John said, in part:
>
> The problem, as was hinted at in the Robert Bentley Shop Manual, was the
> Deceleration By-Pass valve on the Carbs. Even though these valves were
> replaced when the carbs were rebuilt, they were stuck wide open - hence
> 1500 idle !!
Having rebuilt a few hundred of these critters, I can assure you that there
is nothing inside that can cause them to stick open. However, it doesn't take
much in the misadjustment department to make them come open at "normal" idle.
I suppose it would be possible to get a piece of trash wedged in them, but in
XX years, I've never seen it happen.
> My mechanic said he has never scene the blasted things work
> correctly in nearly 20 years of Triumph work.
A> make sure the diaphragm is okay, and no pieces are missing.
B> use the correct gasket to mount them on the carb. The carb kit will come
with three or four different ones. *Only* one is right for a given app.
C> Turn the adjuster about five turns counter clock. Set up the rest of the
carb adjustments; mixture, idle, balance. Now do one decel valve at a time.
Turn the adjuster clockwise until the idle starts to rise. Then turn it
slowly counter-clock until the idle falls back to normal, then an additional
half turn. Bring the engine speed up to about 3000, and let the throttle
snap shut. You should be able to here the valve open (chattering hiss) and
then close just before idle speed is reached. The engine speed should drop
evenly; no flareout just above idle. Fine tune as needed.
You now have the correct setting on this one. If there are additional
ones to do, turn the first one counter-clock two turns to disable it.
Repeat all the above steps for the second (and third and fourth). When you
have done all of them, remove the two turn "lockout" from the first victims.
Simplicity itself on a Spitfire. Tad bit more tedious on a V-12 Jag (four
of them, and access is, ummm, limited).
> To fix the problem, he
> somehow blocked them off and the car now runs and idles perfectly and is
> even within emision specs !
Blocking them off is easy, you just make a blank gasket. In some climates and
emissions laws you can get away with it. HC's will be high during overrun only
(do any states check for this yet?), and you may have problems with chugging,
loping, and stalling when closing the throttle quickly with no load. This will
be most evident at traffic lights on hot days.
> John Clerici
> Chapel Hill, NC
> jmcleric@gibbs.oit.unc.edu
Randy
randy@taylor.infi.net
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