[Spits] 79 Spitfire with SU carbs

[Paul Meyer]

Several years ago I swapped carbs on my '78.
Similar fuel problems resulted, which were eventually identified as being 
caused by the new carb requiring less fuel pressure.  Idle was ok, but as 
soon as I increased rpm or fiddled with the choke, it would roughen or 
stall.  I too replaced the fuel pump, but that only made things worse.


I put in a cheap, in-line fuel pressure regulator, and got some improvement, 
but the cheap regulator caused flow problems in high rev conditions.

Ultimately, I put in a higher quality fuel pressure regulator, and that 
solved it.



Paul F. Meyer

Home Phone:    781-551-8574
Cell Phone:       781-801-3170
e-mail:               paulfmeyer at msn.com




----Original Message Follows----
From: David Woerpel <dwoerpel at wi.net>
To: spitfires at autox.team.net
Subject: [Spits] 79 Spitfire with SU carbs
Date: Tue, 26 Jun 2007 17:43:27 -0500

Hello,

I am helping a friend with a 1979 Spitfire 1500.  He's removed the
Zenith and installed 2 S.U. HS4's.  I'm one of the masochistic types
that likes working on SU's and have no problem with the H4's on my MGA
or H1's on the Bugeye Sprite but this problem has us stumped.

The car has been desmogged, the head lightly shaved (I don't know how
much) and the rest is stock as far as we know.  It was running happily
and he decided that he wanted SU's.  The carbs are set correctly. We
started with the jet adjusting nut at 12 flats down (yes, they are
centered).  The float levels are at 3/16", oil in the dashpot (1/2"
above tube).  The car starts and runs on choke and the pistons rise
equally but when the choke is gradually reduced after, 3-5 min., it
starts to stall.  Add choke; it runs.  Push off the choke and it wants
to die.  When we tried hand manipulating the throttle it occasionally
coughs back through the carbs and dies.

The owner had ordered a new mechanical fuel pump which we installed.  It
ran better off choke momentarily but then fuel poured out both float
bowl overflows.  I know the mechanical pump isn't putting out too much
pressure so I'm suspecting the float needle and seat.  New rubber tipped
ones are on order.  The coughing back through the carbs makes me suspect
timing but when it runs it's pretty smooth.  Just for kicks, what are
the timing specs for a 79 1500?  He has no manual and mine are for my
above cars.

Any suggestions would be very helpful.  Thanks in advance.

Dave
59 :{)
59 MGA 1500
05 MCS
Burlington WI
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