Stihl Saw...Tillotson Carb Problem

[etbrown4]

This is a Stihl Concrete Saw, TS400.....it's the first cousin to a heavy Stihl Chain saw, so I though some posters might have some ideas! I'm guessing the same carbs might be used in lots of other saws. (I don;t have the carb # yet)

It is 3.9ci, and has a 1.93" bore and a 1.34" stroke, and it makes a lot of power when it runs!

I'm sure it's dried corn in the fuel. I've thoroughly cleaned this carb, but it still won't start except on starting fluid for a few seconds. (yes, please don;t tell me about starting fluid, because I know )

I've cleaned many dozens of 2 cycle carbs including pulling the needle valves.

The only thing I'm unsure of on this one is there is a flat brass round fitting under one of the 4 screw end covers. The flat brass is round like a circle, maybe 3/8" diameter, and it has a hole in the center.

I've liberally sprayed carb cleaner there, and can't tell if it's getting through or not. I don;t have a wire that small for probing, as it's a real small opening.

Anybody seen this flat brass fitting ins a Tillotson carb on any Stihl unit, and if so, have ideas of how to check it

Other ideas?

 

[SEAM]

Did you check the impulse line (between crankcase and carb) ??

 

[etbrown4]

All the rubber lines seem to be in good shape and secure. Not sure exactly, but guess that the impulse line is a rubber line, carrying vacuum from the crankcase.

Either way, It's definitely a fuel problem, and it's is clearly not picking up the fuel.

Prior to cleaning there was a little solid corn visible in the carb, so it's likely there's a tiny bit still in there, that I can see or get with spray.

Curious if anyone knows how to clean or test that flat top, round brass fitting with the very small hole in it? Or if it's particularly important?

Just guessing it may be found on many tillotson carbs. ???

 

[jackjcc]

Generally that piece with the hole does not have a hole in it. While I don't yet understand the purpose in the piece, i do know that rebuild kits have one so it must be a part that needs replacing. Anybody explain the purpose of that round little dome next to the needle valve?

 

[etbrown4]

This is not a dome. It's smooth and flat, and about 3/8" diameter with a really tiny hole.

 

[SEAM]

The impulse line drives the pump diaphragm in the carb - if it is not airtight (or connected), there will be no fuel drawn from the tank.