Dave:
First of all, have you read your plugs? Make sure that your mixture
is correct - the plug insulator should be the color of corrugated cardboard.
Be sure to check the plugs for BOTH carbs (i.e. each carb feeds three
cylinders, so make sure you check a cylinder from each carb). Use a color
tune if you have one. DO NOT use the "lift the slide" test, as it will be
incorrect if the camshaft is not stock - and cams are often not stock having
been changed by a previous owner. If your insulator is white or nearly
white, your mixture is too lean, and you are getting a lean miss.
Second, have you checked your ignition timing? Disconnect the vacuum
retard, and set the timing at 10 BTDC using a timing light. I recommend this
method because the method in Bentley will not work if the vacuum diaphragm
in your vacuum capsule has perished, which they all have by now unless they
have been replaced in the recent past.
If the above is correct, let me ask this; Is it a stumble or a miss?
Stumble off of idle means that the mixture is not going rich enough, so a
high viscosity oil in the dashpots is probably in order. A miss would be a
slightly different symptom and cure.
If it is a miss, check the following: Set your dwell using a dwell
meter. If your dwell is incorrect, you can get a miss (ask me how I know).
Next, try a different set of plug wires. The standard plug wires are
resistor wires, and the resistance climbs as the wire ages, leading to an
intermittent miss. Next on the list, try a new set of plugs. I had a
resistor plug go bad, and a new plug corrected the miss (you can see that I
have seen engine miss several times on various cars over the years). Last
item to check - make sure that the spring loaded carbon pin in the center of
the dizzy cap is making good contact with the rotor. I had my TR6 develop a
miss because the spring that pushes the pin down on the dizzy rotor was
weak, and I got intermittent contact with the rotor. I suspect that the
rotor may have been a bit shorter than needed, or the cap was a replacement
cap that had a pin that was a bit shorter than the OEM cap. Dunno. But I
know that I stretched the spring that pushes the pin against the rotor, and
the miss went away.
Cheers,
Vance
-----Original Message-----
From: 6pack-bounces@autox.team.net [mailto:6pack-bounces@autox.team.net] On
Behalf Of Dave More
Sent: Saturday, April 23, 2011 12:47 PM
To: 6pack@autox.team.net
Subject: [6pack] SU HS6 on TR6 Needles & Springs
I have some HS6's on my car and the car runs well with them with the
exception
of a bit of a minor stumble off idle. Mixture is correct, the carbs are
balanced, dashpot oil is the correct level, so I'm starting to think springs
and/or needles.
Can any of you running these carbs tell me which springs and needles you're
running?
I got these carbs from Jeff at Paltech so I'll be getting hold of him as
well.
Oh, and FWIW I'm also at about 4000' altitude.
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