MS390 / 039 pop up piston

[kkemp]

There seems to be a lack of interest in modding carbs. People just swap a carb, get an improvement and call it good.

This would be a good project for the forum, modding an HD for more power. There are plenty of other saws that use the HD and the concepts could be applied to those other saws.

I tore the 029 apart yesterday. Gawd, I hate working on this saw. After I had the bench covered in parts, I called it a day and had a drink.

It is a miserable rainy day outside and I just don't have the enthusiasm to clean everything up and start putting this POS together - maybe if I have another drink...

I tip my hat to guys that are willing to work on these things.

I'm definitely going to try a hd carb and see what I can make happen, if I can get somebody to walk me through it. I wish there was a carburetor class I'd be all over that. Lol

 

[Terry Syd]

I think the HD can be modded without blocking off the EPA circuit. Drilling out the auxiliary low speed jet essentially bypasses the EPA design and lets the low speed circuit flow more fuel. If that is the case, it becomes an easy mod.

If you get two carbs, I'll walk you through the mod. You can post pictures of what you are doing and the results you get. I'm sure there would be other guys interested in what you are doing.

Once you have the correct size jet, then the modding gets easy for the next one.

 

[blsnelling]

There you go. Don't know if it would be considered a true closed port but it's definitely different..

Yeah, I don't know what to call that abomination. Looks like an open port cylinder that they just threw a couple bridges over.

 

[beaglebriar]

Compression after one heat cycle.

 

[94BULLITT]

It is a semi closed port.

Sent from my SM-G950U using Tapatalk

 

[beaglebriar]

Yeah, I don't know what to call that abomination. Looks like an open port cylinder that they just threw a couple bridges over.

That's what I thought. Don't know if it will hinder or help performance. I'm gonna run this saw against my buddies 390 tomorrow.

 

[blsnelling]

Don't know if it will hinder or help performance.

My thought as well. It's like a closed port with double bridges and an internal divider. Doesn't look like a good design at all.

 

[beaglebriar]

There seems to be a lack of interest in modding carbs. People just swap a carb, get an improvement and call it good.

This would be a good project for the forum, modding an HD for more power. There are plenty of other saws that use the HD and the concepts could be applied to those other saws.

I tore the 029 apart yesterday. Gawd, I hate working on this saw. After I had the bench covered in parts, I called it a day and had a drink.

It is a miserable rainy day outside and I just don't have the enthusiasm to clean everything up and start putting this POS together - maybe if I have another drink...

I tip my hat to guys that are willing to work on these things.

Right there with you Terry. I didn't enjoy rebuilding this saw at all. I did a 041 a few weeks ago that was more enjoyable and that ain't saying much.

 

[kkemp]

My thought as well. It's like a closed port with double bridges and an internal divider. Doesn't look like a good design at all.

Mine was very disappointing to say the least. But more compression may have made a difference.

 

[Fruecrue]

The transfers open with more area than if the divider ran all the way up.

 

[Fruecrue]

Mine was very disappointing to say the least. But more compression may have made a difference.

Do you remember the squish on that one?

 

[kkemp]

Right there with you Terry. I didn't enjoy rebuilding this saw at all. I did a 041 a few weeks ago that was more enjoyable and that ain't saying much.

I don't mind them at all . But I've had probably 10 or so apart . Lots of tricks to learn on them . @Onan18 has a great thread on them. .

 

[kkemp]

Do you remember the squish on that one?

I don't have the notes in front of me but if I recall , .034 or so.

 

[beaglebriar]

I don't mind them at all . But I've had probably 10 or so apart . Lots of tricks to learn on them . @Onan18 has a great thread on them. .

I've worked on a bunch but mostly tune ups, muff mods and oil pump repairs. This was the first complete tear down.

I'd much prefer to build a nice husky anything but ya gotta take the bad with the good I guess.

 

[X 66 stang347 X]

I'm definitely going to try a hd carb and see what I can make happen, if I can get somebody to walk me through it. I wish there was a carburetor class I'd be all over that. Lol

I have a couple breakdowns and illustrations on the carb ports and functions I can post.

 

[kkemp]

I've worked on a bunch but mostly tune ups, muff mods and oil pump repairs. This was the first complete tear down.

I'd much prefer to build a nice husky anything but ya gotta take the bad with the good I guess.

Just about everyone of them I worked on had bad cylinders . I was ready to crush the first one though.

 

[beaglebriar]

My thought as well. It's like a closed port with double bridges and an internal divider. Doesn't look like a good design at all.

I'd be tempted to go in and carve on those bridges a little if it were mine.

As long as I'm reasonably happy with how it runs I'll leave well enough alone.

 

[MustangMike]

I only did one 029 to 390 conversion, so I can say I've done one. I've turned other dead ones away since then.

Rather work on a 044/440, 046/460 or 066/660 anytime. Getting to know those models fairly well, and they are not so tricky! I also like that you can adjust your squish.

Muff mods and timing advances are also much easier!

If I'm not mistaken, the HD-11 has the richest jetting, but they seem to be NLA. They originally came on heated handle 044s. I believe the HD-50 has totally different jetting (the 461 carb), but only my Ported 460 seemed to really like it.

Conversely my Hybrid really liked the HD-11, but most other saws did not really seem to care!

I have HD-16 carbs off 460s followed by A, B or C. I have no idea what the differences are, but if anyone knows, please share.

 

[kkemp]

I only did one 029 to 390 conversion, so I can say I've done one. I've turned other dead ones away since then.

Rather work on a 044/440, 046/460 or 066/660 anytime. Getting to know those models fairly well, and they are not so tricky! I also like that you can adjust your squish.

Muff mods and timing advances are also much easier!

If I'm not mistaken, the HD-11 has the richest jetting, but they seem to be NLA. They originally came on heated handle 044s. I believe the HD-50 has totally different jetting (the 461 carb), but only my Ported 460 seemed to really like it.

Conversely my Hybrid really liked the HD-11, but most other saws did not really seem to care!

I have HD-16 carbs off 460s followed by A, B or C. I have no idea what the differences are, but if anyone knows, please share.[/QUOTE. I would much rather work on any pro style saw . No comparison on which is easier

 

[Terry Syd]

If I'm not mistaken, the HD-11 has the richest jetting, but they seem to be NLA.

That jetting may be in the form of the air bleed/transition holes. In which case, all we need to do to duplicate the carb is to pull the welch plug and measure the sizes of the air bleed holes. - Then drill another carb to those specs and put in a fresh welch plug.

The bigger the air bleed holes are, the more fuel is running through the low speed circuit. The bigger holes allow more air to lean out the idle mixture. Then when the throttle butterfly moves across them, there is less air bleed and the mixture becomes richer.