Lotus Elan

Strombergs not returning to idle

PostPost by: collins_dan » Sat Oct 16, 2010 3:58 pm

I rebuilt the strombergs this summer. They had many issues, so all seals, orings, thackery washers and needles were replaced with new adjustable needles. The car's performance has been transformed, but am having an annoying issue. They do not want to return to idle, which becomes more pronounced as temperature rises. In addition to all the replacement parts, the temp compensators were tightened down completely, throttle bypass valves removed and blanked off and the fuel lines are covered by temp resistant insulation. A couple of interesting things: 1) if idle is stuck at 1500-2000 and engine is turned off, then turned back on, the idle is at 800-1200. 2) if the engine is running and the lever arm is pushed slightly, it will hang up and leave the car idling at 1500-2000, but this will not happen if the engine is off. 3) giving the throttle a blip while driving seemed to return the idle to normal if stuck, but seems to not be very effective anymore. I didn't find anything helpful in the archives, hence the post. I appreciate any advice. Thanks. Dan
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PostPost by: Galwaylotus » Sat Oct 16, 2010 5:05 pm

When I had some work done on my S3, I had similar symptoms on its return. The mechanic had tried to be tidy and tywrapped the throttle cable down. As soon as I released it, the symptoms disappeared. May not have anythiing to do with your issue but it's a simple check! 8)
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PostPost by: Tonyw » Sun Oct 17, 2010 5:37 am

Galwaylotus,

Check the dashpots have the correct amount of oil and the correct viscosity as they can hang up sometimes if wrong. Also just check and make sure that the air pistons move freely up and down you will need to take the air box of to check this of course.

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PostPost by: elan_fan » Sun Oct 17, 2010 8:06 am

Do you have the throttle return spring on? The Stroms both have return springs but you should also have the extension spring going from the airbox to the throttle lever.

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PostPost by: collins_dan » Sun Oct 17, 2010 2:35 pm

Dash pots full, throttle cable free with spring attached. I'm wondering if the brass fitting around the spindle is too tight. They were a challenge to fit in the first place and there seems to be a squeak when rotating with engine off. It would explain why as the engine temp increases, they become restrictive. Short of pulling everything apart, any options for lubricating? Thanks. Dan
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PostPost by: 69S4 » Mon Oct 18, 2010 8:33 am

Sounds like yours are just that bit tighter than mine. I've been getting a slight bit of this as well since the carbs were rebuilt. The seals do seem to have a lot tighter grip on the spindles than the old ones but at least do have the side effect of being airtight :lol: .

I found that the return spring was just about ok on each carb individually but when you linked the two via the flexible spring connector there was a slight amount of misalignment caused by how each carb was bolted on. The spring connector would take this up but it increased the drag on the spindles.
Careful tweaking of the three nuts on each carb minimised it and the seals did/do loosen up a bit with time but it still drags slightly as it gets towards the shut position. I have considered a spring from the cable end to the airbox but haven't done it yet.
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PostPost by: leifanten » Mon Oct 18, 2010 1:30 pm

I have had the same issue as well. What I found to be the most influential factor is to make sure the screws that hold down the cover on the top of the carbs must be 100% evenly tight. The way to do that is to remove the airbox and feel the movement of the air piston whilst carfully tightening the screws in criss cross fashion. The reason is that the tolerances in the air piston and cylinder are extremely tight, and if the torque is not 100% even it can pinch the piston when it moves up and down. Typically exasperates when hot, since the metal expands.

I managed to get mine 90% good. I still have one of the carbs "fluttering" around 1500rpm on idle for a few seconds on some occasions in hot weather. It settles down if I partially engage and re-engage the clutch. I would love some advice on how to settle this final niggle, but it does not bother me anymore.
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PostPost by: Gray » Fri Oct 22, 2010 1:05 pm

Hi

I have had this problem with Strombergs even when they were relatively new, from memory (it was a long time ago) tightening the carb tops evenly as previously suggested made a lot of difference, but some carbs were still dificult.

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PostPost by: collins_dan » Fri Oct 22, 2010 2:41 pm

Thanks for all the suggestions. I will run through them all, many I have already tested, but can't hurt to run through again. I'll report back with the results.

Dan
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PostPost by: collins_dan » Mon Oct 25, 2010 1:50 am

I think it is the throttle spindle couplings. One seems to be quite twisted and allows the rear carb not to close all the way. Is it possible to remove and replace these in situ and not need to rebalance carbs? Thanks, Dan
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PostPost by: oldelanman » Mon Oct 25, 2010 4:37 pm

collins_dan wrote:I think it is the throttle spindle couplings. One seems to be quite twisted and allows the rear carb not to close all the way. Is it possible to remove and replace these in situ and not need to rebalance carbs? Thanks, Dan


Hi Dan,
If you are talking about the W couplings on the throttle spindles you can remove them without disturbing anything else - that's assuming that your federal carb set-up is the same as the european. I've just tried it on mine and it's just a matter of loosening both screws in each coupling then slide the rear one fully onto the rear carb throttle spindle you can then pull off the intermediate shaft and the front coupling in one piece.

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PostPost by: collins_dan » Mon Oct 25, 2010 5:36 pm

Thanks. Yours actually look in better shape than mine.
I'm really hoping this resolves the high idle. Minor problem, but major annoyance.
Dan
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PostPost by: bill308 » Mon Oct 25, 2010 10:23 pm

Dan,

You wrote, "I think it is the throttle spindle couplings. One seems to be quite twisted and allows the rear carb not to close all the way. Is it possible to remove and replace these in situ and not need to rebalance carbs? Thanks, Dan"

Air flow imbalance is a real possibility that can cause your symptoms. Although I usually use a bank of manometers to synchronize my Webers/Dellortos, I'm not sure they would work with the Strombergs as there is a balance tube in the manifold. I recommend you obtain an air flow meter like a Synchrometer and compare the front to rear carbs flow rates. This is probably the best way to synchronize Strombergs. A Unisynch is affects the flow too much an is not very accurate and a comparision of hiss using a tube is even worse as it is subjective and subject to placement.

The other thing to look at is the ignition advance. If it is not returning to a stable condition at idle, you will not have a steady idle. Check this with a timing light.

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PostPost by: collins_dan » Tue Oct 26, 2010 10:55 am

I will recheck sync and timing, how will I know if it is not stable? Dan
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PostPost by: Tonyw » Tue Oct 26, 2010 11:59 am

Dan,

You will know because you will not be able to get the same readings consistently.

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