SU Carbys

[fizz]

Are the SU carbs good and relaible, how is it in fuel and performance wise. I am getting some of Dads mate. What do you guys think?

[oldschool]

Ask Paddy, he's had lots of problems with his 1300 one, which was the main NZ Avenger model to have an SU carby.
A single 1.75" SU was fitted to the last of the Alpines in 1976-77 (replacing the twin 1.5" CD's) and super rare now!
The NZ Chrysler Avengers all used single 1.5" CD's.

Avengers seem to suit the CD's which aren't a bad carby...just 40 years old now and worn throttle spindles will make your car run like a bag of sh*t.
Changing twin CD's to twin SU's will require using 2 left flange 1.5" SU's, as the Avenger twin inlet manifold is setup for left flange 1.5" CD pairs /   / whereas twin 1.5" SU's are often left and right flange pairs  /   \

I've noticed the cable operated single and twin CD's wear the throttle spindles a lot faster than the rod operated single CD's do, as the rod operation is a smooth rotary one, while the cable is always pulling on one side of the shaft causing wear.
Some manufacturers lessened the carby wear problem by fitting a circular cable guide to the throttle spindle, to make the action more rotary.

[Paddy75]

All I know is that with the SU HS4C the 1300 is less jerky at low speeds and seems to be more keen to pull at low revs also.
They were alse fitted to 1600cc engines, I seen a picture of an automatic automatic with the SU. I'll check the Haynes manual. I seen the 'AUD690' on ebay and the seller didn't realize how sought after they are so I bought it to see what would happen. The original SU on my Avenger was pretty well worn out and as far as I can tell, had gotten badly fouled because the blanking piece fitted to the air cleaner was missing (the hole that suits the vent on a Stromberg) so the piston chamber/dashpot someone had cleaned using sandpaper!
That and the jet was done for. It was running rich with the mixture off the run of the screw.

So I blocked the hole on the air cleaner with a bit of tape and cleaned up the new SU. The 1300 seems a bit faster and more eager at 50-60mph than before.
The plugs are a good shade of grey/brown and I can see though I need a decoke (from 5?,000+ miles running rich on the old worn out SU)

Then I fitted the electronic ignition and took the plugs gap to 32 thou, that made the world of diffrence. I even could lean the idle mixture considerably. I found that the throttle response also was very sharp - little movement gave a lot of go so I changed the needle from ACA to ACE, this let me lean off the mixture a little more and the throttle response seems to be much more normal.

BTW I was setting the mixture by the lifting pin method, seems to work as the plugs are not indicating any signs of running too lean.

I'll finish my work in Dublin on the 10th December for a couple of weeks so its off with the Avengers head for a decoke and a look at the valves.

[hunted]

SUs are amazing. Id put them on every car if I could. So easy to tune. May or may not give better performance but I adore them purely for ease of tuning.

[azza1600]

I fully agree, I've been trying different needles in my HS6 and Its amazing the change in performance, its like driving a different car an still I think I could get it beter still, so many needles so little time lol, I even changed profiles of some of them..Its fun when you get a great result

[oldschool]

It's very important to mod the carbies when fitting extractors to Avengers, as you lose the inlet manifold hotbox when the exhaust manifold is removed, cooling the inlet manifold down and dropping 4hp...see David Vizards tuning tips...

http://www.eurospares.com/graphics/engine/Vizard/In%20cylinder%20Turbulance%20and%20Combustion%20Dynamics%232%20-%20GoFastNews.com%20-%20All%20Racing%20News%20All%20the%20Time!.pdf

[azza1600]

This is true, very good read that, I was thinkng of getting rid of my extractors and going back to factory manifold, I dont see an performance increase with them, I think they better than my extractors

[Paddy75]

Right I think I have finally got the carbie on my 1300 right.

For any of you with the AUD690 SU HS4C carbie.

Both 1300 & 1600 had them fitted S5 & S6 and early MK2's. Was fitted to improve economy apparently.
Both the 1300 & 1600 have the same needle it is the spring that is diffrent - harder on the 1600 b/c of more suck I guess.
They do seem to run a bit better than the Stromberg - that is only what I have found.

Fizz, here are a few tips to check your SU.
Take off the piston cover/dashpot and look to see if there are still rings on the inside about 3/4 an inch apart running around the inside of the cover, if so good.
Look at the piston edge where it slides up and down inside the cover, there must be no scratches or pitting. The air gap betweeen the piston and cover is critical.
I have three SU's for Avengers because of ebay, the original on the car and one a neighbour gave me.
I cleaned out all three pistons and covers and from switching around I found the best fitting combination. The piston should move freely with a noticable air drag, if its too little drag the carbie will run rich.
If you think you are running bad then find a Mini agent and get a new HS4 cover and piston, or root about a few old Mini/Leyland cars in the scrapper.

Clean the cover as best you can and do not be tempted to take sandpaper or any abrasive to it. Meths is the best.

Use bicycle chain oil in the damper not engine oil, again this would make it run rich.

When then setting the mixture do so with the engine warm, not hot as Richard says they do run the best a bit on the cool side.
Best to fine tune the mixture after a free light run on the road.
Set the idle speed 770-800rpm then adjust the mixture using the lifting pin, when lifting the piston at idle, when you hear a slight momentary increase in the idle speed you are on target.
When slightly lifting and the speed decreaces - too lean.
When it increaces constrantly - too rich.
Its that easy. Assuming the engine is timed right and not coked.

Also it could be a good idea to replave the needle valve in the float chamber with the ball valve upgrade type. Doing this stopped the slight fuel smell in the engine bay of mine and it'll drop the fuel level in the chamber slightly also. Change the float chamber gasket also.

After fitting the better operating cover and piston combination the 1300 is running a bit better and I notice that at 1500rpm the piston is lifting a bit higher - good news.

At 50mph the enging just wants to pull and pull!