I recently picked up a Stihl 066 Magnum, and I am currently chasing an idle issue.  Compression on the saw is very good at 150 PSI, but I have not been able to get the saw to idle.  It will rev through the RPMs quite well, but simply will not stay idled and will quickly shut off without feathering the throttle.

I went ahead and pulled/cleaned the carb, including pulling the H & L jets and cleaning their passages as well.  I started with both jets 1 turn out from stop, and have been able to now get the saw to idle fairly well around 2800 RPM with a handheld tach.  Problem is, now it has sluggish acceleration, an intermittent idle surge to 4k+, and will intermittently be very slow to idle back down once the throttle is released from max throttle.  I can adjust the L jet to get the throttle response issues and surging idle corrected, but it runs right back into the saw not wanting to idle.  I've confirmed that the idle screw is making positive contact with the throttle arm on the carb.

After talking with some of the guys on Arboristsite, its been suggested that the fuel metering lever in the Walbro carb is out of adjustment.  Looks like this is an easy fix, but without the Walbro tool, I am not sure of the specs.  Most of my online research suggests .065" below body of the carb, but I am not sure if this is a set number for all Walbro carbs, or just certain models.

Anyone ever adjusted the fuel metering lever with good results?  Or, does it sound like my issue may be elsewhere?  Thanks!

Did you replace the diaphragm in the carb or just clean the carb?

New gasket when you replaced carb? Carb on tight? I had that happen w/my 044 after I rebuilt the carb.

Diaphragm looked fine, not tears or holes, still remained flexible and pliable.  Now, I will likely go ahead and get a carb rebuild kit, as there really is no reason not to rebuild at this point.  



Carb is on tight, and like the diaphragm, gasket looked good.  No brittle spots, and no obvious damage.

Walbro and Zama rebuild kits are under $10, just do it.

I thought one of my Zama's was fine after looking it over externally.   The intake screen was plugged with whitish crap, and the diaphram didn't have the elasticity of the newer one (probably due to the ethanol).  

Just rebuild it and adjust the H and L and idle per online tutorials.

clean out the muffler, it's clogged up from running to much oil

Nope, muffler is clean....it was one of the first things I removed when I cleaned up the saw.  Plus, I wanted to get a good look at the piston, which was nice and shiny.  

my Stihl saw wasn't running, got part number off carb, bought a new Zama carb on Ebay, installed, easy

I was this close ---> <--- to replacing the carb on a Stihl FS45 last year.  It is the smoothest running trimmer I have ever owned, but was the biggest PITA to crank....at least, until I figured out the proper way to crank the damned thing.

As far as replacing the carb, it certainly would be cheaper to go with an aftermarket replacement.  That being said, I'm not quite ready to admit defeat with the Walbro yet...

Walbro carbs are cheap....ditch and replace

Surging idle and hesitation sounds lean to me. Check for a vacuum leak after the carb.

Have you replaced the fuel line yet?
If so, have the thing vaccum tested for crank seal leaks.

If not, replace the fuel line, and impulse line before taking another step.

This is next on my list...

Good!!!

I dunno how many times in recent years I have gone on a hairy assed crusade, only ti figure out the dadgum lines were cracked.
They are cheap and easy to swap. Odds are they need to be updated to the newer corn resistant lines anyhow.

An easy way to tell if you have a crank seal issue, is running the saw on one side, then the other and paying attention to how it runs.
It's not 100%, but a seal with a slight leak will become obvious, most times.

Keep an eye on the spark plug, and any signs of running lean while you are tinkering.

AS is a great resource. So is Sawhawgz.
AS lost a LOT of their talent base a while back, and most defected to the Hawgz site after a HUGE blowout.
Hawgz is a LOT like GD at times though..it's not for the meek.

Although I know it isn't the perfect method for checking fuel lines, a lot can be gathered simply by how easy they are to remove from the inlet barb.  Just about every small engine I've encountered with fuel line issues required the fuel line to be cut from the barb.  Most are dry rotted and brittle, and some have practically fused themselves to the barb.  This one, surprisingly enough, pulled off fairly easily.  That being said, there's really no reason not to replace the lines.  



I tried this when I first started tinkering with the saw, and really found no discernible difference flipping the saw from side to side.    



I've pulled the plug a couple times while troubleshooting the saw, and its looked fine each time.  Coloration is perfect from all the manuals I have, and it hasn't been wet or oiled over, and heat range looks correct.  I believe there may be a pic of the plug in the thread below:

https://www.americanresearchltd.org/core/topic.html?b=1&f=5&t=1670475



Just to be curious, what was the big blowout all about?

The Blowout was coming for a long time, and it went down the crapper like most mismanaged forums do.

LOTS of fragile little West coast liberal egos, and a couple precious darlings of the Libtard stripe, managed to abuse their position as moderators for too long, got people pissed.

The owner went hands off for a while, and a couple west coast liberal mods and their supporters, started banning long time members(Huge contributors of content) as well as a couple paying sponsors, for petty reasons.

The fur was flying, and people were already leaving, when a NASTY Virus hit the servers, and from there it was a comedy of errors, as well as outright hostility, towards some who had started posting on the Hawgz site. It even ended up on facebook with the owner getting nasty with upset members there.

 The Owner tried to band aid his servers, and take the cheap route, and the attacks continued, until the owner had to invest in a complete change over, resulting in a HUGE loss of contributed information on historic saws, important repair hacks, Climbing and Arborist info, and logging history. Some stuff was saved, but a LOT was lost for good, and some of it was very important to the collectors as a resource.

The loss as a resource was just too much for some. Quite a bit that was lost, was posted by guys who are now gone, and they lived the logging heydays.

The rest of us that like to bust each others chops, and call a spade by it's name, pretty much just GTFO before getting permabanned, or went out in a blaze.

The guys that are still there, are mostly new guys and a few retreads, with a few that still go between, including one looney mod(NFA Junkie) that is the last remaining bit of sanity.
(Names have been omitted, details left out for brevity and decency)

The place just isn't the same without the people it once had..