BrickBoard Archives
The files contained in this listing have been automatically archived from the active forums. Because the vast majority of posts are now in one place, this archive is considered legacy. You should use the SEARCH feature OR choose your topic and select date tabs within the forum you choose.
curb idle not returning on SU[1800/69] posted by David Davidson on
Sunday, 11 April 1999, at 3:30 p.m.
Hi,
in this first week of driving I seem to be shaking out every problem. Now it is my twin SU's. The idle speed is fine when I first start up and drive around in 1st and 2nd. However, if I jump on the highway or take it up to 60, the idle does not return to the lowest revs. I will gear down, come up to a light, push in the clutch and the engine is still reving away. If I pop the gas pedal the revs go up but return to the high setting. Only thing that stops it is if I drive for awhile or stop the car and restart it.
Now my gas mileage is also terrible but it could be from the above problem.
Any idea what this is? Is there a fast idle adjustment screw, and if there is, does it change both carbs or do I have to do them separately?
Apart from lots of minor warts the car seems great and certainly turns alot of heads.
DD
Re: curb idle not returning on SU[1800/69] posted by George Downs on
Sunday, 11 April 1999, at 5:32 p.m.
There are a lot of things that could cause this.
I am assuming that this car was originally equipped
with Carbs, probably HS6, but maybe HIF6. In
either case the same things would probably apply.
First possibility that comes to mind are the return springs
that go between each carb and a big washer with an ear
on it held down by manifold mounting studs/nuts.
Each carb should have one and they should be fairly
tight.
Another possiblity is binding or maladjusted linkage.
As you mention there is a fast idle cam on either one
or both carburetors and they sometimes do stick.
When you push your choke in it should turn the fast
idle cam to where it doesn't touch the screw that
rides against it, or at least doesn't lift it. It may be
that your choke cable is loose and only pulls but
can't push (rides up out of the cable stop instead).
Then there is the possibility of vacuum leaks which
can cause erratic idle.
Getting inside, it is possible that you have loose screws
on one or both of your throttle butterflies. If the butterfly
disk shifts a little out of position it will NOT close all
the way.
I hear a lot of comments about the difficulty of synchronizing
carburetors but I think the problem is greatly overstated.
Topi recommends adjusting the idle by ear using a piece
of tubing stuck a little way into each carb in turn (the other
end in your ear) and with the linkage disconnected, adjust
the carbs for a smooth idle at a reasonable speed and
the same airflow sound from each. Once you get this
done install the linkage so that both throttles come off
the stop together and that is all the sync that is required.
I haven't mentioned float levels but if they are too high
they may cause bad mileage and other problems which
might include erratic idle. You should probably look for
signs of flooding (gasoline smell, visible vapor in carb
throats, dripping float chambers or overflow fittings, etc.)
If this is evident look for either leaking or loose float
valve or maladjusted float level. While you're there look
for sediment and corrosion in your float bowls and clean
them out.
George Downs Bartlesville, Oklahoma