HELP! Transfers

[UltraSwine]

Greetings. I'm a year-long lurker, this is the first time I've had a question that isn't answered by a little searching.
Long story short, this is a transfer port question. More or less. I was running an 49mm AM 390 jug on my '04 MS290 and it fried. Now, I am putting the original Mahle 46mm jug back into service. While I have worked the Mahle (290 46mm) jug for squish (chamber,milled base, bearing/seal saddles) the 46mm MS290/029 transfers have me baffled. "390" jug has larger transfers, I get it. In the "390" the primaries (exh side) are slightly larger than the secondaries (int side). No shocker there. But... the 290 jug is different, the primaries are noticably smaller than the secondaries. Why?
After dropping the jug more than 0.040" the transfers will need to be raised. Should I open the primaries more like the secondaries while I'm in there? Or, is there any benefit to having tighter primaries? Open quad port, BTW.
After reading "theories" on this site until my eyes bleed, I can't figure out how it would matter how a saw gets happy with one configuration over another AS LONG AS it gets the air/fuel it requires. But... I'd like to know whether or not primary vs secondary "volume" makes any difference if the engine gets what it wants.
Thanks in advance.

PS, sorry if I posted wrong.

 

[Woodwackr]

Aren’t these open jugs?

 

[UltraSwine]

Yes. They are open, quad port. Beside the point. I am asking... Most engines have larger primary than secondary, my 290 has smaller primary than secondary. WHY? Any reason to LEAVE the design alone OR port the primary out like most other saws?
Sorry if I stutter. I'm a small engine mechanic with outboard training, tried hard to make my question as clear as possible. All apologies if I wasn't clear.

US

 

[UltraSwine]

I have run both jugs in various configs. I am not asking arbitrarily. The 290 has noticeably smaller primary than secondary transfers. I want to know if that matters.
Thanks for your reply.

US

 

[UltraSwine]

I have cut the base, set squish, cut the bearing and seal seats accordingly. Like others have done with Poulans and Macs. All I am asking is - should I port the primary transfers larger than the secondary transfers like even the 390 or just make my numbers right and profit from tighter primaries of the 290? Having dropped the jug 0.040-0.050 I certainly have to raise the transfers (shamelessly ripping off Alpina design) I only ask if I should open the smaller-than-secondary transfers. Like the 390? Like the 200T? Or... should I work with/around tighter primaries?
Thanks.

US

 

[UltraSwine]

No worries. I'll figure it out. Thanks. Also in process of adapting HD filter to the 290. So far, nobody's "input" has been useful with that, either. SSDD.
Be cool, don't take any wooden nickels.

US

 

[huskihl]

From what I have seen, many primaries are the same size as secondaries, some are bigger, and some smaller. I don’t know why they did what they did or what their line of thinking was. If the primaries are bigger than the secondaries I open the primaries first. If the secondaries are bigger, I open them all at the same time

 

[Ketchup]

Post up a picture looking down into the transfers.
I’m guessing there isn’t a lot of distance between the primary and the exhaust. And it’s an open port. Easier to short circuit.
My bet is the designer was trying to keep fresh charge away from the exhaust port. Stihl has to meet emissions requirements. We care less about that as long as there’s a good scavenge loop.

 

[David Young]

Do they open at the same time? Do the primaries lead? If so it would tend to give more velocity in one direction.

Another guess would be an adaptation based on the bore stroke geometry. there is less bore to fill but percentage wise it is a taller column, secondaries being larger and angled differently could help to sweep the combustion chamber.