[Spits] 79 Spitfire with SU carbs

[Roger Elliott]

I have been chasing similar problems for quite a while.  It never 
occurred to me that the problem could be too high of fuel pressure.

What did you need to set the pressure at to make the car run correctly?  
I stopped at Napa, they had one that could be adjusted 2 - 4 pounds and 
one that could be adjusted 4-9 pounds.

Thanks,

Roger Elliott

Paul Meyer wrote:
> 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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