my 372 keeps leaning out? why?

[superloggy]

hello can anyone tell me how I can get my 372 to run consistently. I'm a log home builder and always on and off the gas. Even after setting max rpms saw wants to lean surge at part throttle even though low end jet is set fine. I think its the epa jetting limiters things? Oh ya I forgot to mention Its piped walker style. I love the saw it has awesome power I just don't want it to calf. Any adice would be apreciated.

 

[Lawn Masters]

You're saying you've had the muffler modifed right? if thats whats been done, and the carb hasnt been adjusted to a richer setting yet then you need to have that done.
I havent heard of limiter caps on the 372's carburetor adjusting screws, but then again, I've never worked on a 372 before either, but I do know that you have to get the settings richer on your carb, if you dont know how to do that then I would advise you to be very careful and document how far you've turned the screws, which way they were turned and which screws were turned.

I start by turning the screws 1/10th of a turn at a time, and then if you know what to do and listen for, the saw SHOULD run like a new perfectly tuned saw does.
Good luck with the tuning work. Oh yeah for limiter caps on adjuting screws, I've pulled them off with a pair of needle nose pliers without too much trouble from them about coming off, just be careful to only grab the plastic cap and not the screw itself.

I claim no responsibility for any damage that may occur as a result of taking my advice and adjusting the carb.

 

[glens]

Hi superloggy; welcome to ArboristSite.  I want to offer my apologies for the previous post.  The young fellow's rather anxious.

Your carburetor may or may not have a part-load fixed jet which may or may not be replaceable (with the same or different size orifice).

Your simple choices are two:<ul><li>reinstall the stock muffler for which the part-load carburetion (if existent) is tuned<li>use the saw at only the two throttle positions for which you can tune</ul>Your complicated choice is to attempt modification of the part-load fixed jet (if it exists).

I don't know what carb is on that saw and don't have a Husky shop manual, but my Stihl carburetor document dated 2000 lists all their current (EPA) saws of the time as having part-load non-adjustable non-replaceable fixed jetting.&nbsp; That declaration notwithstanding, I only use my saws at full throttle where they only really work well.&nbsp; I'd assume your carb <i>does</i> have some sort of part-load jetting consideration, but ultimately my advice is to use the throttle like an on/off switch, timing the blips as necessary.

Good luck.&nbsp; I don't expect it, but maybe someone will come along with something you'd rather hear.

Glen

 

[Sethro]

MR. Super
A couple things to check,is the fuel filter the same color as your mix? I am just a wood hick. but check your inake boot also(part thorttle)if surge takes most place a dirty carb. Wrong air is what will toast a bun. So 4 stroke it. Seth

 

[Kneejerk Bombas]

Sounds to me like an air leak. First thing I'd look at is intake boot.

 

[Marky Mark]

I just read your bio, if you are a wanna be chainsaw racer take it you guy who builds your race saws.

 

[Stumper]

Brian, The partial throttle jetting actually exists-it goes back to old Homelites in the '60s (maybe earlier). It is an internal jet inside the carb body-unlike the low and high jets we are all used to. You are correct that chainsaws are designed to be run at full throttle. I've been known to back off when finessing a cut but much partial throttle operation not only makes the saws run lousy it risks clutch damage.

 

[ricksvar]

From the information you've given it's the "partial throddle" comment that I feel may be the cause of the problem.Run your saw at full throddle.If the problem persist you have something to be concerned about,air leak etc.

I have a 20" bar on my 372 and never run it at partial throddle.The saw is seldom used without the bar under full load.If you're making a lot of cuts in small diameter wood(say 14" or less)a smaller saw would probably be more practical,or at full throddle just pull into the cut a little more with the 372.

Rick

 

[JimL]

sounds to me like its sucking air.

 

[Crofter]

Superloggy

You say you have trouble getting the 372 to run consistently. Does that mean sometimes it is ok and others not? Does it just mean it can be adjusted ok for low speed or high speed but is lean mid range. If the former it could be an air leak at boot, fuel, or pulse line that is affected by temperature or movement due to av mount travel. The limiters are only a problem if you cannot get proper mixture within that range. Sometimes a richer mid range mixture can be accomplished by slightly leaning high speed and richening low speed to compensate. Make SURE the High speed is still rich enough.

Frank

 

[glens]

Originally posted by RockyJSquirrel
To my knowledge, there is no such thing as a 'part-load fixed jet' on chainsaw carbs. Chainsaws have two jets, a main jet for full throttle and a low speed jet for idle. If you attempt to run a chainsaw for extended periods at part throttle, it will run lean- period. Chainsaws are not designed to run at part throttle. I'd say this one is operator error.

Brian,

Experience shows me that everything you said is true, as well comments on some technical pages such as http://www.aerocorsair.com/id27.htm (where the "no part-throttle operation of the Walbro" information seems to have been removed, or maybe I just missed it).

Having come into possession of some documentation has caused me to wonder a little bit about the veracity of your (and my previous) claims.&nbsp; Like I suggested, my saws don't seem to work any better at part throttle now that I have this information, but I can no longer take quite the firm stance I used to take because of it.&nbsp; The low and high speed jets are adjustable, but that doesn't mean there aren't other-speed jets.

One other thing I've learned by the documentation is that the newer carbs' low-speed jet gets its supply <i>after</i> (through) the high-speed jet, so changes made to the low-speed jet do not affect overall fuel quantity (at high speed operation) like happened when the circuits were independent.

Log home builders often do chainsaw carving-like trim work and I'm confident we'll find that's what "superloggy" is doing at part throttle (where the otherwise healthy saw just doesn't want to run [anymore, with the new muffler?]).

Glen

p.s.&nbsp; The 084 and 088 also have the part-load jetting, and the footnote "1)" in the listing indicates "CARB, EPA"

attachment is 73KB PDF file composed of select pages from the original; search it for the character string "part"

 

[jokers]

Glen,

I don`t have the time to review the documents you just posted, I`m on a short leash with a sick child(other child caretakers know what I mean), but in the previous part load fixed jets, they supplied about 10% fuel to the total. Enough to adequately fuel a saw locked on Hi idle.

Carvers and log home builders who sweep with their saws are notorious for cooking them.

Gotta run!

Russ

 

[Crofter]

Thanks for that info Glen

You dont happen to have any similar links for Zama do you. Experimenting back and forth between L and H seems to effect the mid range on my Zama 372 (365). I dont like to be caught talking thru my hat. With that fixed Mid Range jet, could there be dirt separately in there?

Frank

 

[glens]

Frank, both Zama and Walbro are represented within that document.&nbsp; The carburetor on my 036 is a Zama and that on my 066 a Walbro.

In my opinion the treatment on the last page I included is a bit lean.

I'll see if I can locate something more Husqv for you.

Glen

 

[superloggy]

thanks guys you all have some good ideas some more interesting than others. But you have given me alot of leads to persue. If I was just falling or bucking the saw would be fine but often as others suggested I'm just brushing with the tip or cutting a slot an inch or so deep while following a pencil line. The bar is rarely in the wood to an great extent so theres no load then lots of load I requires a certain degree of throttle control and carb doesnt like to transition well repeatedly. I know its not the saws intended purpose but have had saw that work fine and dont act like this . The older saws before epa stuff never did this . Other saws in the yard do this namely stihl ms460 and 372 are the worst though.
Thanks again for taking the time to read my gripes and offering advice. I can tell you all enjoy it as much as I do and if you have any log building questions I'd enjoying returning the favor.