Tillotson HS-273 Carb - Anyone know about this brand of carb and it's inner workings?

[etbrown4]

I have this carb in a saw and the saw runs great but will not idle.

If you hold the slightest pressure on the trigger it will run smoothly at low rpm, but when you let off the trigger, it stops.

I don't see an idle stop on the carb and I don't see one as part of the saw either.

There is an idle adjustment screw in the carb body, though it's not part of the external throttle linkage. Adjusting that internal adjuster has no effect, so far.

Here is a link to Tillotson's breakdown sketch http://www.tillotson.ie/docs/HSPartsList.pdf

It's on a 3 brands of 2 cycle saws, though my question is more of a carb question than a saw question if anyone can help.:msp_unsure:


PS. Here's the Tillotson service manual describing their troubleshooting tips etc. http://www.tillotson.ie/docs/techinfo_HS_US.pdf
And no, I've not tried all their tips yet!:smile2:

 

[turtle561]

2 of the three spare hs i have use an adj. screw on the carb body, #20 in the drawing. the other hs has an angled tab on the throttle shaft that a screw from the saw body acts on. could be a screw is missing ?
# 28 is a governor valve that can be blocked off if necessary.
what saw is this ?

 

[cambl]

The HS is a very simple carb and easy to rebuild. Sounds like your idle speed screw is missing.

 

[mactodd]

This wouldn't be on a Poulan 306 or 245, would it?

 

[etbrown4]

It's on a Dolmar Saw.

How about this question:

Have any of you seen saws, esp. those using a Tillotson carb, where there is no external mechanical throttle stop, or idle stop?

This carb has an internal adjustment screw which is supposed to control the idle speed internally, but mine is not working.

I was thinking that if all saws pretty much have external mechanical idle stops in the linkage, them maybe I just haven't found mine, or a screw has dropped off etc.

On the other hand, if it is common for saws not to have an external, mechanical idle or throttle stop, then I have no where to go but to go inside the carb!

Curious what others have seen.