290-390 Conversion / Any speciality tools needed??

[Terry Syd]

I put a 460 carb on my 390 saw. The jet I drilled out was the EPA limiting jet on the low speed circuit. The jet is .25mm - just drill it out big enough that it doesn't limit the low speed circuit. Probably the smallest drill in your drill set will work. The jet is very soft, like it was made to be drilled out. It doesn't take much effort to drill through it.

It's an easy mod, drill it out and then a straight bolt on.

 

[67L36Driver]

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Just not like whoever "plugged" this Husq 455 Rancher decomp, i got it runnin again but a 1" bolt and JB-Weld doesn't work as a decomp plug replacement lol

Bubba must have been on his second twelve pack.

 

[HusqyStihl]

Bubba must have been on his second twelve pack.

I'd have to agree, he did manage to plug up the saw though, all fixed up except where for the custom piston stop and globs of hardened JB-Weld on the top of the piston. What they call that? A pop-up piston?

 

[Paragon Builder]

I put a 460 carb on my 390 saw. The jet I drilled out was the EPA limiting jet on the low speed circuit. The jet is .25mm - just drill it out big enough that it doesn't limit the low speed circuit. Probably the smallest drill in your drill set will work. The jet is very soft, like it was made to be drilled out. It doesn't take much effort to drill through it.

It's an easy mod, drill it out and then a straight bolt on.

Do you have a pic of the jet that needs to be drilled Terry?

 

[Terry Syd]

Crikey, I wish I had taken a picture before I put it on the saw.

I liked the 460 carb as it had the new larger 17.45mm venturi with the discharge nozzle offset to the side - it should flow better than the old style venturi.

There are two jets in the carb. One of them is in line/close to the low speed needle - that is the small jet that needs to be drilled out. There is a second jet that flows in parallel with the high speed needle. When you bump up the flow in the low speed circuit, you have to lean out the high speed circuit. On my saw, I had about 1/4 turn left of adjustment before I ran out of high speed needle. I cut at 2,000 ft, however if I was to cut at a higher altitude, I might have to block off that extra high speed jet in order to be able to tune with the needle. Your mileage may vary. - A dab of GB Weld over the extra main jet blocks it off and allows you to use the needle to set the tune.

 

[HusqyStihl]

Do you have a pic of the jet that needs to be drilled Terry?

Let me know if you can find me one of these for the price you mentioned. Also looking for a used or new but someone doesn't use anymore, and could benefit from a couple bucks, "Tree Climbers Companion" book. Im in no hurry, just thought it'd be a good read if someones got one stashed and no need for it anymore..

Thanks ~Moose

 

[Paragon Builder]

Let me know if you can find me one of these for the price you mentioned.

Thanks ~Moose

It's still available. Send me your address and I'll have it shipped to you.

 

[Paragon Builder]

Crikey, I wish I had taken a picture before I put it on the saw.

I liked the 460 carb as it had the new larger 17.45mm venturi with the discharge nozzle offset to the side - it should flow better than the old style venturi.

There are two jets in the carb. One of them is in line/close to the low speed needle - that is the small jet that needs to be drilled out. There is a second jet that flows in parallel with the high speed needle. When you bump up the flow in the low speed circuit, you have to lean out the high speed circuit. On my saw, I had about 1/4 turn left of adjustment before I ran out of high speed needle. I cut at 2,000 ft, however if I was to cut at a higher altitude, I might have to block off that extra high speed jet in order to be able to tune with the needle. Your mileage may vary. - A dab of GB Weld over the extra main jet blocks it off and allows you to use the needle to set the tune.

Thanks Terry, that should be enough info to do it. Would this be the same on other EPA walbro carbs? Worth doing on other saws?

 

[Paragon Builder]

It's still available. Send me your address and I'll have it shipped to you.

Oh and it's an aftermarket carb.

 

[71dart]

I just got my 039 p/c kit to put in the scored 029. I went with the NWP unassembled kit from baileys and it looks nice. Nothing really to complain about. I do have some caber rings that I'm gonna use.
I wanted to reuse the oem piston pin c-clips but the oem clips measure (thickness of the clip wire) .032" while the NWP clips measure .039". I've seen the aftermath of AM clips letting go but on the other hand it has to fit. Hmmmmm....

 

[HusqyStihl]

I think i did the same thing, the aftermarket kits clips didn't wanna sit right and the originals were still springy enough to pop right in but stiff enough to stay there. Good luck, fun swap. I gotta get 2 other 290's swapped after a couple of Husqies i gotta go through

 

[Terry Syd]

Thanks Terry, that should be enough info to do it. Would this be the same on other EPA walbro carbs? Worth doing on other saws?

I can't speak for all EPA Walbro carbs, but if a carb has the limiter jet on the low speed circuit, then yes it will work. However, bumping up the flow in the low speed circuit is limited by the way the carb is drilled. You can only go so far with tweaking the needle before you end up with a rough idle.

Drilling the throttle plate will allow you to lean out the idle a bit more, but the real solution is to pull the welch plug and re-drill the air bleed holes.

I mentioned the sizes of various air bleed holes in Walbros in the 7900 carb upgrade thread. The 460 carb has a good configuration and any of the other Walbro HD carbs can be drilled to those specs.

I'm presently working on a cheap Chinese saw that has a small HDA on it. I may end up re-drilling the carb and re-positioning the forward bleed hole a bit further forward so that the fuel flow comes in more progressively. It is drilled with the bleed holes side by side and is already very rich off of idle. If the forward hole is drilled at an angle (like the HD carbs) then I should be able to bump up the flow and still get good throttle response.

Reworking the Zamas is easy. However, the Walbros require the removal of the welch plug each time you want to try another mod. Get a least a dozen new welch plugs before you even start...

 

[Terry Syd]

I got lazy with the HDA carb. I had opened up the low speed needle until it was pig rich (and giving good low end torque) and was then thinking about re-drilling it to lean out the idle and improve the response. Then I looked at the metering spring and saw it was a fairly light spring. Hmm, maybe I can find a stronger spring that will ramp in the fuel slower.

I've got a selection of Zama springs that would fit the carb. I put in the strongest spring I could find and started it up.

Yee ha! The longer, stronger wound spring leaned out the idle and ramped in the fuel slower. I had to turn down the idle screw because it leaned out the idle so much. The saw has nice acceleration.

The spring I put in probably has 3-4 times the seat pressure of the stock spring. It was so strong I was wondering if the saw would even start.

If you're tuning a carb, I would suggest getting a selection of springs. There is a Walbro kit that has all the different springs in it, I forget who was selling it on the forum, but if you're working on various saws, it would be nice to have handy.

 

[HusqyStihl]

Anyone have a spare MS290 muffler front plate layin around they don't have a need for? cut a little too much off the front of mine and set the log on fire yesterday. Not the muffler or screen, just the front plate that directs the exhaust to the side, i went all out last year and straight shot it right out the front and now after the 390 swap i had to pull another plate i had off my other 290 and mount it on. never had an issue until i swapped to 390 top-end. now she's cookin!

Guess the 390 top swap makes this saw on fiiii-ya!! gonna have to check around online when i get home to see if that can be ordered seperately or i gotta buy an entire muffler setup...

 

[HusqyStihl]

might as well throw my MM pic on there as well, see the tiny hole i placed in the dimpled area... hard to see but made a big difference

Neighbor came over the other day... "Damn man, sounds like you got the big saws out on this pile of maple"

I sure do! lol He'll be back over with his 290 for some upgrades at some point he tells me

 

[Cope1024]

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Anyone have a spare MS290 muffler front plate layin around they don't have a need for? cut a little too much off the front of mine and set the log on fire yesterday. Not the muffler or screen, just the front plate that directs the exhaust to the side, i went all out last year and straight shot it right out the front and now after the 390 swap i had to pull another plate i had off my other 290 and mount it on. never had an issue until i swapped to 390 top-end. now she's cookin!

Guess the 390 top swap makes this saw on fiiii-ya!! gonna have to check around online when i get home to see if that can be ordered seperately or i gotta buy an entire muffler setup...

You can buy just the muffler body. I'll send you the IPL for the saw.

 

[fearofpavement]

That deflector plate is available. Not sure I have an extras but I can check. They often don't come with a new muffler and if the saw was missing a muffler then you need the muffler, bolts, nuts, cover plate, gasket, etc. It's a lot of parts...

 

[HusqyStihl]

All my 2 & 390's have all the parts to mufflers. Just the one top plate i cut open in the front is where i went wrong. So ill just have to order another front plate.

Ive got all screens, muffler bodies, nuts, bolts, washers...etc. just got carried away cutting into the front plate lol