Tillotson Carb

[Oletrapper]

I am hoping there is a Tillotson carb expert somewhere on the forum. I am working on a Homelite Super XL925 with a tillotson carb pictured below. The carburetor I'm working on is a HS 151. Pic below:

I have rebuilt the carb and there is an access hole (circled in red) to the carb throat with nothing there. See next pic.

That opening has a passage directly to the throat of the carb. Upper tiny hole in the throat, not the plate. (circled in blue) See next pic.


With the gasket mounted, nothing covers the hole circled in blue, previous in red? That is the inside surface facing the reed valves.There was nothing there when carburetor was removed. My question, should there be something there? Welsh plug? Or is it the way it should be? Any expert advice on this will be greatly appreciated. This carburetor is off of the Homelite Super XL 925 I posted in "What's on your bench" thread. Thanks, OT

 

[Mad Professor]

It is for air or fuel in the venturi. Is the "hole" the only point that connects to the venturi?

 

[Oletrapper]

It is for air or fuel in the venturi. Is the "hole" the only point that connects to the venturi?

It is the only external hole that connects to the venturi and would allow air to enter. Internal (under the welsh plug) there are three holes allowing fuel to enter. This hole, in my opinion, for air, is not being filtered in any manner that I can determine.
Edit: Although, it is inside the filter box at that point. The only contaminates that could get in there would be through the choke lever and throttle linkage passages.

 

[Oletrapper]

Well, I guess there are no experts on Tillotson carburetors. lol
My conclusion is that the passage way is there to assist with idle air. From a logical standpoint, it would have little significance air wise when the throttle is opened partially or fully. The only worry that still remains is why there is no screen there to prevent debris from entering.

 

[Bob Hedgecutter]

This should help you understand the internals.

https://tillotson.ie/wp-content/uploads/2015/07/techinfo_hs_us.pdf

 

[Oletrapper]

This should help you understand the internals.

https://tillotson.ie/wp-content/uploads/2015/07/techinfo_hs_us.pdf

Thanks Bob. Lots of studying to do. OT

 

[undee70ss]

That is for the governor, hs151’s have a governor to prevent xl925’s from overreacting.

 

[undee70ss]

Extra info

 

[Oletrapper]

That is for the governor, hs151’s have a governor to prevent xl925’s from overreacting.

Thanks Undee70ss. The carb does have a governor but I did not remove it. I can't find a substance to soften what they used to lock it in place. It's like bake-lite. Very brittle. Can you explain your meaning of overreacting? Just curious. OT

 

[Oletrapper]

Extra info

Before I rebuilt the carb, I turned L and H screws clockwise and counted turns until stop. L went in 1 1/2 turns and H went in 1/2 turn. After rebuild, I put them back to their previous settings. Pretty much as the instructions you sent indicated. The carb is still off the saw as I am in the process of cleaning it up. I won't know how the rebuild went until I get it all back together and try to start it. Thanks for your reply. OT