MS390 / 039 pop up piston

[beaglebriar]

View attachment 102929 View attachment 102930 Here's some pictures of the highway cylinder I had. I'm guessing it looks same. View attachment 102931

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

 

[kkemp]

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

I sold that saw recently . It just didn't impress me . But now I'm curious how it would've been with the popup piston .

 

[beaglebriar]

I sold that saw recently . It just didn't impress me . But now I'm curious how it would've been with the popup piston .

Was the muffler opened up? They're turds until you do that.

Probably my least favorite saw to work on but they're popular so I get to see a lot of them.

 

[kkemp]

Was the muffler opened up? They're turds until you do that.

Probably my least favorite saw to work on but they're popular so I get to see a lot of them.

Muffler was opened up but It seemed to lack torgue. Compression was 145 or so I think when I sold it . I've got another 290 now that's gonna get a cross cylinder and popup piston. It's gonna be all out ported and stuff . Gotta see how fast it'll go.

 

[Terry Syd]

I did some testing on the muffler mod. It is the outer cover that is the bottle neck for flow. You can test it yourself by trying the cover on and off.

I opened up the areas around the center dimpled area so that the muffler wasn't loud. Then I spent a fair bit of time with a butane torch and a ball peen hammer making the outer lid flow better.

To get the largest opening for the lid, trim the side of the cover from the opening down to the bolt flange.

 

[beaglebriar]

If this one doesn't run the way I hope it will I'll go back to the 310 cylinder.

 

[Terry Syd]

It's gonna be all out ported and stuff . Gotta see how fast it'll go.

If you don't want to go through the process of grafting a 660 carb on the saw, you can mod the existing carb to get the same torque and throttle response.

If you don't want to go through the whole process of blocking off the EPA circuit, you can just drill the auxiliary jet in the low speed circuit. You will need a set of micro-drills and a pin vise to do it.

I think I took mine out to .35mm, but I had also blocked off the EPA circuit.

If you had two carbs to work on you can be more confident that you got the right size jet. Stock size is .25mm - take one of the carbs out to .3mm and the other out to .35mm. Test and compare. If the .35mm works better, then take the .3mm carb out to .4mm and test again.

 

[94BULLITT]

The keys I have measured for 044/440, 046/460 and 066/660 are usually .078.

The integral flywheel keys I have measured were about .140 (362 C, etc).

Never seen a key as thin as .060, what saw is that from?

I was wrong about the key size. I was thinking 1/3 of the key was .020, but it is not too far off.

The key on the 290 is .110, so a 1/3 would be .036.

 

[MustangMike]

What saw is that key from?

 

[94BULLITT]

What saw is that key from?

It fits all pro stihls.

Sent from my SM-G950U using Tapatalk

 

[MustangMike]

Your calipers must be different than mine.

The 309 Huztl I got was open chamber, that closed one looks nice!

I thought it was a bit anemic, but I'm used to ported pro saws. The guy I sold it to loves it. Had muff mod + timing advance.

 

[Terry Syd]

I thought it was a bit anemic,

However, if you had added a nylon mesh air filter it would have made a fair bit more top end power - and if you had re-drilled the carb you would have had more 'grunt' and mid-range power.

Cheap mods to a cheap saw.

 

[beaglebriar]

Started rebuilding the 310 today with a Hyway cylinder and the Cross piston.

The cylinder looks quite nice and is a closed port variation. Squish was right at .029 and the port heights measured the same as the stock 310 cylinder.

I'll get some timing numbers tomorrow before it goes back together. Just cleaned up the ports a little on the Hyway, no widening.

Timing 103/123/80 ....not bad

 

[X 66 stang347 X]

I've got a few HD carbs if anyone wants to drill on one

 

[Terry Syd]

I just checked on micro drills and a pin vise. Here's one from Australian Ebay

https://www.ebay.com.au/itm/Mini-Je...155515&hash=item211a468654:g:FBoAAOSwcUBYIuFh

The micro drills are a good addition to your tool box. I've used the small drills on a few projects.

There's a new pin vise I see being sold that twists as the top is pushed down. I've never tried that vise, so I don't know if they work.

 

[RI Chevy]

What model HD carbs?

 

[Frank bierce]

Has anyone posted any videos of modding carbs? I may have to do some searching.

 

[X 66 stang347 X]

What model HD carbs?

I'll look tomorrow. I think a Hd16 and Hd22b maybe

 

[beaglebriar]

The 310 is back together. Hopefully get some run time on it tomorrow.

 

[Terry Syd]

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.