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TR2/3/3A Wrong carbs on my TR3

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Royal_58

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Well it seems that I have the incorrect carbs on my car. I seem to have the "HD" type. Moss shows that it is froma a AH BJ8. Oh well no Concours d'Elegance for me!
 
I don't have a book on the SU carbs so I have a few questions for the experts.

Do all SU carbs tune the same way?

Can I follow the same procedures in the service instruction manual for the TR2/3?

What kind of oil is "dashpot oil" and can it be purchased at Napa or Auto Zone?

More to follow I'm sur as I get deeper into the process.
 
Royal_58 said:
Do all SU carbs tune the same way?
Click to expand...
Well, kinda. But the details vary significantly. My book shows that the HD8 uses a needle valve arrangement to set idle rpm instead of holding the main throttle plate open slightly (which must make synchronizing interesting); plus has a screw off to the side for adjusting mixture rather than a big nut like the stock H6 carbs do.<div class="ubbcode-block"><div class="ubbcode-header">Quote:] What kind of oil is "dashpot oil" and can it be purchased at Napa or Auto Zone? [/QUOTE]The type of oil is not critical at all; although the "weight" does make some difference. Since ordinary motor oil will work fine, yes, you can buy it at Napa or Auto Zone
grin.gif

I found that straight 20W worked best for me in my H6 carbs, but it definitely varies. Some folks even like ATF, but I find it gives me a "lean bog". Not really a stumble, but the engine doesn't take throttle quite as well as with heavier oil. The thicker the oil, the richer the mixture goes on acceleration.
 
Thanks Randall, interesting about the oil weight. I don't fully understand the SU's. What book are you using?
 
I agree about the 20 weight (3 in 1 oil is 20 weight btw). I've tried the atf and have had the same lean bog as the piston bodies raise too quickly. 30 weight is summer oil due to the heat in Az.
Check into the Austin Healey site for tune up hints.
 
The oil (combined with the damper) resists the upwards movement of the piston that forms the top of the venturi. So when you open the throttle wider and air flow increases, it takes some time for the piston to rise. While it's held down, the velocity of the air through the venturi increases, which increases the depression (slight vacuum) that pulls fuel through the jet; thereby making the mixture richer. The overall effect is similar to an accelerator pump on a fixed-venturi carb.

This is the book I pulled out to look up HD carbs
https://www.tower.com/haynes-weber-carburetor-manual-a-k-legg-paperback/wapi/101936612

Although the title says "Weber", it also contains information on SU and ZS carbs, including needle charts. Like most of the Haynes manuals IMO, it's not perfect but a whole lot better than nothing.

There is also some information available on-line in various places, including
https://www.jcna.com/library/tech/tech0006.html
 
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