Stihl 038 Super Carb Question

[TheTone]

I'm rebuilding a very early 038S with the old HK42 Tillotson carb. Disassembled and cleaned the carb and all components were remarkably fine. I don't know if this carb has been tinkered with, but there was evidence that Bubba and Junior had worked on the saw - the clutch cover washer was missing and I found it under the flywheel. When reassembled, the carb had a slow leak at 5 to 10 psi. It held 3 psi well, but I like my carbs to have rock solid pressure readings. I dunked it and bubbles came from within the venturi and none from the gaskets. I tried lengthening the metering spring slightly, but no change in the readings. The question is, does the end of the metering lever line up with the upper level (red arrow) or the lower level (blue arrow). I emailed Tillotson, but I'm impatient.

 

[HarleyT]

MMMMM.

 

[HarleyT]

A leak from around the venturi.....

 

[HarleyT]

Sounds like you are chasing some phantoms....

 

[HarleyT]

They may be "inner" demons......

 

[TheTone]

I examined the needle and seat with a dissecting microscope (from previous career) and they were like new. Not a hint of an annular ring on the needle tip. Figured it had to be something in the spring/lever/fulcrum complex. Can you tell me how to exorcise the "inner demons"?

 

[HarleyT]

It will take a vial of essential oils and a short oriental girl....

 

[HarleyT]

What is the reason for this post?

 

[HarleyT]

I have a feeling that you may be way off on your diagnosis....

 

[TheTone]

The reason for the post is to find the correct setting for the metering lever. If I'm way off on my diagnosis, please offer yours.

 

[HarleyT]

Why have you come to this question?

 

[pioneerguy600]

I'm rebuilding a very early 038S with the old HK42 Tillotson carb. Disassembled and cleaned the carb and all components were remarkably fine. I don't know if this carb has been tinkered with, but there was evidence that Bubba and Junior had worked on the saw - the clutch cover washer was missing and I found it under the flywheel. When reassembled, the carb had a slow leak at 5 to 10 psi. It held 3 psi well, but I like my carbs to have rock solid pressure readings. I dunked it and bubbles came from within the venturi and none from the gaskets. I tried lengthening the metering spring slightly, but no change in the readings. The question is, does the end of the metering lever line up with the upper level (red arrow) or the lower level (blue arrow). I emailed Tillotson, but I'm impatient.View attachment 659904

Flush with the red arrow area, commonly referred to as the fuel bowl.

 

[TheTone]

Thank you, pioneerguy600!

 

[a. palmer jr.]

I had trouble with the Tillotson on mine and replaced it with a Bing look alike and I'm glad I did...

 

[DND 9000]

From a Tillotson HK service manual (1984): The top of the inlet control lever should be flush with the diaphragm chamber floor (on your picture the area marked with the red arrow)

 

[TheTone]

Thanks for your response, DND9000. If you have a digital version of that manual that you would be willing to share, please send me a PM. I have other old Stihls with the HK series carb.

Edit: Nevermind, Tillotson just sent the HK manual. Thanks again.

 

[TheTone]

Follow-up: Dunked carb again, pressurized, and bubbles came from venturi. I removed the end cover over the metering lever and disassembled components. The needle valve and gaskets and diaphragm were soaked in AT-205 Re-Seal for an hour. In this old Tillotson the needle valve seat is incorporated in a plastic "metering module body". I cut a Q-Tip in half, dipped the tip of the stick end in water and then in baking soda and twirled the stick end on the valve seat to remove any unseen crud. After reassembly, the pressure test was much improved - it took 45 minutes for the pressure to go from 3 psi to 2. I'm calling it good to go.