Thread: husky 3120xp for bobl

Hi ya Bobl,

I have to agree on the saw being more "fumey" to work...but after raosting a barrle/piston...on 40;1...and not finding any blockage in the carb...I'd then have to question whether there's been a manufacturing glitch with mine and my mates saw...can't say I've ever liked the idea of no main jet screw...the saw's been OK previously in bucking...but on its side milling...has always sounded a little strained at the top end...and it only took one slabbing cut...on this particular day...and she was fried.

There was a noticable clean ring near the center of the piston that indicated pre-ignition and a lean mix.

Originally Posted by errolc

I've since made a minor enlargement to the main jet with really good results...

Hi Errol,

how much did you enlarge the jet size, did you drill it out?

Originally Posted by Ironwood

Hi Errol,

how much did you enlarge the jet size, did you drill it out?

Just increasing the jet size alone won't necessarily improve the cutting performance on a saw like a 3120. They already have a lot of power so even more power makes little or no difference in smaller to medium size logs. High power saws are not limited by power but the ability of a chain to cut and remove sawdust - this is a chain and chain speed issue and not a power issue. Extra power can produce increased chain speed by increasing the sprocket sizem but going from a 7 to an 8 tooth sprocket requires at least 14% more power to justify this and it drops the operational torque so it doesn't work so well on big logs.

The newer 3120 models are rev limited by the coil to 9600 rpm, so just increasing the jet won't give any more chain speed, the engine will just hit the rev limiter quicker than it otherwise would and just run richer. In Errol's case it sounds like his was running too lean to begin with and he is using it to protect his saw from seizing again but you should not need to do this with a new saw as they should run and mill just fine as stock saws (I have done this with a 3120). Adding a bigger jet will use more fuel and maybe help the saw run cooler but I don't think it will cut much more wood unless perhaps you are milling really big logs.

The 3120 is a good saw but its weakest link is it's relatively low chain speed.
To increasing the chain speed
- the coil has to be swapped out for a non-limiting one,
- then the exhaust can be opened up allowing the saw to breather easier.
- then adding bigger jet then becomes essential otherwise the saw runs too lean. Ideally the whole carby should be replaced with an adjustable one because fixed jets means you cannot really tune a modified saw properly and get it right on song.
- finally the saw benefits from some mild porting.
You can read about different jets changing the coil and other ways of souping up a 3120 ad nauseum on the aboristsite. eg "www.arboristsite.com/showthread.php?t=88134" shows how to get 12k rpm out of a stock 3120. Together these mods generate more power and chain speed than just changing the jet.

By the time this is all done it might have been more financially wise to fork up the extra for an 880, coil limited to 12k rpm and the carby is adjustable (up to a point), then its a matter of just opening up the exhaust (up to a point) and adjusting the carby.

Originally Posted by BobL

Just increasing the jet size alone won't necessarily improve the cutting performance on a saw like a 3120........................... ................................................................Ideally the whole carby should be replaced with an adjustable one because fixed jets means you cannot really tune a modified saw properly and get it right on song.

Hi Bob,

I wasnt after more power from my saw, if you re-read my previous post ( #8 ). What I was trying to achieve about 6 years ago, was to prevent my saw from running lean, if I fitted a large remote airfilter to it.
I am not interested in doing this mod now, as I very rarely have time to do any milling, as I work 7 days a week running my business.
I was interested to know how Errol went about it on his saw though, just out of interests sake.
Thanks for posting the link to the arborist site, I will have a look when time permits.

Originally Posted by Ironwood

Hi Bob,

I wasnt after more power from my saw, if you re-read my previous post ( #8 ). What I was trying to achieve about 6 years ago, was to prevent my saw from running lean, if I fitted a large remote airfilter to it.

There was a lengthy discussion about using oversize air filters on big saws and if that would make the saws run lean on the abroristsite not that long ago. The consensus from the experts was that provided a saw is tuned with a properly cleaned filter it will not run lean even if an air leak develops before the carby, or the filter is removed, or oversized filters added. Saws are designed so that when the air filter is clean it is not the limiting step in the air intake pathway. What primarily determines the maximum amount of air taken into a cylinder is the cross sectional area of the carby throat and transfer ports. A saw tuned with a clean filter starts out with the correct richness, and as the air filter clogs, the saw just heads into the rich side of tuning, which won't harm it, well not like making it too lean. What is important here is not to tune the saw with a clogged air filter because then if you remove or clean the filter it can then run lean.

I agree it's not intuitive and you have to get your head around it, but if you think about the way that it has been done it makes sense. This is also not to be confused with air leaks that happen in or after the carby, which can lead to very serious leaness problems.

I am not interested in doing this mod now, as I very rarely have time to do any milling, as I work 7 days a week running my business.
I was interested to know how Errol went about it on his saw though, just out of interests sake.
Thanks for posting the link to the arborist site, I will have a look when time permits.

No worries.