Tillotson HD

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Tillotson HD

Postby panhead_kicker » Mon Sep 05, 2022 11:26 am

Hello all,
New to the forum. Hoping to learn what I can about the Tillotson HD series carbs here. I am a bigtwin owner. The technical section and service bulletins are great. I've studied the HD fuel flow and cross section diagrams such as in SB 518, and have a question I hope someone can answer. As I clean a stripped body of an HD2D with carb spray, I noticed a small opening in the bore I had not seen before. At first I thought it to be a casting flaw, but then found the same opening in multiple bodies. Looking into the bore from the choke end, the opening is in the floor of the bore, to the right of the small boost venturi. The cross section diagram does not indicate an opening here.
The only answer I can come up with is that the cross section diagram is wrong in identifying the location of the "Idle Air Bleed" channel.
Has anyone else noticed this?
panhead_kicker
 
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Re: Tillotson HD

Postby wz507 » Mon Sep 05, 2022 2:29 pm

Could you post an image of the referenced hole? When looking over the carb body, if you can't find any other source for atmospheric idle air, you may very likely be correct. If you have a needle and syringe you could inject solvent in the subject hole and by observing the solvent flow determine which circuit this orifice/galley is part of.

Do you have this Tillotson manual?
Tillotson HD Manual.jpg
Tillotson HD Manual.jpg (229.7 KiB) Viewed 644 times

The image below is from the Tillotson HD manual and suggests that idle air enters the circuit just downstream of the venturi at labeled position #3. Do you see this orifice on your carb?
Tillotson HD Idle Air.jpg
Tillotson HD Idle Air.jpg (219.68 KiB) Viewed 644 times
wz507
 
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Re: Tillotson HD

Postby panhead_kicker » Mon Sep 05, 2022 4:48 pm

Hey thanks for the reply!
Pretty difficult to get good pic with only a phone, but here is the location, dark spot at end of arrow. It ties into a diagonal drill shaft straight from diaphragm rim area, and also connects to the intermediate jet area. I only noticed it by spraying carb cleaner with the straw into the diagonal shaft, causing fluid to jet from the hole. I think I have looked at all the literature on the site, both Harley and Tillotson. I prefer the Harley service bulletin 518 drawing, as it is more depictive of the HD2D than the Tillotson diagram.

A72D6C8E-144D-43CF-85B8-CC901257FC09.jpeg
A72D6C8E-144D-43CF-85B8-CC901257FC09.jpeg (65.44 KiB) Viewed 620 times
panhead_kicker
 
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Re: Tillotson HD

Postby panhead_kicker » Mon Sep 05, 2022 7:28 pm

wz507 wrote:
The image below is from the Tillotson HD manual and suggests that idle air enters the circuit just downstream of the venturi at labeled position #3. Do you see this orifice on your carb?
Tillotson HD Idle Air.jpg

And to answer your question directly, in my carb there is no orifice downstream of the venturi except for the idle discharge ports which lie at the top of the bore for this model.
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