[Healeys] HD8 adjustment

BJ8 Healeys sbyers at ec.rr.com
Sat Apr 7 10:53:23 MDT 2012


Gary, being frustrated with the clarity of available instructions for
adjusting HD8 carbs in the SU and workshop manuals, I wrote my own
procedures for doing the job and illustrated them with photographs.  These
instructions are available on the web, and I recently heard from someone who
was using them but running into the same problem you describe.
He says that he cannot get the car to idle fast enough with the fast idle
screws backed off completely and running on the "slow run valves" alone (the
big idle screws).  I have not personally run into this before, nor have I
heard from anyone else who has used the instructions that they have the
problem, either.

The car in question is a new one to the owner, so we don't know what
condition it was in when he bought it, nor do I know at this point if the
preliminary adjustments (valves adjusted, timing checked, ignition
components in good shape, etc.) have been done/checked, or if the initial
settings of the Jet Adjusting Screws (2-1/2 turns clockwise (rich) from jet
flush with the bridge) or the Slow Run Valve adjustment of three full turns
counterclockwise from the seat have been done.  For my own car, the initial
setting of the Slow Run Valves is sufficient that I have to turn the screws
down to slow the engine to the idle speed setting of 500 RPM.

I would be interested in the responses to Gary's question also.

Steve Byers
HBJ8L/36666
BJ8 Registry
Havelock, NC  USA

-----Original Message-----
From: healeys-bounces at autox.team.net [mailto:healeys-bounces at autox.team.net]
On Behalf Of warthodson at aol.com
Sent: Saturday, April 07, 2012 8:50 AM
To: healeys at autox.team.net
Subject: [Healeys] HD8 adjustment

When adjusting HD type carbs, I generally prefer to back off the fast idle
screw so that the throttle is fully closed (after disconnecting any
interconnecting linkage) & attempt to set the idle speed with the idle
screws.
I have no trouble doing this with HD4 & HD6 carbs. Including tricarb cars
with both HD4's & HD6's. Yes, I know those are not the original tricarbs. My
problem & question concerns the HD8's which seem to defy being adjusted this
way. I never seem to be able to open the idle screw far enough to increase
the idle speed to an acceptable level. In many of these cases the HD8's have
been recently fully restored professionally & the cars are in very good
condition.
Am I correct in believing that this is a common problem?  If yes, what are
the theories that explain why HD8's behave this way? Yes, I know there are
two (or
more) schools of thought on how to adjust carbs.
Thanks,
Gary


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