Lotus Elan

vacuum retard port with stromberg carbs

PostPost by: chickenstock10k » Tue Mar 12, 2019 8:48 pm

Does anyone have a photo of where the vacuum retard line runs from the distributor on a federal dizzy and stromberg carbs? The shop manual isn't very clear and I have searched in the archives without much luck!
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PostPost by: 1owner69Elan » Tue Mar 12, 2019 9:05 pm

Hope this helps:

img_1533.jpg and
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PostPost by: tedtaylor » Wed Mar 13, 2019 3:07 am

I know nothing of a "manifold depression valve" on my Federal Sprint. My vacuum tubes all connect at the blue charcoal canister in the nose of the car.
here's an excellent diagram showing the routing.
http://rdent.com/manuals/elan/fuel_system/la.htm
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PostPost by: chickenstock10k » Wed Mar 13, 2019 3:18 am

For clarity, and for folks that stumble onto this later, I?m working on a Plus 2 and will take photos of the relevant parts in the diagram over the weekend.
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PostPost by: 1owner69Elan » Wed Mar 13, 2019 6:04 am

Ted: I think what you are showing is the evaporative recapture system present in the later Sprint (your car). These are not vacuum lines, I don?t believe.

The vacuum retard system as shown in the diagram I posted above was installed on earlier S4 Federal cars. This includes vacuum lines running from the intake manifold to carbs and distributor with a valve activated by the throttle. This was the original setup on my 69 Federal S4 as delivered to me at the factory. This is what the original poster appeared to be asking about. But he can clarify.

I have further documentation on the Federal emissions controls including the vacuum retard if anyone is interested. I happen to have this directly from the original designer of the system for Lotus. Not sure if it was ever widely published. May be of Lotus historical value.

PS: All of this is now moot for me as I have a non smogged Weber setup now.
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PostPost by: Evante » Wed Mar 13, 2019 12:53 pm

I would like a copy of the emissions vacuum control.

Thanks,

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PostPost by: chickenstock10k » Wed Mar 13, 2019 1:39 pm

One owner, you hit the nail on the head.

I am doing a little tuning to try and solve a, very light, rough idle problem. I noticed that the distributor vacuum wasn?t hooked up and it sent me down a rabbit hole to understand the system and think about whether or not I want it hooked up. Given all the variation of these systems over time the shop manual doesn?t always do a great job with the specific details!
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PostPost by: chickenstock10k » Wed Mar 13, 2019 1:46 pm

I wish I could move this to the engine section, where I had intended to post it.

Here is an interesting photo that I just found in the archives: http://images.lotuselan.net/lel/24008/0/Throttle.jpg

It isn't exactly what I had expected. It looks like the distributor is connected to the manifold depression valve on the carb and then everything else vents to the case.
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PostPost by: JohnCh » Wed Mar 13, 2019 2:29 pm

The photo in the archives appears to be a marked up screenshot from the workshop manual. The functional description from that section reads: "As well as the modified induction system a special distributor is necessary. This is equipped with a vacuum retard capsule arranged to operate only when the throttles are closed; that is on idle and over-run. This is actuated by a valve attached to the rear carburetter which, when depressed by the throttle lever, connects the distributor to the manifold depression."

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PostPost by: USA64 » Wed Mar 13, 2019 2:51 pm

I have the valve. It is a simple plunger on a spring which opens/closes the line. Apparently the carbs are not "switched" by the valve and so subject to vacuum variation. No one sells the valve to my knowledge. I'd like another myself.
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PostPost by: 1owner69Elan » Wed Mar 13, 2019 8:24 pm

The Workshop Manual that I picked up at Hethel with my car in July 1969 had no information on the Federal Emissions system. Thereafter I acquired a copy of a supplement "S" (19 pages) as shown below. Apparently later versions of the Workshop Manual did include information on the Emissions controls - perhaps incorporating this Supplement "S"? I don't know if this included all the 19 pages of the supplement or not.

img_1534.jpg and


If anyone needs it I can scan the supplement "S" and post it.

I should note that most Federal cars have long since subverted the Emission controls:

1. Blocking (and removing) the crossover pipes
2. Removing or fixed opening the secondary throttle butterflies
3. Ignoring the vacuum retard, disconnected

I think I left the vacuum connections on the CDSE carbs not thinking they did much (only work at idle and overrun).

The fellow (Gary O'Neill) that designed and tested the system for Lotus always felt it did not overtly affect the car's performance because it reverted to a non-emissions version at WOT. Nevertheless, IMHO the car did feel sluggish in normal driving compared to the non-emissions version with a slow throttle response until significantly depressed.

The emissions controls in my state California have become obsolete as the Elan is exempt from smog testing. However, if you bring an Elan into the state for the first time to be registered apparently they look for the placard that indicates compliance at the time of manufacture (even though it will never be tested).
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PostPost by: chickenstock10k » Wed Mar 13, 2019 8:49 pm

1owner, I'd appreciate it if you could scan the supplement. My manual doesn't have anything that covers the federal emissions system.

The other components I am trying to get a little smarter on are the throttle bypass valves. I am getting a little popping on overrun (hard deceleration at lower rpm) and am wondering if my TBVs are on their last legs. As stuff comes up I try not to shoot from the hip but that can be hard if you don't know how it is all supposed to work!
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PostPost by: tfb0001 » Wed Mar 13, 2019 11:17 pm

I fought with my 69 S4 distributor for years before I finally replaced it with the Pertronix centrifical advance unit and I now wish I had done it years ago. The acceleration is so much better and the torque is so broad on hill climbs that I would recommend it to everyone with federal Strombergs. Something you learn after 40 years of Lotus ownership!
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PostPost by: 1owner69Elan » Wed Mar 13, 2019 11:33 pm

The Federal Stromberg Supplement S to the Lotus Workshop Manual is too big to attach as a file to this post. PM me your email and I will send to you.

Regarding the change to a different distributor. Undoubtedly the Pertronix distributor provides much more centrifugal advance than the Federal distributor. As shown on page 16 of the supplement the advance supplied is only 7 degrees.
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PostPost by: JohnCh » Thu Mar 14, 2019 2:21 pm

The Federal advance curve really impacts drivability. I just switched from the stock Federal curve advanced by 3 deg to the non-Federal curve retarded by 2 deg to compensate for local fuel. Throttle response is significantly improved and much closer to what you feel with Webers.

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