Since I sent the original note in the heat of the moment, I have been
rethinking a little bit. Let me recap the history. I have had the car since Aug.
1997. The SU setup is from a Mk III, based on the intake manifold having the
hole (plugged) for the emission control valve (but no valve). Car was pretty
peppy and ran well, but would never idle smoothly below 1200-1500 rpm. Idle
adjustment was always strange, with the lion's share of effect on the rear carb
(C2), very little change when adjusting the front (C1). When I got the car out
of storage this year, it ran roughly under acceleration (hesitant and slight
miss). I got the Haynes Spitfire manual last fall, and between it and the
Bentley, decide to try and tune the carbs. First surprise- no hiss at all on
idle on C1, C2 was doing all the work.
I set the idle screws at 1.5 turns after engagement, according to the tuning
instructions, and did the jet adjustment to "flush with the bridge" on both,
then backed off two full turns on adjuster nuts. C2 jet was hard to get up to
flush with the bridge- seemed to be at the limit of its travel. I was then
unable to get the engine to vary up or down much at idle with either C1 or C2,
screwing in or out. Idle was between 2200-3000, and i could back the idle screws
clear out of engagement with the cams before it would come down very much. So
much for turning the jet adjusters "one flat at a time to fastest, consistent
idle".
Have balanced the carbs by intake sound at idle, finally have smooth idle at
900-1100 or so. Idle is great, every other throttle position is terrible. The
choke linkage was also all screwed up, with no movement downward on the C1 jet
when C2 was fully engaged. I adjusted the choke linkage linkage to engage both
last night.
To make a long story short, I think C2 has been running the whole car and is not
adjustable. With C1 on line, the car is drowning in gas when the throttle is
applied.(although I can't say for sure that the miss is due to loading up). The
lack of response to jet adjustment suggests rebuild.
Ted Schumacher and Joe Curry, thanks for responding to my first note this
morning.
Regards,
Bob Waid
71 Spitfire FK4081L
The car
----------
>From: Ted Schumacher <tedtsimx@q1.net>
>To: "R.D. Waid" <msp01091@isd.net>
>Subject: Re: Weber Decision
>Date: Sat, Jun 12, 1999, 8:55 AM
>
>bob, the su's are a better set up - more power - than the weber. we can
>rebuild
>your carbs or guide you through adjsuting the su's. give me a call on our tech
>line.
>thanks and let me know if we can help. ted
>
>R.D. Waid wrote:
>
>> I've decided to bite the bullet and install a 2bbl Weber to replace my twin
>SUs
>> on my DPO-modified Mark IV. This is after a frustrating 2 evenings worth of
>> trying to get them to work together. I now have great idle but missing at
>> everything above idle and no power. I've tried to follow both the Bentley and
>> Haynes tuning procedures, but I think at least one carb is in need of a
>> rebuild.
>>
>> I'm going to try the Performance Parts Warehouse (www.webercarburetors.com).
>> Anyone on the list have firsthand experience with them? Assuming this works
>out,
>> I'll have a pair of SUs (tag number AUD 257R and E) and MkIII intake manifold
>> for sale or trade.
>>
>> Bob Waid
>> 71 Spitfire FK4081L
>
>
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