I also have some interesting behaviour with my SU's. (I'm not sure of the
name - They are in my 72 MGB, and don't have the bowls on the side, but
underneath the carb.) When they are cold, and I let the choke off, the car
idles down nicely to 800 - 900 RPM. After driving around > 10 Mins, the idle
seems to pick up to 1100 RPM. Also, I can't get it to idle down any more than
that, as the idle adjust screws are backed all the way off. (I assume that I
am getting some extra air in somewhere.) Also, I'm set at about 10 - 15 BTDC.
Dave Hall
Greg Johnson wrote:
> On Thu, 2 May 1996, Allen W. wrote:
>
> > Have HIF4 Carbs on my 74-MGB. Has rebuilt engine with 8.8:1 pistons and
> > upgraded cam. Runs great all the time and idles great most of the time.
> > Can set idle @800 rpm and it will stay there for some random period of time.
> > Then it will drop to <500 rpm and nearly quit running. This usually occurs
> > after warmup. Floats and needles seem OK(carb rebuilt < a year ago). Can't
> > find any vacuum leaks. I need some suggestions. Thanks to all.
>
> I believe the HIF4's have a bimetal screw which is temperature sensitive.
> It's in the Doohicky which adjusts the main jet. When the car is warmed
> up, it leans the mixture back. I think there is another temperature
> sensitive Doohicky which increases the idle on cold starts (I don't mean
> the fast idle!). Your best bet is to get your car warmed up to the point
> the idle drops below 500rpm , and increase the idle. Of course, your
> idle will be a little high on cold starts. The "book" says to adjust the
> fast idle to 1000 rmp.(we need it here up north!). I don't know if this
> should be set cold or when warm.
>
> I'm having fun with my idle adjustment too. It doesn't help my Tach
> just started acting up. I find the idle is *increasing* after the car
> is run at highway speeds. I find I have to keep the idle up around 800
> rpm (I have upgraded cam and pistins too. ) or she's pretty rough at
> idle. (timed at 14deg static timing) That is supposedly expected with the
> cam I have in.
>
> Just my $0.000002 worth. I'm here to learn.
>
> >
>
> --
> ________ ___
> / ______/ | | Greg A.M.Johnson '72 & '66 MGB
> / \ ___ | | Biology Dept.
> \ \_\ \ /\ __| | Dalhousie University
> \______ / \________| Halifax, N.S., Canada
> \/
> * See the British Automobile Touring Association of NS Home Page!*
>
> http://www.ccn.cs.dal.ca/Recreation/BATANS/index.html
>
>
>
dhall@vcd.hp.com
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