Stihl 440 rebuild-carb ?

[Deere80]

Just like to say hello this is my first post on the forum, have read a lot on here and learned a lot also from you guys.  So last night I rebuilt my Stihl 440 with a NWP kit which I went with the big bore kit to get a little more power.  I was adjusting on the H & L screws to what I had found on the internet but some say to go more than a turn on the H screw but mine only will turn 1 revolution then stop.  I pulled the black rubber Sleeve that is in there so I can actually see how much I was turning the screws.  I am turning a red plastic insert,  do I need to tear that out to get down to the metal screw?  I am the first owner of this saw which I bought it I think in 2004 or 05 so anything done to this I would have done it.  It seems not to be getting to full RPM, how would I adjust that?  Also what screw is the one below the H&L screws?  I am guessing the idle but when I turn on it nothing seems to happen, it is idling to high because my chain never stops even when you are not touching the throttle.  Any help would be appreciated, thanks.

[dougand3]

Welcome. The plastic limiters can be removed for free tuning. You may need a special carb tool - eg: splined.
The H-L screws are together. L is always closest to the cylinder.  CW closes/leans fuel. CCW opens/richens fuel.
The Idle/LA/TAS is above or below the H-L set. CW speeds up. CCW slows down.
Search youtube "mweba How to tune a chainsaw".

If the carb is 12yo and had ethanol fuel in it, I'd consider a new one. AM clone is ~$15 or OEM shouldn't be too high.

[Deere80]

It has never had ethanol gas ran in it, what happened was I ran some old gas in it a couple years ago and scored the piston so I just pulled it apart cleaned the piston and cylinder up with emery cloth then put it back together since I was in the middle of cutting firewood for the winter to heat my shop and didn't want to wait.  It was working fine but was getting tired so I am just getting around to it now.  I will watch that youtube video and see if I can get it tuned better.  How much can a guy open up the exhaust hole in the muffler to get it to breath better with out screwing something up?

[thecfarm]

Deere80,welcome to the forum.

[dougand3]

On muffler opening, I'd try smaller increase first -  make exit hole ~ 25% bigger, then tune richer.
In tuning, if you can't get a stable smooth tune, it could be the carb is dirty or diaphragms or somewhat stiff. A rebuild kit runs $6-$12. When a new AM carb is $14, I go that route.  If main needle check valve is flaky, you need a new carb.

[Deere80]

Sounds good, I will get one of them carbs coming.  Where is the best place to buy one?  I am going to look at a used 026 tonight that looks to be in really nice shape so I have another saw because a couple months ago I bought a sawmill and put a 32in bar on the 440 to slim up the logs that will not fit on the mill.  Then I will have a smaller saw for the littler jobs and won't have to lug that heavier one around.

[dougand3]

Chainsawr is a sponsor here - you can check there. You can search ebay for Stihl 440 carb. The AM carbs all look similar - I go for best price and shipping time.

[joe_indi]

These images show how to remove those red limiter caps on the H and L screws with just a brass screw as the removal tool

[Deere80]

Thank you Joe, pictures are always the best.  Never thought of doing that, I will get to that project tomorrow morning.

[AdkStihl]

Big bore kits never make any more power than an OEM top end and in most cases actually generate LESS power due to the inconsistent port heights.
And now that STIHL (& Husqvarna) has lowered the price on most of their top end kits, its not even justifiable to buy an aftermarket top.

Example: Meteor top end kit for a Husqvarna 55 = $129.99  /  OEM = $107.45 out the door.