Compression numbers.

[FourMoCajuns]

My 6401 has 130# compression and Floods very easy. Can these be related?

 

[Lakeside53]

Yes. Low compression (130 IS very low) makes it hard to start and more prone to flooding... I see saws every day just like that. New rings, or piston etc, and they snap to life.

 

[DGG]

I have a dumb question. What is the compression on a brand new broken in saw? Any difference in compression between different models? I have never had a reason to check mine.

 

[robby26wi]

every saw is different...seems like the smaller saws actually have higher compression....My 5100 has 175 and my 7900 has 155 as does my 288...Most of the larger saws i have owned seemed to be a touch less then there smaller counter parts...as for a range i would say that anything over 140 is pretty good...140-180 is the norm....anything over that and you could have some detonation issues and anything lower causes for hard starting and less power...If its 130 cold thats like 100 or less hot...

 

[cuttinscott]

130 lbs is fine, I Just took a reading of a branny new PS6400 and got 130 lbs as well. If the saw is flooding take a peek at the carb.

Scott

 

[robby26wi]

wow 130 seems low for a new saw...My 7900 has like 5 tanks through it and it has 155 and i am sure that will go higher....But i guess if the 6400 is dry that would make a difference...

 

[cuttinscott]

That was a reading off a new saw and yes the rings are not seated yet. But 130lbs. is fine.

Scott

 

[Lakeside53]

130 lbs is fine, I Just took a reading of a branny new PS6400 and got 130 lbs as well. If the saw is flooding take a peek at the carb.

Scott

If it's been used, 130 is pretty bad... I return most of those to the customer with a quote for repair and a min charge... However.. brand new isn't a good measure - try it after two tanks or more. How's your gauge?

Stihl's tend to have 150+ to 160 out of the box. Often rising to 170 or so soon thereafter. Spike60 (I think) tells me that some Husky's are quite low out of the box, but rise quicky in use. Don't know about Dolmars.

 

[cuttinscott]

Anything over 120 lbs. is acceptable for Dolmars as far as my gauge its a Snap On EEPV303B small engine / motorcycle style, the same gauge that reads 175 - 190 on the PS5100's. Also I just checked a Well Used up Logger Saw PS6400 with thousands of hours and it will still run at 105 lbs. but she is tired and rattles. It is a shame that a Stihl will not run at less than 125 lbs :hmm3grin2orange:

Scott

 

[Lakeside53]

They'll run at 125, but like low power pigs... and be prone to flooding. At 120, I don't call it "acceptable"... more like "just about dead". I wouldn't own one like that. Obviously more of an issue with smaller displacement saws, but..

What should a 6401 read at mid-life? Surely it's 150 or so...? and therefore at 120 it will also be way way down on power

 

[FourMoCajuns]

Dumb question. What is the compression on a brand new saw? Any difference in compression between different models? I have never had a reason to check mine.

WTF do ya mean dumb question?

 

[Peacock]

WTF do ya mean dumb question?

He was referring to his question. I'm sure he wasn't talking about your very not dumb question.

 

[timberwolf]

It does depend where the compression is lost, blow by into the exhaust port from some exhaust side scoring does not hurt the saw as much as blow by going down the back side of the piston into the intake or transfers.

In that respect a saw with scoring on the exhaust port side might run ok with lower compression than a saw with intake side damage or wear.

 

[FourMoCajuns]

OK my bad.

 

[sugarbush]

6401- 6400 will read about 160# new, before running. I don't think anything under 135# is good in any brand. you start to get idleing and starting problems.

 

[Dan Forsh]

Amazing, this is one area where I thought opinions would be pretty unanimous

 

[Lakeside53]

Then we'd all be bored and go home..

 

[Peacock]

You just need to check compression on each cylinder and compare. Is it using coolant? Use a borescope and check the exhaust valve for deposits. Did you check for leak down with the piston at BDC?

 

[Lakeside53]

huh? It's one cylinder two smoker...

 

[FourMoCajuns]

You just need to check compression on each cylinder and compare. Is it using coolant? Use a borescope and check the exhaust valve for deposits. Did you check for leak down with the piston at BDC?

:jawdrop: :crazy1: