorited 13 comments Add to Favorites Watch
no previous part Part 1 of A Dying Chainsaw's Last Words series Part 2: Top End Rebuild »

I figured there’s at least a hand full of people that frequent this site that could be helped out by this article. Who hasn’t had a chainsaw at some point that was giving them a fit?

If you have an older chainsaw, you’ve probably heard it say this before: “Help, Help! cough, umpfh, vrooooommmmm! cough, sputter, death.” I’ll walk you through the steps of bringing a Stihl 026 chainsaw back to life.

Maybe I shouldn’t lead off with this, but my Husquvarna 55 has never given me trouble… Just sayin’.

Alright, some history. The 026 was given to me. Yes, pretty cool, right? It was in a box… In pieces… With enough oil impregnated swarf packed into each nook and cranny to make a dozen toxic candles. The first step was clear. CLEAN!!! Tooth picks, nylon brushes, and a steady supply of compressed air were the tools needed for this project. After replacing the spark plug and putting some fresh gas in the tank, she was purring like a kitten.

Fast forward about a year and things aren’t so dandy. Once the saw would turn over, it would immediately die. Nothing is more frustrating.

So what’s the problem? Well, I had a hunch that the carburetor needed to be rebuilt, so I tore it apart and what do ya know. The diaphragm was torn… This is obviously an issue. Lets hope it runs like a top when I get it back together.

I found my carburetor rebuild kit on ebay for less than $10. If you try getting these parts from your local chainsaw shop… Well lets just say you shouldn’t even bother calling because it will be at least 3 times more expensive.

Rebuilding a carb is pretty straight forward. Keep track of the way things come apart. Catch the spring that wants to go airborne from the needle valve. Give everything a good soak of carb cleaner and then reassemble. Easy, right? Well, just in case you like pictures as much as I do, you’re in for a treat.

Check out the full article on my blog

Thanks for readin’ y’all

-- www.woodshopmike.com, www.woodshopmikestudio.etsy.com



13 comments so far

View Bogeyguy's profile

Bogeyguy

548 posts in 1531 days


#1 posted 04-22-2014 11:30 PM

And if that doesn’t work? LOL. Just trashed an old 16” Craftsmen CS. Had not used it for years. When I dragged it out to try to get it running it was not responding. I removed the side cover and found all the fuel lines had disintegrated. For a minute I thought about returning it to Sears for replacement buuuut I figured after about 30 years they might not want to do an exchange. LOL!

-- Art, Pittsburgh.

View woodshopmike's profile

woodshopmike

222 posts in 1127 days


#2 posted 04-22-2014 11:44 PM

Yeah, they may not really like giving a refund on a 30 year old saw! If the fuel lines were toast it sounds like gas with ethanol was used during it’s life. You’ve probably heard it before, but ethanol eats rubber. Especially the fuel lines in older 2 cycle equipment. It also attracts water into the fuel which doesn’t burn too well :) Drive the extra mile and pay the extra money for ethanol free gas.

I’ll be posting about a complete top end rebuild in a day or so. You can read it first on my blog though!

-- www.woodshopmike.com, www.woodshopmikestudio.etsy.com

View UpstateNYdude's profile

UpstateNYdude

695 posts in 1446 days


#3 posted 04-23-2014 02:41 AM

Maybe the 026 is harder but my 028 took me 20 minutes to rebuild the carb and change the plug and I haven’t had to touch it.

-- Nick, "Choking to death on bacon is like getting murdered by your lover." - JG

View woodshopmike's profile

woodshopmike

222 posts in 1127 days


#4 posted 04-23-2014 01:22 PM

20 minutes isn’t bad! Rebuilding the carb wouldn’t have taken nearly as long if I hadn’t been snapping photos for my blog. The needle valve took the longest to get a decent picture of. That dang thing is a bit small! I had to replace the top end since there was virtually no compression in the saw. Since that, she’s been running great!

-- www.woodshopmike.com, www.woodshopmikestudio.etsy.com

View UpstateNYdude's profile

UpstateNYdude

695 posts in 1446 days


#5 posted 04-24-2014 03:16 PM

Yeah the floats are a PITA in any carb you have to have bite size keebler elf hands in order to fiddle with all the tiny pieces, anyway good luck with your saw I got mine for $50 on CL the guy just hadn’t cleaned the carb and it was all gummed up, that and he had the High/Low adjustments set way out of whack now it screams through anything I throw at it.

-- Nick, "Choking to death on bacon is like getting murdered by your lover." - JG

View woodshopmike's profile

woodshopmike

222 posts in 1127 days


#6 posted 04-24-2014 03:54 PM

Even better would be a keebler elf assistant! I’m still fiddling with the carb adjustments. I’ve started each with 1 turn out and have tinkered enough to get it running smooth with good acceleration, but it lacks enough power to not bog down in a cut. It’s also dying at idle. Suggestions? I’m at the point of waiting until I visit my uncle who has worked on and with chainsaws for a long time.

-- www.woodshopmike.com, www.woodshopmikestudio.etsy.com

View Dallas's profile

Dallas

3599 posts in 1950 days


#7 posted 04-24-2014 04:53 PM

Change that silly fuel filter to an aftermarket version. You might want to change out the fuel lines also. The new fuel lines aren’t bothered by ethanol. Neither is the carb or the primer bulb. I ususally buy 10’ @ $1’ at a time of both sizes, (Works on multiple saws). Check the muffler to see if there is a build up of old crappy fuel. That will allow an engine to start but there wil be no power and it won’t idle. One of my favorite things to do now days is buy junk saws from ebay and CL and yard sales and make them work again.
Not long ago I traded one old 1-10 Mac with no kill switch for a pumpkin crate full of old chainsaws at a pawn shop. I think there were 43 in the box. I, so far, have made 27 run and they have been sold.
Rather than spending time to rebuild a carb I just buy a new one. Usually they are about $20. Fuel filters are about a buck a piece if you buy in bulk.

A piston, pin and ring are only about $30 and if you have low compression, it’s probably best to change everything.
I bored my 50cc Poulan to 52cc giving it a bit more power and correcting some egging I thought I saw.
I also hot rodded it a bit like in the old days by emptying the muffler, With nearly 300 hours on that saw, doing that brought up the power about 15-20%.

-- Improvise.... Adapt...... Overcome!

View woodshopmike's profile

woodshopmike

222 posts in 1127 days


#8 posted 04-24-2014 05:18 PM

Dallas,

Thanks for the tips. I have changed out all of the lines and replaced the original fuel filter. I also checked the muffler just yesterday to look for buildup (b/c i was too dumb to not look closely while I had the whole thing apart)!

I actually went through and completely rebuilt the saw after have worked on the carb. There wasn’t enough compression for it to do anything more than burp when it was turning over. here is the rebuild post. I’m sure you won’t learn anything, but maybe you’ll spot something that I missed…

I’m starting to wonder if I shouldn’t just buy a new carb. It’s against my nature to not keep trying to make something work though :(

I really enjoyed doing the rebuild and am itching to take on another. I’d like to score a big saw I can use for slabbing pieces for my shop built lathe... You’ll understand once you see the thing!

Thanks for the suggestions!

-- www.woodshopmike.com, www.woodshopmikestudio.etsy.com

View Dallas's profile

Dallas

3599 posts in 1950 days


#9 posted 04-24-2014 06:43 PM

Mike, I enjoy building things I want but can’t afford. The lathe is way cool. I want to build one but probably won’t ever do it.
My thoughts on a large band saw would be to build one using tires, wheels drums bearings and axle shafts from a VW front end.

You have the skills and the training and the knowledge to do precision work. Use that and build.

You could even use an old 36 or 40 HP VW engine as the motive power. The old tires would act as the alignment to keep the blades on straight. Pick your size and built it. Personally I want a 36” to 48” throat so I can slab faster and easier and would probably use an Isuzu 4 cylinder diesel from a Thermoking refrigeration unit on a semi trailer, (blown engines are easy to find cheap and for the $400 overhaul kit will last the rest of your life). The big plus is that you can set the engine up for the torque, horsepower and rpm that will deliver your best performance.

With your overhaul there are a few things I would do differently, mostly it looks great. Using a ring compressor, ($10 at O’Rieleys), will help on engine life 1000%. The tip of many screwdrivers is hardened, even cheap ones are made from HSS. Both are harder than that of the piston or the rings. Pistons are aluminum with a coating to allow them to season to the cylinder. the rings are cast iron. Either one of which will score easily with a steel screwdriver blade. You may not see the scoring, but it there nonetheless. Where the metal scored will rub on the cylinder wall and eventually cause another low compression issue.

2 stroke engines are very to work on, but they can be very picky at the same time.

You may not believe it, but for awhile (about 40-45 years), I made a good living rebuilding 2 stroke diesels up to 1000CI per cylinder. SOme were inline two, some V-6, some 16 cylinders. Those were the days, now California has outlawed them in the harbors. Even though there is an upgrade to these engines that will pass every test CARB has, the state of California refuses to change the regulations.

I’m starting to wonder if I shouldn’t just buy a new carb. It’s against my nature to not keep trying to make something work though :(

Edit
I have little luck rebuilding 2 stroke carbs. I found myself putting the 4th kit into one carb and at $10/ea, a new one was a better option.
Believe me, I would much rather rebuild than replace, but it is so much more cost effective when you think of it that way.

-- Improvise.... Adapt...... Overcome!

View woodshopmike's profile

woodshopmike

222 posts in 1127 days


#10 posted 04-25-2014 01:21 PM

Dallas,

I may just have to buy a new carb and be done with it. Question though. I just posted this on the second installment of this serious but who cares!

I was adjusting the carb this morning and tuned the high jet just before the saw starts to burble. I’ve taken the jet really lean and the saw starts to kick, kinda sounds like a backfire. I’ve then enriched the gas mixture so that the RPMs drop off. No where in the range does the saw wind up like it used to. It doesn’t scream and the throttle isn’t anywhere near as responsive as my other saw.

Since you’ve rebuilt one or two of these things :) Here’s my question. I noticed that then I was reassembling the crank case that I could over tighten the screws closest to the crank shaft and that it would bind the crank shaft. I backed them off what I thought was “enough” (I could rotate the CS without much resistance) could this be my issue? I’m just wondering if the saw can’t overcome that little bit of “built in” resistance…

Thanks for the suggestions!

BTW, I had thought about the screwdrivers being hardened so I was uber careful, I totally see what you’re saying though, there very well could be small scratches that will magnify as time goes on.

-- www.woodshopmike.com, www.woodshopmikestudio.etsy.com

View Dallas's profile

Dallas

3599 posts in 1950 days


#11 posted 04-25-2014 02:32 PM

If the recoil seems more difficult to pull than before, the torque could be the problem although I doubt it.

Have you checked that the reed valve didn’t get damaged while the engine was apart?

What is sounds like to me from here is that you may have an intake leak. You’ll never be able to get enough fuel to it because it will always has too much air.

I repaired a weed eater awhile back that would run but die at idle, always ran lean and was a PITA to start when it was warm.
I figured the reed valve was bad so without checking it I ordered a new one. While I was installing I found an o-ring seal that went all around the perimeter of the intake had been misplaced and slipped at the time it was manufactured. That allowed the crank to suck a bit of air and caused all the problems.
I replaced the reed valve anyway since I had it on hand and now the machine starts first pull and winds out at well over 12,000 rpm.
If in doubt, use the old methods we did in my hotrod days—- If you suspect an air leak, get a spray bottle of soapy water and squirt everywhere it could be coming from. If the intake is leaking, the engine will slow down. If the crank compression is leaking it will blow bubbles.

-- Improvise.... Adapt...... Overcome!

View woodshopmike's profile

woodshopmike

222 posts in 1127 days


#12 posted 04-25-2014 03:01 PM

I replaced the reed valve when I rebuilt the carb so I’m pretty sure it is fine.

I’ll try soap and water but I may go ahead and replace the impulse line again. I had a heck of a time getting it installed and may have stretched out the opening where the carb “plugs” in. The carb slips right on there without much fuss so I wonder if I’m getting a leak around that…

-- www.woodshopmike.com, www.woodshopmikestudio.etsy.com

View Dallas's profile

Dallas

3599 posts in 1950 days


#13 posted 04-25-2014 11:25 PM

One thing that just passed through the aging, embalmed, morass of my alcohol engorged brain…...
Every Stihl I have ever tried to adjust the low and high speed needles on had to have been thoroughly warmed up.
Whether it was a weed eater or a chainsaw, if you try to adjust while they are cold, you will be sadly disappointed.
Usually I let them sit and run for a few minutes and then make them do as much work as they can for a while.
Watch the smoke.
At 50:1 you won’t see much. If it’s cold and you goose it, and it smokes, it’s running rich. I like a bit rich to start with. It gives the rings some carbon to use to build up and break in.

Check your compression again. Make sure it’s over 140, (some don’t mind 125, but the lower it is, the harder it is to start and the less power it has). I have a little Homelite that has 60 psi compression. It takes an electric drill to make it start and has almost no power, but it’s the one my wife likes for limbing trees. Once you get it started it will run all day and idle, for no apparent reason. Don’t turn it off, it won’t start again until the next day.
It’s a piece of junk, and it’s the same age as her son….. 38 years old.
She won’t let me give her another one so when this one stops, I try to find parts.

-- Improvise.... Adapt...... Overcome!

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