Subject: Re: [Healeys] High speed miss - CARBS? - followup

From: john spaur <[email-masked]>
Date: Mon, 30 Sep 2013 21:58:50 -0700

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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