Hi, Earl -
I agree with you that too high an idle speed can promote dieseling. Also
high compression and low octane gas.
I have several sources for carburettor tuning (Haynes SU Carburettors Owners
Workshop Manual, Glenn's A-H Repair and Tune-up Guide, Chilton's Repair and
Tune-up Guide for the A-H). Given that the procedures in none of them are
completely unambiguous and clear (some of them actually conflict), as I read
them it says to adjust the idle speed with the throttles closed using the
"Slow Running Valve" to achieve 600 RPM (or 500, or 1000, take your pick)
while balancing the airflow in the carbs. I'm assuming this low RPM is to
make sure the mechanical advance of the distributor isn't affecting timing.
To finish up, all of the sources describe adjusting the choke and then
setting the idle with the fast-idle screws to give 1000 RPM with the engine
hot, which is what I do.
Because of the inconsistencies (even the same manual uses different
nomenclature for the same screw, for example) and ambiguities, I
consolidated the three sources into my own procedures for my own use. These
have worked well for me, but I'm always willing to learn something if I am
interpreting the process incorrectly. I know my BJ8 doesn't want to idle
very smoothly at 600 RPM though.
The funny thing is when they tell you to lift the pin 0.031 in. - 0.8 mm.
Yeah, right!
Steve Byers
HBJ8L/36666
BJ8 Registry
Havelock, NC USA
-----Original Message-----
From: owner-healeys@autox.team.net
[mailto:owner-healeys@autox.team.net]On Behalf Of Earl Kagna
Sent: Friday, June 23, 2006 9:59 AM
To: Gene Montresor; Healey List
Subject: Re: Dieseling
Gene:
The biggest reason I have found for dieseling on BJ8's is too fast an idle
speed - for one reason or another.
The HD8 carb is designed to idle with the throttle plates completely closed,
on the idle air bleed circuit, which bypasses the main circuit (adjustable
with the air bleed screw). I have found many BJ8's set up to idle on the
fast idle screws, which work by holding the throttle plates slightly open.
Another disadvantage - the fast idles are governed by the choke control, and
we all know that they never really return reliably to the same position
every time, don't we!
Assuming that the timing and mixtures are set correctly (and that the engine
is otherwise healthy - no air or vacuum leaks, etc.), with apologies to
Steve - a correctly set idle speed of 600 - 700 RPM should solve your
problem, or at least point you in the right direction. Be aware that most
BJ8 tachs that have not been rebuilt are likely not accurate - in fact
sometimes wildly so. Use a tune-up instrument with a tachometer function.
Earl Kagna
Victoria, B.C.
BT7 tri-carb
BJ8
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