K_Reparaties - K_Repairs (24.05.2008 )

Problem K: SU-Carburettors (added 14/01/2006)

Recently wrote this and got the advice to publish it on the site:
There's nothing much that can go wrong with an SU and to deal with feeding an engine the right mixture they're a marvellous discovery..

Three normal maintenance checks:

1 There should leak no NO fuel out of them.
    Dangerous spots:
    1 upper side of the floating chamber (where the fuel-lead goes in)
    If it leaks there then needle that should prevent too much fuel coming in doesn't stop the fuel enough
    Means new needles and seats. part #5 (see picture SU_6) (if it leaks there it leaks through a small venting hole)
    Small possibility that the pressure from the fuel-pump is too high, read the manual to check the pressure.
    2 if it leaks on the rubber tube from the underside of the floating-chmber to the jet underneath the carburettor
    Means new jets part #4
2 You should try to locate the "piston lift pin" it sits underneath the suction chamber and is only there for diagnostic reasons
    First test is alsways (engine not running) to push the pin up to lift the piston, if you let go of the pin you should hear a "tick" by the piston falling back on its resting position.  If you can't get the piston up or you don't hear no tick the alignment of piston - needle - jet - suction chamber is wrong.
 
3 Check if there's still oil in the damper on top of the carburettor (unscrew the black button and pull out the damper).
   Engine oil will do - there's explanation in the text.
 With a warm engine running at idle speed: if you push up the piston lift pin for two seconds and then drop it again, the rpm should go up quickly and drop shortly after you let loose of the pin.
If it raises but stays high your mixture is too high, if rpm drops instead of climbing mixture is too low.
But these are rules from the days that mecanics didn't have no CO-gauges and everything had to be done on intuition, the lifting pin gave good diagnostics then. If an engine is trimmed with nowadays diagnostic devices idle rpm is much higher and mixture is much lower at idle speed.  When I go to MOT I trim my jet-adjusting-screws 7 half turns up to make the mixture poorer, same time I have to adjust my throttle adjusting screws to keep the engine running and it must run on higher rpm then, afterwards I re-adjust them to get the "pof-pof-pof-pof-idle.
 like it when I can count the rpm's.

Last thing you can do is to put your ear against the air-inlets (or use a water-tube as is indicated in the text).
Both carburettors should make the same "hissss", this you can do at different rpms, if they're trimmed wrong there's an obvious difference.
To learn how to recognise the difference you can use the lifting pins to make difference.

If at idle speed there's not too great a difference you can probably adjust the hisss by turning the throttle adjusting screws.  If you can't get it right could mean the balance of the carburettors was set wrong, and if it had been right could indicate serious problems - wear at valves or pistons.

Problem K: SU-Carburettors (added 28/09/2006) Throttle retractor springs

While on the way to Goodwood early september 2006 when I lifted my right foot to slow down the pedal didn't follow anymore.  One of the springs that should close the throttle when the pedal is not pushed, had broken. I was following André and we were both lucky that I didn't follow him too close. A nowadays car should have been towed home but I managed a quick repair and after the meeting and a lovely vacation in UK I went for a replacement.  As allways I did lots of shops and bought some 25 different replacement springs that would all have worked but I had rather found some identical ones.  At last found the closest fit with Hillaert (see adresses).  

The springs on my car (don't know if they are original) were made of a thread of 0.8mm thick, external diameter of the spring 7,45mm wide, length of the body of the spring (all windings next to another) was 56.5mm, and the hooks were adding +/- 5mm to the length of the spring. The ones I have fitted now are made of RVS - "rust resistant steel".  In Belgium we call it INOX(idable).
Haven't driven the car since, but it looks nice (shiny). For about some 20€ Hillaert would remake any pair of springs of about that size.
Fitted the "Hillaert"-springs because they were closest (identical) to the original. Perhaps RVS is harder and will brake sooner than 30years of pushing the throttle.(Jef Neefs)

 

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