390 vs 372

parrisw

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Finally got around to running my 390. This is just the first run, on a brand new top end, so still a little tight yet. I think there is more in it, it was ported conservative for the first time in a 390. For those that haven't seen the vids on AS.

Same bar and chain, swapped between the two. 390 wearing a 8pin, 372 has 7pin.

[video=youtube;pb96p_Xoajk]http://www.youtube.com/watch?v=pb96p_Xoajk[/video]

[video=youtube;Vpkd-Xh30tU]http://www.youtube.com/watch?v=Vpkd-Xh30tU[/video]
 
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parrisw

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Will the 390 just dosnt sound like its running as free as the 372 are the #'s between the two dramatically differnt?
You may wanta work on the 372 carb sounds like the needle maybe leaking a bit ...
I have done 2 390's and I think both owners will tell ya the 372s wont get a smell...
Ya I hear ya, I thought the same thing. I said over at AS that the 390 doesn't impress me like the 372 does. The 390 timing is unchanged except for what the machine work had altered it, I think the ex was at 165°dur. The 390 has higher ex, I think that 372 is only 162° dur on ex, 160°dur intake, and maybe 120 atdc on the transfers. The 372 had much more transfer work then the 390, I didn't really touch the 390 transfers much at all, I widened the uppers a little that was it, and slightly opened the lowers, I was figureing I was going to have to go into the 390 again, just wanted to take it easy since its my first time in one.

The 372 is more broke in then the 390 as well. The 372 is set about 1000rpm higher as well.

How can ya tell by the sound of the 372 that it needs carb work?
 
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parrisw

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The 372 sounded really loaded up when you picked it up to run it.
That's normally a sign its leaking a tad...
OH, ok, It's done that only when cold, I had just started it about 30s prior to starting the video. Although, its been worse the last two times. I'll give the carby a check over.

Any tips on the 390? I was planning on putting a few tanks through it then going from there. I've just heard they like much different porting then 372's, so I'm going slow till I figure them out. Sorry I accidentally deleted all the PM's we shared on AS about the 390's.
 

parrisw

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Well will I suppose thats depends on what kind of porting you put in your 372's....
I brought the ext port down to 98* left the intake and raised the transfer to 120*
Ok, thanks. Sorry I'm bad at remembering #s on the saws I've done. Its all documented over on AS in my build threads though. That 372 is the best one I've done so far, and getting ready to do another.
 
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parrisw

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Hey Eric I went back and looked what the 390 numbers were at.

EX 97.5atdc 165dur

Intake closes 76.5ftdc 153dur

Transfers 121atdc

Blowdown 23.5


I was thinking that the transfers can come up 3° to start. With lowering the cylinder, I did loose some transfer time/area, and I only widened them a little, so I did loose some transfer. Going to run it for a few tanks then take it back apart. I also think it needs more intake, I may lower the cylinder more to get more compression too.
 

blsnelling

Slower than stock porting specialist
Jan 10, 2012
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Hey Eric I went back and looked what the 390 numbers were at.

EX 97.5atdc 165dur

Intake closes 76.5ftdc 153dur

Transfers 121atdc

Blowdown 23.5


I was thinking that the transfers can come up 3° to start. With lowering the cylinder, I did loose some transfer time/area, and I only widened them a little, so I did loose some transfer. Going to run it for a few tanks then take it back apart. I also think it needs more intake, I may lower the cylinder more to get more compression too.
I would raise the transfers 3 and drop the intake 8. No, that isn't a typo:)
 
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blsnelling

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Jan 10, 2012
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[video=youtube_share;3vT4DeVoyd0]http://youtu.be/3vT4DeVoyd0[/video]
 

TK

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Not to distract but I gotta ask - What's with the fluttering in RPM's in some of the cuts? I hear that elsewhere as well sometimes, but it caught my attention in the 390 vid. Not so much the 372, definitely on the 390. Not everytime but some cuts it had that fluttery sound to it, rapid fluctuations in speed almost like a grabby chain or something but the saw doesn't appear to jerk around at all.
 

mweba

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Not to distract but I gotta ask - What's with the fluttering in RPM's in some of the cuts? I hear that elsewhere as well sometimes, but it caught my attention in the 390 vid. Not so much the 372, definitely on the 390. Not everytime but some cuts it had that fluttery sound to it, rapid fluctuations in speed almost like a grabby chain or something but the saw doesn't appear to jerk around at all.
That's the "sweet spot":thumbsup:
 
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parrisw

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Not to distract but I gotta ask - What's with the fluttering in RPM's in some of the cuts? I hear that elsewhere as well sometimes, but it caught my attention in the 390 vid. Not so much the 372, definitely on the 390. Not everytime but some cuts it had that fluttery sound to it, rapid fluctuations in speed almost like a grabby chain or something but the saw doesn't appear to jerk around at all.
Ya it's the chain.
 
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