Lotus Elan

Can 5ne adapter plate be removed from federal zenith strombg

PostPost by: sabbot » Mon May 18, 2020 5:29 am

Hi all,
I’m wondering if anybody has had experience of removing the adapter plate that is fitted between the Zenith Sromberg carbs and the inlet manifold on federal twincams. My car came with it in a box but it has never been fitted. I got the car running (roughly) for the first time today without it and have had to subsequently remove the carbs for cleaning. The adapter plate has the federal emissions tubes blanked off and as far as I can see the only benefit to it is that it has an integral balance tube built into it. Is the balance tube needed for Strombergs? .
I’m contemplating leaving it out when I put the carbs back on but would be interested in opinions to it’s utility if the emissions tubes are blanked off. The inlet manifold is tapped for vacuum so I don’t need to use the vacuum takeoffs on the adapter plate if I don’t want to.
Thanks
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PostPost by: oldelanman » Mon May 18, 2020 6:48 am

In my opinion you need to retain it or maybe replace it with the UK (non-emission) balance tube system, if you can source it.
The combined effect of the firing order and the siamesed inlet runners means that a balance tube is required to even out the inlet depression fluctuations and achieve smooth running, particularly at idle. Also the large O ring on the adaptor plate together with the thackery washers under the nuts provide a flexible mounting which is supposed to prevent fuel frothing in the carbs ..... bolting the carbs directly to the inlets may cause problems.

There have been several discussion on this in the past, try searching "secondary throttles"
Here's an example.....

viewtopic.php?f=40&t=26914
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PostPost by: Gordon Sauer » Mon May 18, 2020 4:24 pm

Just from a practical standpoint, when I first got my plus 2S 130 in ‘89, it did not have the intermediary section But did have a balance pipe between the two carburetors,and the Strombergs were bolted right to the manifold and I drove it around for like a year and a half like that with no problems but in the end I decided to go “original“ and put it all back to what it was to look like. Gordon Sauer
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PostPost by: sabbot » Tue May 19, 2020 12:32 am

Thanks all,
The replies and link are very helpful; I’m going to add the plate back.
Also please excuse the typos in the original message.

Stewart
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PostPost by: RogerFrench » Tue May 19, 2020 6:12 pm

Gordon Sauer wrote:Just from a practical standpoint, when I first got my plus 2S 130 in ‘89, it did not have the intermediary section But did have a balance pipe between the two carburetors,and the Strombergs were bolted right to the manifold and I drove it around for like a year and a half like that with no problems but in the end I decided to go “original“ and put it all back to what it was to look like. Gordon Sauer

I'm curious to know how a balance pipe was installed without the adapters or secondary throttle body.
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PostPost by: Esprit2 » Tue May 19, 2020 7:14 pm

Stewart,
The Federal emissions Zenith-Strombergs were jetted lean enough that the fuel didn't ignite as readily, or burn as completely. In order to facilitate the lean mixture, Lotus added the cross-over pipes to the exhaust manifold and back. The mixture was heated, making it more volatile so that it ignited more quickly and burned more thoroughly.

If you're going to retain the stock, Federal Z-S set-up (really ??), then keep the cross-over pipes. And the cross-over pipes require the secondary throttle adaptor, so keep it as well.

But if you're going to install richer needles in the carbs and re-tune for power and good running instead of low emissions (ie, the Euro needles & set-up), then either...

1) Block-off the cross-over pipes and delete the secondary butterflies. That will deactivate all that, but the engine bay will still look original. Or...

2) Delete the cross-over pipes, replace the secondary throttle adaptor manifold with the Euro adaptor maniold without all that mess, or find one of the aftermarket billet clones of the Euro part that have been made in the past.

But, regardless of your choice above, the high cross-over pipe is a necessity, and should not be deleted. Do not simply eliminate the adaptor manifold/ cross-over pipe, and mount the Z-S carbs directly to the intake manifold. Doing that will result in un-even mixture being delivered to the cylinders, and it can not be tuned-out/ fixed/ eliminated. The cross-over pipe was taking care of that, (well, 'most' of that) and eliminating the pipe means you live with the mixture problem.

Extend the 1-3-4-2 firing order, and it becomes 2-1, 3-4, 2-1, 3-4, front carb for two, rear carb for two, front carb for two...

Each carb works for two, rests for two. But fuel is heavier than air and has more inertia, so it responds more slowly to the start of flow. So coming out of a rest period, the first cylinder gets a leaner mixture because the heavy fuel is slow to get moving, and the second cylinder gets a richer mixture because the heavy fuel has caught up. So it's leaner-richer, leaner-richer, leaner-richer. That's simply a function of that 'Y'-siamesed intake manifold combined with the 1-3-4-2 firing order. You can't make it go away simply by tuning.

If you adjust the mixture so the first cylinder has okay mixture, then it becomes okay-too rich, okay, too rich...

If you adjust the mixture so the second cylinder is okay, then it's too lean-okay, too lean-okay. Even if you compromise such that neither cylinder is correct, the first will still be leaner than the second. Two wrongs don't make a right.

So, in one form or another, it's leaner-richer, leaner-richer, and the balance tube helps to mitigate most of the problem. The balance tube is "tuned", and it's diameter and length are important. Also, it's location, above or below the intake runners is important. The stock 'high' balance tube is very good... call it "right". Don't run without the balance tube. But if you buy an aftermarket billet adaptor manifold, choose one that has a high balance tube that mimics the Lotus dimensions.

Regards,
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PostPost by: Gordon Sauer » Wed May 20, 2020 1:59 am

A picture of mine follows and I have the intermediary section with the throttle plates cut out in a pattern that leaves just the sides of the plate available so I don’t have to deal with a leaking spindle or epoxied spindle holes, and the width of the throttle plate is retained in the opening with the set screws still in it, hoping to not have disrupted airflow; and the balance hose is the one you see in the front (not the wrapped up one which is the fuel line T) that goes to the front side (right as viewed). That balance hose was on the carbs when I got it at the point they were bolted to the manifold and I kept it. These are the ZS with the temperature compensator valve, adjustable needle and a manual choke of my 1973+2S/130.Gordon Sauer
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