« Previous Entry | MAIN | Next Entry »
November 02, 2003
Martyn...you misunderstand.
The spring over the air valve in the SU
carb determines mainly when the air
valve reaches the full open position with
respect to "redline" assuming all other
things equal. This is it's only purpose.
As cam profile duration and lift increase (over "stock") so shall vacuum
produced
by the engine at lower rpms DECREASE.
IOW......at
lower rpm (idle) the engine will "suck"
LESS, all else being equal. With respect
to your problem, vacuum in this case
is working FOR you, not against you.
Make sure your throttle return springs are
properly hooked up and that the air valves
fall freely to the jet bridge when lifted, then released, landing upon
the jet bridge
(engine off, obviously!:) with the appropriate "dull thunk" of metal
contacting metal at low velocity.
If the air valves do not behave as indicated above, then the air
valve(s)
are "hanging up" (the jet(s) within
the carbs need "centering") which will
cause an artificially high idle.
Make sure there are no vacuum leaks and
the throttle cable is PROPERLY SEATED
in it's fitting incorporated in the heat shield (they can come out and
hang up "upon"
rather then "within" this fitting...which WILL cause a case of "high
idle").
(A "sticking" (old/worn) throttle cable could be the culprit as well, of
course.)
There is NO GOOD reason why your engine should not idle perfectly well
at
1,000rpm, Martyn....VP3 cam or not, if
the cam is timed in properly and the
ignition timing is set properly as well.
There is NO MYSTERY here. There is
no reason why the butterflies should not
close completely when the idle screws
are backed off to "less than zero" in
terms of the camshaft you are using...
and the engine should quit accordingly...
.....IOW the camshaft you are using is
NOT, per se, the problem. The camshaft
itself, has nothing to do with your idle
problem.
Cap'n. Bob
'60 :{)
PilotRob@... 26434
Posted on November 2, 2003 08:30 PM
Posted to category(s) Carburetor | Cylinder Head | Electrical System | Engine (external) | Engine (internal) | Ignition System | Intake System | Miscellaneous | Restoration | Suspension & Steering | Technical Info | Tuning
