Proper SU Adustment

[kkaa]

At the final tuning phase of our restoration, getting closer to our real maiden voyage but need clarity.

Ive watched a few videos on tuning the carbs and used the link below and am now a little confused.

The way im reading the instruction in from SUCarbs in the UK, their instruction for dual HD is that the the fast idle screws are used when more than one carb is inline, and the slow running valve completely closed?

Just want to make sure, and for us we decided to use a ColorTune for adjusting the Jets..... Hope this is a good question...



https://sucarb.co.uk/technical-hd-type-carburetter-tuning-multi
Note: Whenever the throttle adjusting screws (3) are fitted they, and not the slow-running valves, must be used to adjust the idling speed. Screw down the slow-running valves (which must remain closed) and set the throttle adjusting screws (3) 1.5 turns open. In items 2 and 3, adjust the idling speed with the throttle adjusting screws.

 

[AH100M]

Which Healey?

 

[kkaa]

60' BN7 with HD6 Su's. For the most part, all stock, recent rebuild of carbs from Dana at Sucarbs in US.

Timing set at 35 all in, 3500rpm, (VAC plugged during setting), pertronix ignition, plugs gapped at 32.

Which Healey?

 

[DerekJ]

The SU description and diagrams can be confusing. If memory serves me the standard SUs fitted to Healeys did not have 'the throttle adjusting screws'. Each type of SU, whether HD6 or HD8 etc, has a whole range of variants. I think there are about 25 different types of HD8 that were used on different Jags, Astons, etc. some of which do have throttle adjusting screws.

 

[steveg]

I'm on a road trip and don't have the factory manual, but what the Burlen link says about the throttle adjusting screws is surprising because it's opposite to the manual, which says do the idle adjustment with the slow-running screws. Throttle adjusting screws backed off enough to have a few thous clearance with throttles closed. Throttle screws act as fast-idle when choke is pulled out.

You can use a dial caliper on the main jets. Start with .055" drop from the bridge. Use the caliper to check that both jets are equal.
Clockwise = richer, btw.

Another thing is our cars don't run that well with the current ethanol/gas mixture. I didn't find the ColorTune that useful because the car didn't run right unless it showed way-rich on the colortune -- your mileage may vary.

If you don't have it, buy Norm Nock's Healey book from British Car Specialists - it has most of the tips you'll need in one place.

 

[DerekJ]

Steve. The manual says use the slow running screws because the HDs fitted to Healeys don't have 'throttle adjusting screws'. I have a copy of the SU workshop manual. Page 26 re: HD Type Reassembly, shows an HD carb and indicates the Slow running valve and the fast idle screw. There is no 'throttle adujusting screw on the model shown which is the same as the ones on Healeys. Page 28 shows a diagram of a carb with the Throttle adjusting screws and this is where the notice is printed about not using the slow running valves. Part of the confusion arise because some people confuse the fast idle screw with a throttle adjusting screw, but they are not the same thing. Interestingly I just sold a set of HD8 carbs which did have the throttle adjusting screws. They had been put on my car by Jeremy Welsh when he built up the engine. They probably came from a Jag.

 

[DerekJ]

...that's Jeremy Welch!

 

[John Turney]

Adjust the idle with the slow-running screws.

I have a pair of Colortunes. I put one on #2 and one in #5. They work great for me.

 

[kkaa]

John, any reason for using 2 and 5? I was thinking of starting with 1-2-3 on the front carb, and 4-5-6 on the back would all get the same results?

Adjust the idle with the slow-running screws.

I have a pair of Colortunes. I put one on #2 and one in #5. They work great for me.

 

[John Turney]

Because they are the middle carbs in each bank.

You can do each carb individually and average the results for 1-2-3, or some other variation, but I use two to see any cross effect between front and rear.

 

[kkaa]

Heres a couple pics of the carbs....Basically, what im reading in the manual is different than on the link I provided, and again a little different than what I thought, so all is correct in the universe. The "simple" adjustment that the manual says has us a little a-mess

- Yesterday, we had the stock setup, took the pots off, set the slow run valve 2.5 turns from closed, jet the same.

- Installed the pots, without oil, piston dropped freely with a nice "clunk"
- Added 20w, fired up.
- linkage to throttle disconnected, between carbs disconnected.
- Warmed engine, shut down
- Installed Colortune in #1, orange at first, leaned out till blue, all good (If you gus want a video, let me know, really cool)
- Installed Colortune in #4, hoping each SU controlled 1-3, 4-6 and was orange, but could not adjust jet to blue....

Heres the pics of the screws..... And again, the above link says screw down completely slow run valve and use throttle adjusting screws, which you can see are not in use at the moment.....

 

[kkaa]

Ok, let me try 5 instead of 4, because 4 I couldnt get it set to blue...

If anyone wants me to video it, let me know.

Because they are the middle carbs in each bank.

You can do each carb individually and average the results for 1-2-3, or some other variation, but I use two to see any cross effect between front and rear.

 

[steveg]

Derek - I'm off in the hinterlands without any manuals. The use of the Slow Running valves is very confusing in the Burlen directions. They say to adjust the Throttle Adjusting Screws then adjust the Slow Running Valves. My car had HD6s now has HD8s - they are all per the pictures above with the Throttle Adjusting Screw. Wonder what Norm Nock says?

 

[DerekJ]

Kkaa The photo you posted shows the 'fast idle screw'. That is NOT, I repeat NOT the 'throttle adjusting screw'. HD carbs with throttle adjusting screws also have the 'fast idle screw' and slow run valve. I believe you are confusing your fast idle screw with a throttle adjusting screw that your carb does not have. Most HD carbs do NOT have throttle adjusting screws.

 

[kkaa]

Derek!!! Thank you for that.

So, it looks like i do indeed use the slow run valve to get to about 5-700 RPM, make choke adjusts, then use the fast idle to get to 1000 per the link.....

Ill give it a go tonight with the kids and let you know how we do....

Kurt

Kkaa The photo you posted shows the 'fast idle screw'. That is NOT, I repeat NOT the 'throttle adjusting screw'. HD carbs with throttle adjusting screws also have the 'fast idle screw' and slow run valve. I believe you are confusing your fast idle screw with a throttle adjusting screw that your carb does not have. Most HD carbs do NOT have throttle adjusting screws.

 

[CrashTestJason]

Adjust the idle with the slow-running screws.

I have a pair of Colortunes. I put one on #2 and one in #5. They work great for me.

I have just done exactly the same thing with my BJ8.

The carbies were way out of whack. It turns out that the person who previously worked on the carbies (I only bought the car a couple of months ago) had no idea what he was doing. The fuel mix was not adjusted at all. Instead the carbies were made to run by cranking up the fast idle. It ran very rich and was difficult to start and backfired a lot.

I recommend the article at https://www.healey6.com/Technical/HD8.pdf I found this brilliant and easy to follow (unlike the various manuals around)

After following the instructions in the article I finished off by using 2 colourtunes in 2 & 5 (I selected 2 & 5 because they would seem to line up most directly with the respective carbies and they are just easier to get to than 1 & 6).

With the colourtunes in place I adjusted the carbies until they each showed blue and showed the same responses over the rev range and acceleration.

The car runs like a dream after doing this and I am very confident that the carbies are operating in balance.

I had originally taken the car to a so called classic specialist but he had no idea about Healeys or SUs so I drove the car out of there again. After asking around and finding that no one really had any recommendations for a mechanic, I decided to get the colourtunes plus a carby balancing test kit (wires) and did it myself. At about $150 for 2 colourtunes plus the wire kit, I'm sure it cost a lot less than the "classic" car dude would have charged me and I don't have the confidence that he would have got the same level of balance that the colourtunes allowed me to get myself.

 

[steveg]

SNIP...
I recommend the article at https://www.healey6.com/Technical/HD8.pdf I found this brilliant and easy to follow (unlike the various manuals around)

That is a really comprehensive article. Thank you for linking to it.

I would add:
At a dyno session a couple of years ago at APT Performance Technology they recommended:
https://www.aptfast.com/
They recommended as a final step after the tuning process to take a dial caliper and equalize the jet drops. For example if one jet is down .080" and the other is.090" to set them both at .085"