stihl 084 running out lean at WOT?

[Hydro74]

Howdy
Ive got two saws that I have recently rebuilt, and both have the same issues. I have a stihl 084 and a stihl 038 magnum, both have had the seals replaced with oem ones, new oem fuel lines and filters, new plugs and both have been pressure and vacuum tested with no leaks, carbs have also been rebuilt and tested. The problem I am having is both saws at wide open throttle rev way to high even with the h jet back out they both still run away. They both idle fine and both start easily with good compression (new rings in both) Im at a stand still with both of these i've re built a few of each of these both before and never had this issue, any thoughts?

 

[Hdtoolmkr765]

Have you checked impulse hoses and intakes? You have a leak somewhere.

 

[Sam R]

My thinking also goes to an air leak somewhere. Or, could a leaking H circuit in the carb cause runaway revving at wide throttle angles?

 

[Wood Doctor]

Looks like you did everything but replace the carburetor. The Tillotson Hi setscrew on the 084 can no longer reduce the air-fuel ratio as you open it up. So, you are running too lean. I suggest you rebuild or replace the carb.

 

[Chainsaw Jim]

It's probably slow breathing grub screws if they're still in the tank vent tubing. Replace them with a better vent like one of those white echo ones.

 

[Hydro74]

UPDATE:
So I figured out the 084 issue and as I’m embarrassed to say....the impulse line had come off from the tank body doh! I can’t believe it actually started and ran! Put her back on and bingo problem solved. The 038mag however is a different story I’ll keep dissecting it until I find out the culprit thanks all your replies guys and keep them coming!

 

[Sam R]

UPDATE:
So I figured out the 084 issue and as I’m embarrassed to say....the impulse line had come off from the tank body doh! I can’t believe it actually started and ran! Put her back on a bingo problem solved. The 038mag however is a different story I’ll keep dissecting it until I find out the culprit thanks all your replies guys and keep me coming!

HA! I got to admit I've done that too on the trimmers that have the fat impulse hose I've managed to get those carbs plugged in and not hooked to the impulse.

 

[Wood Doctor]

UPDATE:
So I figured out the 084 issue and as I’m embarrassed to say....the impulse line had come off from the tank body doh! I can’t believe it actually started and ran! Put her back on and bingo problem solved. The 038mag however is a different story I’ll keep dissecting it until I find out the culprit thanks all your replies guys and keep them coming!

That is surprising. Usually a loose, cracked, or missing impulse hose produces other symptoms, such as erratic running. That's what I ran into with an 038 that I wish I still owned. Hang onto that 084. Demand for them is still very good after 25 years.

 

[Sam R]

That is surprising. Usually a loose, cracked, or missing impulse hose produces other symptoms, such as erratic running. That's what I ran into with an 038 that I wish I still owned. Hang onto that 084. Demand for them is still very good after 25 years.

I agree it would, but then again it is also another way for air to get in causing that lean revving... Strange that it would run very well at all with no fuel pump, though. That's just Stihl engineering being so awesome!