Webers or Strombergs

[dodo_z]

If you use the Weber head, you could easily use DCOE style throttle bodies for fuel injection. Then you have optimum fuel efficency while getting most power from the engine - never running fat or lean. It is not historical correct, but some TUEV engineer will acept it as a concession to our environment

But Iif you like to switch to a stromberg head, which is cheaper than a weber head, I 'd like to buy your weber head

dietmar

[Esprit2]

I have been waiting patiently for replacement temperature compensator strips for my strombergs since January.

The Stromberg's Temperature Compensator isn't a "must have".

The compensator reacts to engine bay ambient temperatures, and adjusts the mixture slightly with seasonal changes. Without the compensator, it may be necessary to make a minor adjustment between Summer and Winter driving, but how many Elan's get driven in Winter weather. Not just Winter on the calendar, but true, cold weather. not many.

Simply over-adjust the compensator such that it will never open under any conditions. Then adjust the mixture for best operation during the Summer, and don't worry about what the compenstor would be doing if you were during the Winter.

Same with the Throttle Bypass Valve... just blank it off by installing a hand-cut, solid gasket. The engine will run more happily without it.

Regards,
Tim Engel

[69S4]

Hi Juergen

I have been waiting patiently for replacement temperature compensator strips for my strombergs since January. Gower and Lee (Watford uk) recently told me that some firm (that I can't remember the name of) are remanufacturing these and other stromberg bits. This is due to a build up of demand from jaguar, Lotus and other owners. They are due this month.

I thought you might find this helpful as these strips have to be replaced every so many k miles.

Jim

Are they producing the whole unit or just the bimetallic strips? I'm not quite sure why you'd have to replace the strips as a service item - it's not as if the "bimetallicness" wears out and they are adjustable. The question that's been kicked around here and on various other Stromberg using car sites has been what to adjust them to. I set mine up to "TR6 spec" - opening at around 46C and fully open at around 60C, ( http://www.buckeyetriumphs.org/technical/Carbs/CarbsI/CarbsI.htm) and they seem to do very little (or at least I can't distinguish between before and after). Maybe that's how it's supposed to be.

The Strombergs on my S4 came with the bypass valve area blanked off from new. As I understand it only the US versions that had the things fitted.

[Esprit2]

The Temperature Compensator's effect is subtle when operating correctly, and it was only used on the emissions version of the carb, the CD-2SE. The goal was to run a lean mixture for emissions. But there is a very narrow margin between optimally lean for emissions and too lean for the engine to run well.

The mixture needs to be slightly richer for an engine to run equally well in colder weather. If the mixture was set emissions-lean during the Summer, then it would be too lean for the engine to run well in the Winter. If the mixture was set during the Winter, then the it would not pass emissions tests in the Summer... or when fully up to operating temperature.

Vintage, pre-ECU emissions-lean was on the ragged edge of poor running at it's best, and any seasonal variation that pushed it leaner was felt when the engine's running went from poor to worse. The Temperature Compensator provided the "small" enrichment to keep the emissions-lean mixture in the merely poor but clean running range without drifting off to worse.

The manufacturers were required to produce a solution that met emissions standards all year around without relying on the owners' maintenance dilligence and good will, and the Temperature Compensator did that.

The compensators were specifically tuned for each engine application, and the settings were not published. If you're just using some other engine's compensator or settings, then you're not really preserving your engine's emissions set-up anyway and you may as well just set it to plugged, another wrong setting. The operational difference is subtle anyway, and the difference between correct, wrong and plugged is not big.

Non-emissions Strombergs (CD, CDS, CD-2S) all got along very well without the Temperature Compensator and the engines were happier without them... happier but not emissions cleaner. If you have removed any of the engine's emissions equipment, hotrodded it, advanced the ignition timing, changed the needles & jets to improve it's performance, then you've already thrown out enough emissions originality to totally mask the subtle benefit of a working Temperature Compensator. At that point, you're kidding yourself if you're thinking you're doing anything good or necessary by preserving the compensators.

If you don't drive your Lotus during the Winter, then the Temperature Compensators have little real value.

Instead, simply screw the adjuster in so far that the cylindrical plug will never back out of the port under any operating conditions. Even add a little sealant. Then adjust the fuel mixture for whatever best-running conditions you are targeting for the rest of the engine.

If you are running a full emissions-spec engine, then the compensators need to be to the correct original specification for that engine. Something from a Triumph TR6/ TR250 or Volvo isn't going to get you there.

Regards,
Tim Engel

[Esprit2]

The Strombergs on my S4 came with the bypass valve area blanked off from new. As I understand it only the US versions that had the things fitted.

Hmmm... the Parts Manual doesn't indicate two configurations. But regardless...

The Throttle Bypass Valve reduced the vacuum level on over-run in order to reduce the resulting emissions spike. It kept the rpm up for a few seconds after the throttle was released (which seem kinda funky); but other than that, it has no significant impact on how the engine runs.

If it stuck closed, you would never notice.

If it stuck open, it could destroy the engine's ability to idle down. If the engine suddenly develops a very high idle and won't adjust down, the first thing to suspect is a bad Throttle Bypass Valve.

Removing it and/or blanking it off has no negative imact on how the engine runs (other than it's obvious emissions function), but does significantly improve the throttle response.

If you're trying to maintain a fully emissions original engine, then the Throttle Bypass Valve is needed.

If you've modified the engine, then it makes little sense to put money into maintaining or repairing the valve. Just hand-cut a solid gasket for it to blank it off.

Regards,
Tim Engel

[69S4]

Thanks for all of that Tim. Having had the TC's jammed shut for decades I've got a good feel for how the engine responds without them but having just put in a fair bit of time and effort overhauling the carbs it was inevitable that I'd turn my attention to them and try return them to the state that Mr Stromberg intended. It did surprise me to an extent that Elan usage calibration data for them didn't seem to be freely available, even from the businesses like Burlen who are now the keepers of the flame. It may have been a case of "no user serviceable parts inside" back in the 60's but it's hardly sensitive information these days. Maybe we've gone straight from "not telling" to "can't remember" without the intervening "what does it matter".

You're right that calibrating them using another car's data isn't a sensible approach but if the effect on the way the car drives is so subtle as to unnoticeable then we're into "how many angels are dancing on the head of this pin" territory. I suppose it's a character flaw that makes me prefer to have it working and wrong rather than not working and wrong - especially when there doesn't seem to be a downside. Compared to the other lash up compromises that you have to make to keep an Elan on the road, dangling the TC's into tubs of warm water seems like a harmless pastime. If nothing else, my wife is using it as a reason to check vacancies in the local care homes

[Esprit2]

> It did surprise me to an extent that Elan usage calibration data
> for them didn't seem to be freely available (Snip)...

> I suppose it's a character flaw that makes me prefer to have it working
> and wrong rather than not working and wrong - especially when there
> doesn't seem to be a downside.

Stuart,

The calibration data is not just not freely available, but intentionally withheld. They didn't want anyone messing around in there, and not publishing the settings was their version of anti-tamper screws.

As far as "fixing" the Thermal Compensators... have at it. We own these cars because we want to, not because we need transportation. Do whatever gives you pleasure with it. One last comment, and I'll leave you to it.

If the Thermal Compensator is installed in working condition, then it can one day fail in a way that may cause the engine to run poorly. The impact of the T-C's normal operating range may be small, but the potential impact of it's failure can be large. Of course, then you will notice it.

If it's jammed closed, it can't work, but it can't fail either.

I fix vintage mechanical film cameras just because I like messing with small mechanisms. In this digital age, most of my completed projects just go on a shelf without ever seeing another roll of film after they've been repaired. I can't throw stones at someone who wishes to fix the Thermal Compensators.


Regards,
Tim Engel

[FOX5D]

Hi Stuart

They are producing the whole unit and I received a pair in the post this morning. I am now handing them over to Phil Webb at the South West Lotus Centre at Lifton in Devon to complete the overhaul of my carbs. I will also copy him the opinions expressed in this thread for good measure.

Jim

[FOX5D]

hI everyone

I just wanted others to know that I have just had my stromberg elan back from SWLotus centre Devon, after fitting the new temperature compensator strips. She drives beautifully, ticks over at 800 and for the first time doesn't run on. Starting is very consistent, with choke when cold and foot down when hot. I definitely prefer strombergs to webers.

Jim

[elanbaby]

Hi all,
after 3 weeks holiday in Devon and Cornwall I?m back at the workbench.
I visited Miles Wilkins and although having been "warned" I found him and his partner Ian very friendly and helpful.

Anyway, he didn?t try to persuade me into Strombergs, there are pros and cons to both carb types as to everything in life.

After inspecting the carbs I have at hand I came to the conclusion that my webers are in better condition as my strombergs. Both heads require some work, valve guides and seat recut mainly. I?ll take the Weber route from now on.

A question about the valve seats came up, but I?m going to start a new thread on that topic now...

Juergen