View Full Version : SU Carb Help ......

George Zeck
12-29-2003, 03:38 PM
I was able to spend some good time on my project during x-mas -- restoring a 64 Sprite that hasn't run in < 20 yrs. Replaced Tank, fuel line & added new electronic fuel pump. Also rebuilt both carbs with new gaskets / springs / rubber items where required. Car is in FLA and I am in OH and simply ran out of time to finish.

The next "step" is to run the power to the fuel pump & put the carbs on the car and adjust. From past links - I am aware of the need to put a "steel plate" to cover up the hole on the old placement. Run the power in "reverse" (Positive ground) -- pump is SU Pos & Neg from World Wide Auto. As for the SU Carbs .........

Any comments on the SU Carb's ?? I had the jets completely apart and replaced needles, jet's, and anything that was gasket or spring related. Also soaked in parts cleaner to get the "sludge" (formerly gasoline) off. How difficult is it. Any reading someone could recommend would be appreciated. graemlins/driving.gif



[ 12-29-2003: Message edited by: George Zeck ]

[ 12-29-2003: Message edited by: George Zeck ]

[ 12-29-2003: Message edited by: George Zeck ]</p>

12-30-2003, 12:09 AM

Run a white wire from the ignition switch to the fuel pump. White is the correct color on later Sprites. You could run it from the switched side of the fuse block too. (white or green wire side)
Might as well keep it correct.

On the carbs, make sure the jets are centered.
Loosen the large nut a bit, raise the piston (dashpot off) and let it drop, it should clunk.
Do this at the same time as tightening the nut incase id slips. there should ne no binding.
For an initial carb setting, turn the adjusting nut (5/8 wrench) 2 1/2 full turns down.
Or 15 flats of the nut. This is a good starting point. from there it should run, you can lean (tighten) or richen (loosen) the nuts as required
once the car warms up.
Who am I kidding, carb adjustments are a daily chore on SUs images/icons/wink.gif I mean a tweak here, a tweak there, and when you think you have it perfect, the weather changes so you tweak them just a wee bit more.

Mickey Richaud
12-30-2003, 06:34 PM
George -

Here's a great "how-to" for adjusting SU's:

Tuning SU's (https://www.manchester-minis.cwc.net/technical/sucarbs-roger_garnett.htm)

12-31-2003, 01:41 PM
Hello Spritenut,

I was going to reply to your comment, but in stead I will quote what is written in the"Tuning SU's" link. Note the last sentence.

step 1- Tune up the rest of the engine- REALLY! clean or replace, and set the points, set the timing, plugs, valve lash, and remove the air filters (have new ones ready) All of these things can affect the setting of the carbs, which should be done LAST, (if at all). The carbs rarely need to be adjusted, once set.

Alec graemlins/cheers.gif

Mickey Richaud
12-31-2003, 01:48 PM
Well said, Alec. Once I got mine set, they have performed perfectly well (several months now).
Also, remember to keep the proper oil level in the dashpots. The stuff does "disappear" from time to time.

01-01-2004, 06:07 PM
edit: Sorry, it is upset bovine!! After posting this, I read the post just above it and realized mine was un-needed.

It has been a long while so perhaps I'm having brain fade (or could it be "mad cow" or upset bovine??) but I thought one needs to put some light weight oil down the center of the piston under the large hex nut thats located up on top of the piston chamber.
As I recall the oil acts as a damper to slow the pistons rising during acceleration.
Am I wrong??

[ 01-01-2004: Message edited by: XK4 ]</p>

01-02-2004, 04:12 AM
Hello XK4,
no, you are not wrong, that is why the oil is there. There is a small piston attached to that nut and it's function is to stop the piston rising too quickly when the throttle is quickly opened which would then weaken the mixture. It is the same function as an accelerator pump on some fixed jet carburettors.

Alec graemlins/cheers.gif