You have to loosen both throttle spindle clamps and both choke spindle
clamps, otherwise one idle screw can be operating the other carb, or the
throttle cable may be holding them open. You do not tighten the screws
again until you have adjusted each carb for mixture and idle, then you check
air-flow again at about 1500 rpm to check they are balanced off-idle as well
as on idle. Ditto choke. If you alter one carb for mixture you must
recheck the other, since they are interdependant. If you adjust the second
carb you must check the first again and so on. You can't balance the
mixture properly with a Colortune, you have to use the lifting pin and ear
method. Finally there must be some free play in the throttle cable to
ensure the throttle cams are resting on their idle screws and not hanging
off the cable, there should be a .012 clearance between each lever link pin
and the lower arm of its respective throttle lever fork, the book says.
When both carbs are properly balanced for both mixture and airflow you can
use a Colortune then, or a CO meter, but you must always adjust both carbs
by the same amount in the same direction or you will unbalance them again.
PaulH.
----- Original Message -----
From: Steve Shoyer <Steve@shoyer.com>
To: <mgs@autox.team.net>
Sent: Sunday, July 23, 2000 5:06 AM
Subject: Idle too high on HIF-4
> My Carbalancer finally arrived, so I tried tuning the HIF-4 carbs that I
put
> on my 1980 MGB today. The idle had been running at about 1200-1800 RPM,
> which was much higher than I had wanted. However, after balancing the
> carbs, the lowest I was able to get was about 1200. I was only adjusting
> the idle screws; the fast idle screws were not touching anything, and I
> didn't play with the mixture screws, having set them when I last tried to
> tune the carbs with the Colortune. The front carb seemed to be running
> richer than the rear carb, so the idle screw on the rear was down about
1/4"
> while the front screw was not protruding at all.
>
> I haven't taken these carbs apart, so I don't know which needle they have.
> When I bought them, the PO said that they had been professionally rebuilt
> and had passed the CA emissions tests easily, so my assumption was that
they
> were set up right.
>
> I had set the timing before (about 14 BTDC), although I haven't checked
the
> valve clearance in a while. I believe that both of these are supposed to
be
> done before tuning the carbs, so I know I haven't been thorough. There
also
> was an air leak around the intake manifold which I think I fixed, but it
> could still be leaking a little.
>
> The car seems to run OK other than the high idle. Any suggestions on what
I
> can do to set the carbs up correctly? Thanks.
>
> --Steve (1980 MGB)
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