MS390 / 039 pop up piston

[Terry Syd]

Nope, but after I get the coil, tear into the saw and put it back together - I expect I'll have a drink...

 

[Adirondackstihl]

Saw is super easy to work on mang!

 

[Fruecrue]

Some of the coil wires can be separated from the coil and the plug end can also be removed to feed the wire through.

 

[Terry Syd]

Hell, you're right! I never thought about disconnecting the plug wire and feeding it down to the coil. - Clever, nice lateral thinking!

 

[Terry Syd]

I ended up taking off the plug cap and pulling the wire out the bottom. While checking it out to see how hard it was going to be to get another one back in, I found a 'notch' in the high tension lead. It appears to be from rubbing against something and had worn down to the copper core.

I am going to have to disassemble the saw anyway to find out what caused it and then work out a fix so it doesn't happen again.

(Did I mention I hate working on these saws?)

 

[Czed]

I ended up taking off the plug cap and pulling the wire out the bottom. While checking it out to see how hard it was going to be to get another one back in, I found a 'notch' in the high tension lead. It appears to be from rubbing against something and had worn down to the copper core.

I am going to have to disassemble the saw anyway to find out what caused it and then work out a fix so it doesn't happen again.

(Did I mention I hate working on these saws?)

They are cake to fix
after you do a few.

 

[Terry Syd]

I'm already on first name basis with the nuts and bolts. Each time I put this thing back together I sigh and think, 'That's it, this thing is NEVER coming apart again.'

 

[Lightning Performance]

I'm already on first name basis with the nuts and bolts. Each time I put this thing back together I sigh and think, 'That's it, this thing is NEVER coming apart again.'

You want complicated do a twin overhead turbo audi timing arrangement.

 

[Terry Syd]

Yeah, I hear what you're saying, there's a lot more complicated engines to work on. It's just this thing puzzles me (Superior German engineering?). I despise the way the wires and impulse line have to be pulled through the plastic.

That said, they can be made to make 'respectable' power, if you are willing to do the work. The air filter is a joke as is the ignition timing, but fixing it up is all do-able.

It is made for 'Happy Homeowner' who beats the crap out of saws. Perhaps that's why it has that strong cradle around it and all the high impact plastic. However, 'Happy' still manages to destroy these things.

Stihl sold and still sells heaps of these things and 'Happy' provides a ready supply of used saws for guys to rebuild. - I've rebuilt one, as a courtesy, I'll let you guys rebuild the rest.

 

[Lightning Performance]

Clammys will rule home owners market because of the AV.

 

[a. palmer jr.]

If every 390 is like mine I don't know why anyone would want a pop up piston. Mine already feels like an 044 when you pull the rope..

 

[Terry Syd]

A decomp is your friend. Which brings up a small problem I've had after installing the pop-up, it triggers the decomp too early. I've had a few kick-backs and ruined a few of the plastic starter pawls.

I'm in the process of opening up the hole on the decomp to fix the problem. I'm taking it .5mm at a time. I think I'm getting close, I'll post the final size when I find out what works.

Before installing the pop-up, the saw was a just 'pull and go', no starter drill necessary. I intend to get it back that way.

 

[Terry Syd]

I ended up with a 1.1mm hole in the stock de-comp. That works on my Huztl jug with the gaskets removed from both the de-comp and spark plug. I'll have to see if I need to go any further if it starts to act up after it gets a bit dirty.

With the new coil, the saw is back to being an easy starter, just 'pull and go'.

I also started having problems with the Zama (I think it is the main discharge nozzle), so I put the Walbro back on and fixed the choke issue. It just needed a bit of GB Weld on the actuating arm to compensate for the wear on the plastic. Now the choke closes all the way.

I want to get the idle a bit leaner, but I'll wait until I do some cutting to see how it is performing. I think I might take the forward air bleed hole out to the next size.

Hopefully, I will NEVER take this saw apart again...

 

[Terry Syd]

After using the saw for a while, I started getting the de-comp closing a bit early. So, out came the micro drills and I opened the hole out to 1.2mm. So far so good.

That increase in the size of the de-comp hole is quite substantial over the stock .6mm hole. The increase in compression with the pop-up piston is deceptive.

By the way, I was given the ultimate complement for my 029 'Sleeper' a while back. I went out cutting with a mate and put the saw in the back of his truck. I said, "That's my $50 saw" and then he said, "It looks like it, does it even run?"

 

[Terry Syd]

I bought my cylinder kit from Hutzl and ever since they have been sending me updates. I just saw this 390 kit for US$26.50

https://www.huztl.net/Aftermarket-S...1216-1127-030-0402-1127-021-2500-p368071.html

Crikey, piston, rings, jug, crank, seals - virtually a complete rebuild on the whole engine. I don't think I could get an OEM wrist pin over here in Oz for that price. - It's like reading an advertisement from some sort of 'alternative universe'.

 

[MustangMike]

Always check the shipping costs, sometimes they far exceed the cost of the item!

 

[Terry Syd]

LOL, I just went back to check the shipping and now the price is up to US$37.09. It would still be a deal in Oz.

 

[MustangMike]

If that is a bid price, and not a buy it now price, it means nothing!

 

[Terry Syd]

Now it is down to US$31.79. Bugger if I know how they set their prices, but it appears to be a 'buy it now' price. Weird how the price can keep fluctuating.

 

[MustangMike]

Sometimes, the same item is listed several times at different prices by different sellers, and availability keeps changing.