Stihl 039 Rebuild

[Brewz]

Cheers mate, I actually clicked after I posted that and guessed you ment the MS460 carb. I will order one tonight and it should compliment my dual port muffler well.

Now when you mention drilling out the low speed jet, that sounds easy to get wrong.
Are there instructions anywhere on how to do it properly?

 

[Brewz]

Further question on the 460 carb



I measured the one on my 039 and it has a 22mm opening as well. Where does the advantage come from?

 

[Terry Syd]

The venturi (the smallest diameter of the carb) will be 17.45mm rather than 16.67mm. However, the biggest advantage is in the jetting of the carb. The air bleed holes are larger and allow you to run more fuel through the low speed circuit.

When you get the carb, post a picture of the inside of the carb (the 'wet side' with the metering lever) and I'll tell you which jet to drill out. It should be very thin and you could just twist a drill in it by hand. It is only used as a 'limiter' to the fuel flow in the low speed circuit. Once you remove the restriction, you can dial in the low speed circuit with the needle.

 

[Brewz]

Copy that, I have a 460 carb on the way!

might find a bit of timber to do some timed cuts in before I get it so I can be sure its made a difference.

 

[tree_chomper]

I just got done rebuilding 3 390s and a 290 and 310 come tomorrow. I like the 460 carb idea. I always port the muffler on this series of saw. Much better performance

 

[Brewz]

Yeah they really respond to more airflow.

Once I added the 2nd port on the side of the muffler, I would say it wound up to max revs 20% faster than the base muffler mod.
You notice the difference in the cut too, with them holding higher revs. They feel like a bigger saw.

Sound better too

 

[Brewz]

When you get the carb, post a picture of the inside of the carb (the 'wet side' with the metering lever) and I'll tell you which jet to drill out. It should be very thin and you could just twist a drill in it by hand. It is only used as a 'limiter' to the fuel flow in the low speed circuit. Once you remove the restriction, you can dial in the low speed circuit with the needle.

Ok..... I have the carb.

Would now like to mod it and fit it and give it a go
Where do I drill?

Edit: correct photo

 

[Terry Syd]

Take the cover off the 'wet side' of the carb where the metering lever is. Post a picture and I should be able to direct you to the jet to drill.

 

[Brewz]

Haha I posted up the pics of the carb then read your message again

Faceplam

Pic is above.
I really appreciate your help.

 

[Terry Syd]

OK, the top brass jet with the slot screw driver screw is for the main jet (high speed needle) circuit. Don't worry about that jet unless you can't tune the high speed needle. In which case you can just unscrew it and plug it up with some GB Weld. Then you should be able to adjust the high speed needle.

The jet you want to drill is the one next to the aluminium cover for the low speed circuit. It is presently limited at .25mm. You want to just drill it out. You don't need to put the drill bit in a drill, you can probably just twist the drill through the thin copper 'jet' material. Take the smallest drill you have (say 1mm drill) and twist it through the thin copper EPA limiter jet. There's no need to worry about the size of the drill, just drill the limiter out.

Once you have it opened up, then you can set the low speed circuit to the way you want it. Put it all back together and tune it.

 

[Brewz]

Legend!

Hi ho.... Hi ho.... its off to drill i go.......

Is this the same on most carbs?
I am porting an 026 and dont want to have to hack the saw to install an 044 carb

 

[Terry Syd]

Here's another hint. The air filter on these saws is pathetic. Sure they have the 'compensator' for when the filter gets dirty, but that just means they aren't flowing as much air as you want. Although you have a bigger venturi, that doesn't mean you are going to have more flow. If the air filter is the restriction, then that is what you are going to have to address next.

After you get the engine running the way you want, pull the filter off and see if the revs increase. If they do, then you may want to build yourself a better flowing air filter (like I did).

 

[Brewz]

Drilled the limiter to 1mm
I dont have a filter that will fit the compensator so I swapped the top of my 039 carb onto the top of the 460 carb.
Fitted it up, set L to 1/2 turn and H to 1 turn and pulled the cord

it idles PERFECT.
I cant give it a rev as the kids are in bed and the neighbors have a baby, so I will be a considerate bloke and run it up tomorrow. Its a bit loud





The carb had an issue with the choke plate arm. It was bent and would stick and not open back up completely by its self.
Pulled it apart and straitened it out, and it now functions perfectly.

NOW...... your not going to hold out on me on this air filter mod are you?
Is it like this?

 

[Terry Syd]

The carb drilling looks great, it should work well. You'll find out when you stick it in some big wood and drag the revs down, you should have more torque down low - and better throttle response.

That series of saws has an insert that blocks off the air flow from the hot air going past the cylinder, probably good if your in a cold climate and you need to keep from icing up the carb. However, in Oz all you are doing is decreasing the air density going into the carb. You at least have the valve to cut off the hot air flow, my $50 crap saw didn't have that and I GB Welded a piece of beer can in the slot.

The air filter mod I made was to strip the felt off an old 029 filter (no compensator) and use some thin filter foam over the nylon filter mesh with a layer of cotton from an old flannel shirt as the filter. I probably increased the area of filtration by 100%, maybe more. It not only flows better, but does a better job of filtering.

 

[Brewz]

Yeah I set all my saws to summer mode with the hot/cold inserts.... that's a given!

Engines need cool clean air.

What I would love to do is make an adapter that takes a filter from an 066

 

[Terry Syd]

If you haven't done the timing trick, you really need to do it. As I indicated previously this series of saws has a factory tolerance of 23.5 degrees to 28.5 degrees BTDC. That is a shocking admission from Stihl about their quality control - 5 degrees tolerance in ignition timing.

With the loose factory specs, some of these saws can take an increase of 8 degrees. Yours may only be 4 degrees, but you will notice a big difference even at that adjustment - and at 8 degrees it will be night and day.

Doing the carb mod first is the best idea as you can dial in the ignition timing to fit the fuel mixture.

 

[Brewz]

Well I have a degree wheel I have made for my 026 porting.
How do I accurately measure the ignition timing?
It would be good to get some fixed figures and modify accurately, not just file the key and hope

Edit: Forgot to ask..... where is the timing at an optimal spot?

 

[a. palmer jr.]

I've used a timing light on chainsaws before. You have to mark top dead center and work from there.

 

[Brewz]

Yeah I was just reading up on that.
Question is, is there a way to know where the ignition timing is now if it has a 5* tolerance?
Would be good to know where it is at before advancing it

 

[Terry Syd]

I notched the slots on the coil and ground the threads off the tops of the mounting bolts in order to make the coil 'adjustable'. It gives around 2 degrees of movement.

I can then advance the coil and see if the saw likes the new setting. If it does, then I can take a little off the key to give it another 2 degrees of advance. I can then check by moving the coil if it is too far. If too far, I can shift the coil back 2 degrees.

The 'adjustable' coil allows me to play with the timing and dial it in. If you continue to advance the timing and can't feel any difference, then go back to your last setting. No use pushing extra heat into the engine.

If you increase the size of the slots, you want to put a thin washer under the bolt head to make sure the bolt will adequately hold the coil in position. I didn't do that initially and the coil came loose.