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Zenith Stromberg Carburetor Vacuum Lines Schematic  Rate Topic 
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 Posted: 03-30-2005 10:51 pm
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Mark Rosenbaum
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A question came up elsewhere about how the vacuum lines work together on an engine with Strombergs.  The shop manual doesn't really show this, so I created a simple sketch.

Attachment: JH Vacuum Lines.gif (Downloaded 289 times)

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 Posted: 10-18-2013 10:29 pm
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pjg55
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Hi Mark,
Thanks for creating this schematic.

My question is what are the consequences of simply plugging off all these vacuum lines at the carb ? I have already converted the distributor to a non-vacuum assisted version and removed the carbon canister.

It would seem these are purely for emissions purposes and could be eliminated.

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 Posted: 10-18-2013 11:39 pm
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Jensen Healey
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I'm sorry to inform you that Mark Rosenbaum has passed away.

I don't know how removing all the vacuum lines would affect the performance of the engine.

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 Posted: 10-19-2013 01:26 pm
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Brett Gibson JH5 20497
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I have removed most of the vacuum lines and plugged them off leaving only the inlet manifold to the brake booster, plus I blank off the by-pass valve on the side of the carbs and adjust the temperature compensator so that it does not move and seals that chamber as well. Having done that and driven the car thousands of miles and done the same for a few other cars all I can say is it works for me.

Brett

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 Posted: 10-22-2013 11:37 pm
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pjg55
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Thanks for the info Brett. That is what I was looking for.

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 Posted: 12-15-2017 12:08 pm
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chrisl
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I have removed most of the vacuum lines and plugged them off leaving only the inlet manifold to the brake booster, plus I blank off the by-pass valve on the side of the carbs and adjust the temperature compensator so that it does not move and seals that chamber as well. Having done that and driven the car thousands of miles and done the same for a few other cars all I can say is it works for me

Hi Brett

I've acquired a set of Strombergs and am refurbishing them to fit on my GT. It currently has Dellortos on it and runs fine other than the stutter on flooring it but I think the Strombergs will make for smoother running.

Anyway, a lot of the pipework on the Strombergs is missing so I am working through what goes where. The shop manual is no help; and I see from your post above a lot of the vacuum lines aren't really necessary anyway.

I think I've got a good idea of what goes where but it would be good to confirm. Do you have a picture handy that shows which ones you've capped?

Did you also ditch the carbon canister? It wasn't fitted to RHD cars as far as I can tell.

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 Posted: 12-16-2017 06:49 am
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answerman
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Hi Chris: if this helps, I went through the removal of most of the vacuum lines when I was sorting out some running issues a couple of years ago (turned out to be distributor related). Still, I agree that most of the lines are unnecessary.

I removed the vacuum switch since it wouldn't be doing anything anyway, and also removed the vacuum retard line to the distributor (I ended up installing a different distributor that didn't have the retard).


Here's a "before" and "after" diagram (the "before" diagram is actually Mark's).

Before:





And after:




The original post with context is here: http://www.jensenhealey.com/forums/view_topic.php?id=1798&forum_id=15&page=6 (starts around post 107)

Last edited on 12-16-2017 06:55 am by answerman

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 Posted: 12-16-2017 11:39 am
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chrisl
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Brilliant; that answers the question.

These Strombergs have more holes than a block of Swiss cheese, plugging them saves a lot of messing around. I'm all for originality but...

Thanks a heap

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 Posted: 12-16-2017 06:21 pm
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Esprit2
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chrisl wrote:
I've acquired a set of Strombergs and am refurbishing them to fit on my GT. It currently has Dellortos on it and runs fine other than the stutter on flooring it but IIt's interesting to see how different people view and/or fix the same problems. I have 3 907 engines, and fixed all the carb issues by converting to Dellortos.

If your Dellortos have an off-idle hesitation, or don't otherwise run smoothly, then they are not properly set-up and tuned. If the Strombergs aren't set-up & tuned any better, then they will give you problems as well.

... a lot of the pipework on the Strombergs is missing so I am working through what goes where. The shop manual is no help; and I see from your post above a lot of the vacuum lines aren't really necessary anyway.
As far as removing vacuum lines goes, follow Answerman's simplified schematic. However, it's also important to defeat the devices those lines feed, rather than just disconnecting the hoses & plugging the ports.

The Bypass Valves allow intake flow to continue around the closed throttle butterflies during closed-throttle over-run. The strong manifold vacuum that would otherwise result would produce a strong spike in oxides of nitrogen. The Bypass Valves prevent that.

The Vacuum Switch (aka Vacuum Delay Valve) controls how long the Bypass Valves stay open after the throttles close. The Delay Valve and two Bypass Valves are all part of the same function. If you delete one, delete them all.

In addition to disconnecting the hoses, also blank-off the Bypass Valves. Remove each valve, replace the gasket with one that is hand-cut and solid (no center holes and passages for vacuum), and re-install the valves. The 'solid' gasket blanks off the valve, making it little more than decorative.

Separate, and not vacuum related...
If the Thermal Compensator is suspect or not working, then don't bother fixing or replacing it. Simply adjust the plunger in all that way such that it can never unseat/ open the port. The Thermal Compensator is a 'seasonal' thing, providing a slightly richer mixture during the warm-up cylcle in cold weather. Most 907 powered cars get put in storage and aren't driven during 'real' Winter. If that's the case for you, then restoring the Thermal Compensator is a waste of effort.

Regards,
Tim Engel

Last edited on 12-18-2017 05:07 pm by Esprit2

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 Posted: 12-18-2017 03:41 pm
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Brett Gibson JH5 20497
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Chris, sorry for not getting back to sooner, I was out of touch for a bit, but I see you got the answers you need from the group. good luck.
Brett

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 Posted: 12-19-2017 07:54 pm
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answerman
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Glad the diagrams helped. Tim brings up a good point, which I didn't mention above but was referenced in the link to my original post at the bottom of the diagrams.

In addition to removing the vacuum switch, disconnecting the lines and capping the ports (by the way, the caps are shown in red in my diagram), I also did disable the temperature compensator as Tim mentioned. Additionally, I did remove the bypass valves and cut/install a full face gasket for each to ensure that they were truly disabled. I should have mentioned that above.

I have to say: this is the first time I've ever heard of someone removing their Dellortos and replacing them with Strombergs. Usually it's the other way around. I'd love to replace my Strombergs with Dellortos, but it just doesn't make financial sense for me for the way I drive the car. If in the future I end up with some disposable income that I just can't find a use for, a set of Dellortos would be high on the list (along with a stroker kit).

Last edited on 12-19-2017 07:58 pm by answerman

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 Posted: 12-20-2017 12:00 am
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chrisl
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I also have a J-H with Dellorto's that runs well. It needs a bit of a tune up as it's running a fraction rich but doesn't have the 'stutter' on progression.

My GT originally came with Strombergs but a previous owner put D's on it; it runs well and I've even (nearly) got the flooding/stutter sorted. I managed to pick up a set of Strombergs and an inlet manifold for not a lot of $$.

I like to play around with various setting etc to see what works. The thought was to use the J-H as a speedster and the GT as more of a cruiser. It will be interesting to compare the pair if/when I fit the Strombergs. If I don't like it the Dellortos will go back on.

The responses and advice from everyone is greatly appreciated, have a great Christmas and new year.

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