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Re: [Spits] 79 Spitfire with SU carbs

To: spitfires@autox.team.net
Subject: Re: [Spits] 79 Spitfire with SU carbs
From: David Woerpel <dwoerpel@wi.net>
Date: Sat, 30 Jun 2007 13:49:23 -0500
Thanks Roger.  Here's more pieces to the puzzle.
Owner put on the original fuel pump and no more overflow!  Yay!  The new 
pump we measured at 3-3 1/2 lbs. which apparently caused the overflow.  
Owner then drove the car and it was fairly smooth to ~3200rpms at which 
point it started stumbling so he parked it.

When I got there, we determined TDC and noted the rotor was firing #1 
(Lucas Electronic) as the sensor was opposite the pick-up(not sure what 
the nomenclature is as I'm a points/condensor man myself).  So we set it 
to 10*BTDC and started the engine.  I then reset the mixture and synched 
the carbs.  It ran well and the engine revved smoothly so we took it for 
a drive.  It started stumbling and backfiring ~ 4000rpms but was really 
good up to that point.  So we rotated the distributor a bit and I got it 
up to 5200 before it stumbled.  But once it started to stumble the 
'stumble limit' (not a character from Harry Potter) became lower until 
we were around 4000 again.  The pinch bolt is tight so that didn't slip 
and we drew an index line so we could check for that. 

The stumble or miss almost has me wondering about the ignition or dizzy 
advance.  How does one check to see if the centrifugal or vacuum advance 
is working?  But most important is what is causing the problem at higher 
rpms??

We're getting closer!!   I really appreciate your help and the what a 
great car!!
Dave
Burlington WI

Roger Elliott wrote:
> Hi David,
>
> Thanks for the info.
> 10 BTDC seems to be the standard timing on the British version that 
> had a higher compression ratio than the US.  So I think that is what I 
> would try.
>
> Roger
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