510 Su's

[Patcon]

On 3/21/2018 at 5:04 PM, Patcon said:

Ok...the carbs are on Cody's car. We have done some preliminary tuning. It's drive-able but not perfect yet. Seems pretty rich. I am only 3/4 turns down on the mixture nuts. I set the floats at 11mm plus like Blues document had. Also I am looking at Ramflo for filters but can't figure out which one is right. Does the H1, H2 or H4 fit the Datsun 38mm carb?????

anybody have anything on this????

Also I ended up going with the Triumph choke cables. They work great, but I had to shorten the jacket on the front cable. About half the cost of a set of roadster cables

Edited March 23, 2018 by Patcon

[NVZEE]

Ramflo isn’t as common here as the K&N tuna cans — this might do the trick http://www.thezstore.com/page/TZS/PROD/11-3010.

As for the vacuum source, the manifold will have one or two threaded ports on top of the runners you can use. Scrounge around for a threaded nipple that suits your hose size. What you’ll see done with the water line is to loop a section of heater hose long enough not to kink from one fitting to the other, kind of a pigtail. Don’t remember exactly but there may have been a factory hose that did this, once upon a time.

Edited March 23, 2018 by NVZEE

[Patcon]

7 hours ago, NVZEE said:

Ramflo isn’t as common here as the K&N tuna cans — this might do the trick http://www.thezstore.com/page/TZS/PROD/11-3010.

As for the vacuum source, the manifold will have one or two threaded ports on top of the runners you can use. Scrounge around for a threaded nipple that suits your hose size. What you’ll see done with the water line is to loop a section of heater hose long enough not to kink from one fitting to the other, kind of a pigtail. Don’t remember exactly but there may have been a factory hose that did this, once upon a time.

Yeah I have noticed ramflo's aren't as common but I like the look. I just don't know which style is correct for the 38mm carbs.

One of the problems with looping the hose is the hard line was too long to connect to manifold, so I cut it back before I replated it. So that tee is now gone. I guess the real question is do I need that flow out from under the thermostat into this line?

[240260280]

13 hours ago, Patcon said:

Also there were a number of water ports near the carbs. Best I could tell water flow was from the head into the manifold then towards the front. The port out of the thermostat housing and the 90 degree tee out of the straight line were tied together with a hose and the other went to the old carb. For now I plugged the thermostat hole and connected the su manifolds to the line that runs around the front of the head. Should I do it differently?

 

Heating manifold is a good thing:

 

1. Condensed fuel evaporates faster.

2. Less condensed fuel on colder days when engine warms up.

 

 

[240260280]

13 hours ago, Patcon said:

I have another question, there is no port for the vacuum advance. Can I use another port off the manifold? In other words, is there anything special about where that port exits the front carb. The is no booster on Cody's car so I could use that port for vacuum advance and still use the center port for the PCV valve...

 

Yes, 

 

1. Manifold vacuum port is high when idling.

2. Ported vacuum is high when off idle and when cruising.

 

Cars start easier with less advance (so that an early [advanced] explosion does not push the slow moving crank somewhat backwards when cranking at 200rpm).

Cars accelerate better just off idle with more advance.

Cars use less fuel at cruise with higher advance.

 

You need to find a ported vacuum advance source. Usually these are tapped near the throttle plate and come out to a small pipe.

 

 

 

[NVZEE]

18 minutes ago, 240260280 said:

Heating manifold is a good thing:

 

1. Condensed fuel evaporates faster.

2. Less condensed fuel on colder days when engine warms up.

 

 

It also might be necessary for best coolant circulation.

[Captain Obvious]

To further what Blue said about the vacuum source... The Z's all used a "ported" vacuum source, but I do not know what the 510 used. Since it's so similar in lots of ways to the Z, I would assume it wants a ported source as well, but I guess there's no guarantees.

Here's an old thread that discussed the differences and advantages, etc of the two:
http://www.classiczcars.com/topic/41935-ignition-timing-theory-port-source-vs-manifold-source/

As an aside... I Teed in a vacuum gauge to my Z and routed the line to the interior. I drove around for a while like that with the gauge attached. It did exactly what I expected:

Zero vacuum at idle.
Narrow peak of highest vacuum just off idle at light cruise. About 20 inches hg at the sweet spot pedal position at 4000 RPM.
Near zero vacuum at WOT.

[NVZEE]

Borrowing a photo from another thread, you can see the distributor vacuum line going from the fitting on the manifold runner to the left of the front carb. Some manifolds have one threaded hole in each pair of runners, others only have one on the rear pair. From the nipple fitting in this installation, the hose is routed under the front carb and over to the distributor. You can also see part of the arched hose under the plug wires that connects the thermostat housing to the manifold.

Ignore the yellow circles from the original post here:  http://www.classiczcars.com/forums/topic/45006-twin-flat-top-su-problems/

 

 

[NVZEE]

The option for vacuum is to take it from the nipple at the base of the front carb, where the yellow cap is in this photo. Considering the other comments, this would seem preferable.

Edited March 23, 2018 by NVZEE

[Patcon]

5 hours ago, NVZEE said:

The option for vacuum is to take it from the nipple at the base of the front carb, where the yellow cap is in this photo. Considering the other comments, this would seem preferable.

That's on the underside of the carb. I will have to look again. I expected it to be on top like the 46mm carbs

[Patcon]

11 hours ago, 240260280 said:

 

Yes, 

 

1. Manifold vacuum port is high when idling.

2. Ported vacuum is high when off idle and when cruising.

 

Cars start easier with less advance (so that an early [advanced] explosion does not push the slow moving crank somewhat backwards when cranking at 200rpm).

Cars accelerate better just off idle with more advance.

Cars use less fuel at cruise with higher advance.

 

You need to find a ported vacuum advance source. Usually these are tapped near the throttle plate and come out to a small pipe.

 

 

 

So I do have the manifolds heating but I have the port coming out from under the thermostat blocked off

[Captain Obvious]

That sure looks like a ported vacuum source to me. My assumption is that the little brass dot above the "F" is the plug they pressed in after they drilled into the carb throat.

33 minutes ago, Patcon said:

That's on the underside of the carb. I will have to look again. I expected it to be on top like the 46mm carbs

It's actually convenient to be on the bottom, right? Shorter line over to the distributor.