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Re: SU Carbs- Idle Woes

To: "Allen W." <AJWILLIA@UA1VM.UA.EDU>
Subject: Re: SU Carbs- Idle Woes
From: Greg Johnson <ab916@ccn.cs.dal.ca>
Date: Thu, 2 May 1996 13:08:58 -0300
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.     

> 

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   / ______/        |   |  Greg A.M.Johnson           '72 & '66 MGB
 /   \   ___        |   |  Biology Dept.
 \     \_\  \  /\ __|   |  Dalhousie University
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