[TR] Dome oil

[Mark Hooper]

Hi Allen:

I'll have a go at that one.

Keeping the piston down as the butterfly valve is opened will increase the
vacuum in the carb body. Depending on the design, that could act to directly
suck more fuel up the passage around the needle, rather than depending on the
Venturi effect alone from the air rushing past the piston bottom. That assumes
there is no inbound limit on the air vent of the fuel bowl.

Of course, perhaps needle profile could use the Venturi effect alone, due to
some non-uniform fuel/air ration versus vacuum at specific piston heights.

There's my guess.

Cheers,

Mark Hooper
1972 TR6


-----Original Message-----
From: triumphs-bounces at autox.team.net [mailto:triumphs-bounces at autox.team.net]
On Behalf Of Allen Hess
Sent: March 21, 2012 11:41 AM
To: triumphs at autox.team.net
Subject: Re: [TR] Dome oil

On Mar 20, 2012, at 10:15 PM, triumphs-request at autox.team.net wrote:

> oil weight is quite literally the acceleration enrichment control.
> A thick oil will make it run richer by slowing the response of the
> piston, increasing air velocity over the bridge drawing more fuel
> a thinner oil will let the piston rise more rapidly, shortening the
> enrichment time.

I've no argument with the above but it always makes me ponder the
following. Since a rising piston/needle also allows more fuel to flow
due to a smaller needle diameter, I've always wondered about the
seeming contradiction in above. Can someone elaborate a little more?

Allen