[Spits] 79 Spitfire with SU carbs

[Jim Muller]

I'll give you credit for having the courage to show up on a Triumphs 
list with an MGA! :-)

On 26 Jun 2007 at 17:43, David Woerpel wrote:
> 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.

The fact that it runs with the choke pulled back on suggests that it 
has a bad air leak.  Does it blow black smoke with the choke pulled 
out?  And how much choke too?  Maybe those carbs had really worn 
throttle shafts?  Boy, they'd have to really worn though.

> It ran better off choke momentarily but then fuel poured out both
> float bowl overflows.

The momentary running well was obviously due to the excess gas.  One 
possibility is that the float valves were and still are sticking.  If 
the old pump couldn't keep the bowls full, then adding choke could 
help.  Apparently the new pump forced more gas through the valves.

Even so, a big air leak would still cause that behavior.  Forcing 
enough gas through to spill out of the bowls through the jets would 
enrichen the mixture and compensate for the air leak.  Getting it 
dialed in would be difficult because idle would greatly affected, I 
would think.  Could the vacuum retard unit have a split diaphram?  
(Is it hooked up?)

> The coughing back through the carbs makes me suspect 
> timing but when it runs it's pretty smooth.

Nnnnnmmmm, bad timing doesn't feel right.

> Just for kicks, what are the timing specs for a 79 1500?

Static 10BTDC, dynamic at idle 2ATDC.  Of course, the vacuum retard 
unit has to be hooked up for that dynamic spec to apply.

It's always possible that something else broke, but coincidences 
don't happen in cop shows and detective mystery books.

-- 
Jim Muller
jimmuller at rcn.com
'80 Spitfire, '70 GT6+



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