[Healeys] High speed miss - CARBS? - followup

[Bob Haskell]

John,

The piston/dampers are treated as a set.  That's why the manual said to 
replace both.  You could have tried different piston/damper combinations 
until the drop time was the same for all three.  I've been told that 
it's more critical to have the carbs drop at the same rate rather than 
to be in spec.  But I don't know how far out of spec is okay.

Bob Haskell
AHCA 3000 Mk I registrar
http://www.ciahc.org/registry_3000mk1.php

On 10/01/2013 12:58 AM, john spaur wrote:
> This applies to my BT7 tri-carb.
>
> All of you experts out there provided a lot of helpful information that
> helped me resolve the problem with my carbs. I believe the miss was
> mostly caused by carburetor synchronization although it was in several
> areas.
>
> 1. I had the carbs plated in electrolysis nickel. This changed the
> tolerances between the piston and dashpot. The S.U workshop manual has a
> test and the fall rate needs to be between 5-7 seconds. The fall rates
> varied from 5 to 15 seconds depending on the dashpot. I fixed this by
> sanding the dashpot and or piston/dashpot interface. The S.U manual
> states you need to replace the dashpot and piston, however, because I
> had plated the parts I figured I could fix it and did. There was also
> some pitting inside one of the dashpots that may have affected the
> vacuum when the piston was at a certain position. I filled in the pit
> with JB Weld, which is not an easy thing to do.
>
> 2. The throttle shaft forks were not actuating the throttle plates
> uniformly but adjusting the throttle forks took care of that.
>
> 3. The mixture was somewhat lean and it was adjusted.
>
> 4. The micro timing was off. I worked with the vernier adjuster on the
> distributor to fine tune the timing.
>
> It still misses a little at times, but the problem has been greatly
> reduced and it seems to be going away as the various parts bed in.
>
> Many thanks to all of the experts and healey enthusiasts alike!
>
> John Spaur
> San Jose
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