dual carbs

[Laecaon]

I dont run chokes on my SUs. They were half a turn rich in the winter. 28 degrees outside, and I could start my car in 1 revolution of the motor, and it would idle, though that idle was 450rpm, it would start and idle fine. Warm idle was 700rpm though so I couldnt have been too far off. I learned I could time cranking the motor over while pressing the gas pedal. It seemed as if there was a sweet spot where the motor fired instantly.

During the summer say April ish, I leaned out the carbs. They never required chokes.

Even after I had pulled my motor, and then reinstalled it 1.5 months later, it started first try.

I once changed my fuel filter in Napas parking lot. The car ran for 10 minutes with me blipping the throttle before it even pulled any fuel into the filter.

[Converted_to_datsun]

Hs2? Damn... Hs4 are the 1.5" ones, hs2 is 1/4. I did say hs2, the bolt holes and vents will line up but the center would have to be made a little bigger. The British carb sizes are funky :/ if the haven't shipped you can probably change the order but if they have they will still work

[Laecaon]

bad josh. bad. lol

[Sealik]

Wayno....I can see you dropped the front SU mixture screw(seat) a tad more....relative to the rear one
This tells me your bushing and or throttle shaft is NFG.....<....leaking air.


Also.....

Flatcat,,,,
"I had 40mm Roadsters on the LZ23 521.
It felt like it was running rich big time.

Unless you're packing one hell of a motor with big valves/cam and exhaust 46s are too much."

When SUs are 'retrofitted' for different applications....a wideband is a must.
Needle profile can remedy any lean or rich conditions.
Early 46mm SUs were designed for an L24???.......LZ23 is not too far behind in CCs
Add some headwork....etc....and these SUs can and did run lean in my app...... and have to be tuned.
I have a brand new 38/38 with a ported (1.5") intake on the shelf.........no comparison (performance wise) to the larger side draft SUs.

[Sealik]

I dont run chokes on my SUs. They were half a turn rich in the winter. 28 degrees outside, and I could start my car in 1 revolution of the motor, and it would idle, though that idle was 450rpm, it would start and idle fine. Warm idle was 700rpm though so I couldnt have been too far off. I learned I could time cranking the motor over while pressing the gas pedal. It seemed as if there was a sweet spot where the motor fired instantly.

During the summer say April ish, I leaned out the carbs. They never required chokes.

Even after I had pulled my motor, and then reinstalled it 1.5 months later, it started first try.

I once changed my fuel filter in Napas parking lot. The car ran for 10 minutes with me blipping the throttle before it even pulled any fuel into the filter.

My guess is you're running really rich at idle....thus the start up in cold temps, or after sitting for extended periods
That said I'm not sure how cold it gets in you locale
All relative..... outside temp and how the carbs are 'set up'

Have a wibeband to confirm ratios????

[wayno]

[quote="Sealik"]Wayno....I can see you dropped the front SU mixture screw(seat) a tad more....relative to the rear one
This tells me your bushing and or throttle shaft is NFG.....<....leaking air.

I can't really get the back one lean enough anymore, it's wore out and almost not serviceable, the front one is fine, it adjusts properly and the spark plug color confirms it, the back one is always rich now.
I bought these carbs from Nissan back in 1995 when they had a clearance sale, $200.00 each, what a deal, and now 18 years of daily driving later, they need rebuilt, but the back one is not closed yet, almost, but not yet, it runs great the way it is right now, but I see a carb rebuild in the next year or so, it has been slowly getting worse, back plugs are always black now.
It likely needs re-jetted anyway, LZ23.

[Laecaon]

Hovers around mid 30s degrees farenheit in the mornings, though I had no problem starting the car on a few 20 degree days.

The only difference between my summer and winter tune, is half a turn on the nuts. Plugs are tan in the summer. I dont bother calculating my MPGs, but its better than my weber which did alright.

700rpm warm idle in the winter unchoked is the goal right? It just so happens my engine will idle at 450 when cold unchoked... I havent touched my distributor timing since I installed it back in my weber days. That got 28.8mpg once on a pure HWY tank averaging 65+mph.

The only thing I would say, is I am not running super rich. Plugs just are not black enough. My friend has a weber on his truck, you can see black smoke out the tail pipe. His plugs are BLACK when you kill the motor under heavy acceleration.

[datmo]

These carbs have chokes on them for a reason, and it's not for looks, as said above, these do not have any type of accelerator pump, you cannot pump the pedal and expect it to start as no gas is pumped into the intake, you really do need a choke cable for dual SUs, I use mine year round, hot or cold outside when starting it for the first time that day, otherwise it will turn over for extended periods of time before it might try to start, it should start within 3 seconds with a choke, not 10 seconds or more.
I even use the choke when it sits for 7 hours(time it takes to do a job), mine will not start cold, but I try not to run it rich either, when I pull my spark plugs, I want to see a slight white/yellow color, not black(rich), if I see black, I lean out that carb even more, that is why mine are not even close to the same now, the back carb runs rich.

As I said before, you should use the weber you have, but you cannot tune a weber like you tune SUs, webers are made different, for the most part, either they work great, or they don't run good at all, I personally don't like down draft carbs, but that's just me.

I completely see your side of it and on my current weber, I haven't been using a choke.
And it never gets anything under 40 here.
It's usually most always hot.

Hs2? Damn... Hs4 are the 1.5" ones, hs2 is 1/4. I did say hs2, the bolt holes and vents will line up but the center would have to be made a little bigger. The British carb sizes are funky :/ if the haven't shipped you can probably change the order but if they have they will still work

It's fine. I can prob widen the hole if it isn't good enough. and sadly, they're already shipped.
Plus, these almost look exact to taterhead.

Hovers around mid 30s degrees farenheit in the mornings, though I had no problem starting the car on a few 20 degree days.

The only difference between my summer and winter tune, is half a turn on the nuts. Plugs are tan in the summer. I dont bother calculating my MPGs, but its better than my weber which did alright.

700rpm warm idle in the winter unchoked is the goal right? It just so happens my engine will idle at 450 when cold unchoked... I havent touched my distributor timing since I installed it back in my weber days. That got 28.8mpg once on a pure HWY tank averaging 65+mph.

The only thing I would say, is I am not running super rich. Plugs just are not black enough. My friend has a weber on his truck, you can see black smoke out the tail pipe. His plugs are BLACK when you kill the motor under heavy acceleration.

If that's even going towards 20 degree weather, I'll be more than safe without a choke.
I won't be doing this completely alone.
My somewhat uncle will tune and teach me so that I can learn and i will be tuning my current weber to learn off of.
He'll instruct me and all.

Then I can try doing the duals as well as with his instruction because I'm sure that's a different story.

[datmo]

So i used that guide and I got my weber to idle by itself.
Felt pretty damn awesome.

[datmo]

So i got the filters and the carbs.
Problem,
When i put these filters on, the holes dont align but I can just drill new holes for that because they're off by a couple mm.

but more importantly.... the filter hits this thing and won't fit....






any ideas?

[Laecaon]

Commented on the other thread...

[datmo]

Thanks.
is this suppose to remain open like this?
Where does this go?



And there's a line on the side of the carbs that I'm not sure what is going to?

I'll get pics of it soon.

[Converted_to_datsun]

I pm'd you back. And the one in the was if where the fuel line goes into the float bowls. The one streight up is a overflow vent

[Converted_to_datsun]

Oh and the line on the side is a coolant line, there should be one in the same place on your stock manifold

[datmo]

I pm'd you back. And the one in the was if where the fuel line goes into the float bowls. The one streight up is a overflow vent

I'll see where the coolant goes to and figure that on my own.
Does the overflow get covered or go to anything?

[Converted_to_datsun]

I just put fuel lines on my overflows and directed them down. Some people run them back to the firewall and down. Basically it's preference

[datmo]

I just put fuel lines on my overflows and directed them down. Some people run them back to the firewall and down. Basically it's preference

So you let it run to the ground?
isn't that a waste of gas in a sense?

[flatcat19]

Gas needs to go somewhere.

Why wouldn't one hook those as a return line?
Is there a downside to using that a a return?

[Converted_to_datsun]

A return is for excess pressure, those vents are in case of overflow. Wouldn't work properly

[Laecaon]

It will mess up the carbs if connected to return.

it won't leak fluid unless something is wrong like a sunk float.

my SUs actually have a return port, but most do not.