Stihl 039 Rebuild

[drf255]

Excellent question.

I'd love to know at what point where the magnets hit the coil that actual firing occurs

 

[Brewz]

I ran the saw today.
I cant lean it out enough with the H screw and it runs very rich. I screwed the H needle all the way in and got to about 11000 RPM. I usually tune it to about 12700.
So I am guessing I need to plug the H jet in the top of the carb?

I ran well but guzzled a tank of fuel in no time flat

 

[drf255]

Try it without the air filter.

Many carbs are also not fully H adjustable. There's a portion of the H circuit that's fixed and a portion that's adjustable. I ran into this problem with a ported 036. Couldn't lean it out.

Contrary to what many will say, opening the muffler can actually richen the mix, not lean it out.

Moving more air through the Venturi will also suck more fuel in a lot of cases.

 

[Terry Syd]

Yeah, sometimes that happens with these carb mods that increase the low speed circuit flow. You will have to pull that slot screw jet and plug it. GB Weld works or solder. I run my saw at 2,000' and I only had about 1/4 turn left to tune it, so I plugged that jet. It gave me about 2 turns of tuning.

As mentioned, it may have also been a restrictive air filter. However, if you plug that jet you should be able to tune it. I would definitely check the air filter because that may now be the biggest restriction in the intake.

 

[Brewz]

This morning I plugged the jet and filed a small recess on the bottom side of the butterfly to act as an air bleed that won't suck fuel at idle to try and lean out the idle. It was idling rich and would blow lots of smoke when i revved it up again. I put it all back together, took it out the back and fired it up.

I now have heaps of adjustment and can lean it right out and bring it back just into the rough. Gave me about 12750 rpm at WOT

I fiddled around with combos of LA and L screws to get a nice smooth idle and good throttle response.

Chucked it in my work truck and headed out to my parents farm to run it in some wood.

First test was extreme load test with a 30" 3/8 bar and full comp full chisel chain. Cutting 2 foot thing hard eucalyptus it did it better than it used to when stock but would slow and stall if I really leant on it, which is fair enough. I won't be selling my 066 magnum!

I took this bar off and bolted on a more realistic 20" bar running 3/8 full comp semi chisel chain.
WOW!
The low speed torque was very noticeable with the saw only slowing when buried all the way in timber and me bending the handle swinging on it.

This mod with the 460 carb hasn't made it more powerful over all. Unloaded cut speed is the samebut it has made it much stronger under load when normally the revs would drop and cutting speed would deminish, it now just keeps on keeping on.

$20 well spent!

Thanks for your help Terry.
I might advance the timing a couple % now. Will pop the flywheel and file the key.

 

[Terry Syd]

Yeah, what you experienced with making the low speed circuit richer using a Walbro was what Rich was doing to the Zamas in the '7900 carb upgrade' thread. My attitude is fork the EPA and their fuel sipping low speed circuits, I'd rather have that torque.

Hopefully your saw will turn out to be one of the saws with the lesser 23.5 degree BTDC timing. Then if you dial in the timing you can really go 'WOW'.

EDIT: You may want to check and see if the air filter is restricting the power. Get the saw warm and check the maximum WOT. Then pull the air filter off and see if you can tweak it higher.

 

[Terry Syd]

Oh, and if you really want to get sick about modding this old 039, I noticed that Bailey's has a 20" Narrow Kerf bar (Woodland Pro) that will fit the saw - US$27

Just make sure your saw has the upgraded oil pump with the longer stroke - that chain is gonna fly with an 8 or 9 pin. You may have to go to a 361 clutch drum to play with the pin size.

The lightweight bar completely changes the handling of the saw. It goes from being nose heavy to tail heavy. With both hands supporting the powerhead, it feels like a lighter saw. Couple in the fact that the bar and chain is lighter and easier to move, the saw is nice and nimble to use.

 

[Brewz]

Will play with the timing through the week. It's all packed up now.

I am happy running the 3/8 .063 chain. It's tough and gets the job done.

To be honest, the thought of thinner chain running faster with more torque when cutting firewood in gnarly old hard gum trees makes me nervous.
If I want to cut faster, I will just fire up my 066.

I am after usable power for work, not speed for cutting cookies for YouTube. The 460 carb sure helped with that.
It was a real treat being able to really force the saw into the wood and have it power through as opposed to slow down and bog.

I know your not supposed to cut under heavy pressure but in dead rock hard wood, sometimes you gotta swing on it to get the teeth working, no matter how sharp they are.

 

[Terry Syd]

I am after usable power for work, not speed for cutting cookies for YouTube.

I'm a wood cutter, that's why I wanted the extra torque for doing WORK. The NK bar helps me to do it quicker and with less work. I'm 68 with a bad back and wear TWO back braces when I cut. The lighter saw helps me get the work done.

Here's a couple of other tricks I used on the saw that you might find useful. When I advanced the timing I got to a point where I got some 'kickback'. When it happened out in the bush and the plastic pawl in the starter mechanism failed, I had to use my backup saw. I decided I didn't want it to happen again so I got a 660 coil with a 4 degree retard when starting.

I don't want to go through a 'starter drill' like I would use with a 064, so the 4 degree retard works where I can just pull the starter when ever I want and the thing starts. Again, it was another $20 Chinese purchase, but well worth the money for me.

On the 460 carb the choke valve is set up for a 76cc engine. Since I used the saw so infrequently the inverted wet side of the carb out would drain out and the carb would be dry. It would take about 20 pulls to get the carb primed again. Once it was running for the day, then it was a one pull start. However, I didn't like pulling the damn thing over 20 times to get it to prime, so I used some GB Weld to close off part of the choke cutaway. Now it is 10-12 pulls to prime and I can live with that.

You know how expensive saws are in Oz. I've got about $300 in this ugly POS and it is now my go-to saw. These saws were made for 'happy home owner' who needs a fair bit of slack, like no 'kick back' and low power for longevity. Most of the guys on this forum are familiar with saws and can bring them up to their potential. For an inexpensive saw, they work rather well when set up right.

 

[Brewz]

Mine only took 4 or 5 pulls to turn over dry when I fitted the new carb. After that I have found it a pleasure to start with only a half hearted half pull on the rope to kick it once warm.

I don't want to put any more money into the saw as I have too much in it already but it has been a learning saw and the money I have in it was money well spent.

I noticed considerably more kickback force with the 460 carb and I would happily guess at 30 to 40% power increase from when it was stock with the muffler mod and new piston and caber rings.

I may look into the narrow kerf bar for my 026 pro I am building up to replace the 039 and will probably still sell it.
The only thing that's stopping me is I have grown attached to it during my journey of repair and modification and it would be a shame to sell it on just as it becomes a reliable powerhouse.

Much to consider....... Yeeeees

 

[Brewz]

Decided to leave the timing alone, its strong enough and I cant be bothered now that I have my 026 ported and back together.

While I had the fly wheel off, I noticed that my 2nd attempt at reassembly clamping it with the seals in place was far more successful.
No more leaks after 4 or 5 tanks of fuel.

Compression is noticeably higher now it has several tanks of fuel through it.
There must be something wrong with my compression tester ad it started at 145 psi fresh and mow reads 120psi.
I tried it on my other saws and its reading a good 30+ psi lower on them too.

 

[Terry Syd]

I've never checked my compression, but the saw is stock and probably about like yours. I did remove the washers from under the de-comp and the spark plug to give it a bit more.

Every time I read about someone welding up a pop-up piston I wonder what this thing would run like with 180 psi, but then the cost of the work might add another 50% to the cost of this saw. I couldn't justify that - it's reliable now and works well, I'll just keep the chains sharp.

Do you think the flywheel is still rubbing against the case, or did the new main bearings fix that?

 

[Brewz]

Na its not rubbing any more.
Mine does not have a de-comp but I recon I would want one with more compression.
Its making really good compression that you can feel strongly resist the starter cord and it kicks up really easy.

To be honest, I don't want to push it too hard as I don't think the saw was designed for super horsepower and eventually, something will become a weak link.

With a sharp chain its now quite a weapon that you can lean on in the cut.

 

[a. palmer jr.]

I've got mine all together except I found a sticky clutch I guess weak springs. When the new one arrives I'll take the old one off and replace it then try modding the muffler a bit. I've already put a new chain on it then I'll try to get some pics.

 

[Brewz]

Open that muffler up!
If you don't want a lot more noise, just open it right up around the outside of the baffle, and try and get a drill in to open up the holes in the baffle that lead to the inside of the muffler body.
Once you get the air flowing better, I will recommend Terry's 460 carb mod.
It really makes the 039 cut like a 64cc saw should cut!

 

[tickhound93]

Honestly never tried the 460 carb. But built quite a few 390s that were stout. A 460 carbight be my next purchase for Pure entertainment. I always liked the 390s because so many people hate them. Never spent much time modding them because I have bigger saws, I scarcely can get customer saws and saws for sale ready. I do a muffler mod, crank the flywheel as advanced as it will go and send the saw out the door, some gains, happy customer, and little time. My saws get maintenance and fuel, not all the time I got for them.

 

[Brewz]

Speaking of pictures, I just realized i have not posted any pretty poser pictures of the saw since its rebuild

 

[tickhound93]

Yup. Its an 039, looks good too.

 

[Stihlofadeal64]

Speaking of pictures, I just realized i have not posted any pretty poser pictures of the saw since its rebuild

View attachment 476579

View attachment 476580

SLICK!

 

[a. palmer jr.]

Mine looks similar to that except it says "029" on the top cover because it was converted.