I got new HD8's in 2001 and as I recall they were fine out of the box. I
no longer remember my initial setup mixture adjustment techniques, but
after last year's engine rebuild I couldn't seem to get an idle via the
slow run screw. A good overall mixture was achieved on the engine dyno,
though, using oxygen sensors. A few months ago, I wanted to get back to
basics which is having the jet flush with the bridge and then richening
the screw 2.5 turns. I could not get the jet up high enough to be flush
(instead was .035 down). Thus I asked this list about what depth below
flush corresponds to 2.5 turns. I think I got one response but I dug up
an old HD8 and 2.5 turns corresponds to .060 depth which also
corresponds to a 1:1 lever ratio with a screw pitch of 40 threads per
inch.
Yesterday I found out the two reasons I couldn't get the jet flush and
they are unique to these new reproduction carburetors, not withstanding
using "SU tooling".
1. The Burlen jets are very short. They are 1.145 long. The old SU and
Moss supplied jets are 1.177. That is quite a bit.
2. The lever that holds the mixture screw is not shaped properly. It
interferes with another part of the casting so that the mixture screw
lever doesn't get full travel in the lean direction.
Another area of difference to the original HD8 SU's is the use of metal
throttle shaft bushings and push on rubber seals instead of Teflon
sleeves. After 10 to 15 thousand miles, there is way too much slop in
these bushings, requiring attention. One bushing has quite a large burr
on it and the adjacent rubber seal has lots of cracks that the three
don't. That seal won't last much longer. The bushings are of a split
design, so I guess they have to leak a little bit.
Conclusion: might as well get your old HD8's rebuilt.
Ken Freese
65 BJ8
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