I did'nt blank mine off so much as I adjusted them till they could not
open(under any circumstances). Its my understanding they are a very minor
emission add on to allow extra air into the carbs when the engine is in
deceleration(i.e high vacuum which opens the valves if they are adjusted
correctly). Having them adjusted to never open eliminates the possibility of
opening when at idle(or any time). If their open at idle, they allow extra air
into the carbs and like any vacuum leak, this raises the idle dramatically. If
you want to you can try to adjust them to open only on deceleration. If so,
make it for hard high rpm deceleration(ie. so they barely open) so you can
insure they are shut at idle. How do you do this, make another quarter to half
a turn above the recommended turn listed in the Bentley book. Of course if you
go to far, you effectively do what I did and make them never open at all. If
your trying to solve a vacuum leak(and it sounds like you are) I'd set them to
not open first and see if that solves the 'leak'. If not, leave them shut and
look for a leak elsewhere. On the heals of a rebuild your gaskets/diaphragms
are all sound then the suspects are temp. compensator, bypass valve, old vacuum
hose with a crack somewhere.
On Wed, 16 Jun 1999 05:39:44 john donohoe wrote:
>Um, I've fully rebuilt the ZS emission carbs on my GT6+, and the only
>way I could get the idle down was by blanking off those bypass
>Can you explain why blanking the bypass valves helps the high idle
>problem, and also suggest what the *real* problem might be? Blanking
>the valves works great for me, but it seems to be a "work-around" and I
>would much prefer to solve the root problem!
>--- Atwell Haines <firstname.lastname@example.org> wrote:
>> You may be the 'victim' of multiple problems.
>> Now that the choke is out of the picture, it sounds
>> as if the
>> bypass/deceleration valve is bad. That's a common
>> cause of a 2000 to 2500
>> RPM fast idle.
>> Got any gasket material left over? Blank that b/d
>> valve off and see if
>> your idle returns to normal...
>> BTW if you are looking at the Bentley manual, be
>> advised that the pic of
>> the idle speed screw is misleading. The
>> spring-biased 'idle' screw is for
>> the _choke's_ fast idle; the actual idle screw is
>> the slotted headless
>> screw just forward of the other one. It has a 3/8
>> locknut surrounding it.
>> (This drove me bonkers for a while last year during
>> my 'learning' phase.)
>> Back that off before you muck with the bypass valve.
>> You won't mess anything up by covering all the choke
>> holes with your
>> blanking gasket. And no, I don't know why they want
>> the throttle propped
>> open, unless its to make removing the choke's
>> linkages easier.
>> Atwell Haines
>> '79 Spitfire, converted to manual choke, no beer
>> cans used at all.
>> Succasunna, NJ USA
>> "When everything's coming your way, you're in the
>> wrong lane, going the
>> wrong way."
>> At 04:53 PM 6/15/99 -0700, John Weale wrote:
>> > In my quest for a smog certificate, I blanked off
>> the water
>> >controlled choke in my Spit (using some gasket
>> material, though I was
>> >sorely tempted to use a bit of beer can just for
>> the heck 'uv it). Now
>> >the idle is around 2400 rather than the 1100 it
>> started at. I adjusted it
>> >down via the throttle speed screw, but am concerned
>> that I screwed
>> >something up. When removing the water choke, I did
>> not hold the throttle
>> >plate open as the manual (dug out after I did it of
>> course) instructs.
>> >Any idea why it says to do this? Is it reasonable
>> to hope that the choke
>> >was stuck open and blanking it off simply fixed the
>> mixture (it did fail
>> >smog due to high CO and HC's perhaps this
>> contributed?)(hey, I can dream
>> >:), raising the RPM's? Is blanking off all the
>> holes between the carb and
>> >water choke OK (I assume so, but that's gotten me
>> into trouble before)?
>> >Thanks for any advice!
>> >John Weale