Lotus Elan

Stromberg adapter plates

PostPost by: Pete M » Sun Jul 05, 2020 1:01 pm

I understand the theory behind mounting the stromberg carbs via the adapter plates to the intake manifold but have failed miserably in the attempt. Ray sent me new Thackery washers and Nylock nuts for the attempt but upon taking the car for a run the idle ran up to 2500 RPM. I sprayed a little carb cleaner on the joint and the idle settled down to about 1000 RPM which tells me I have an air leak. Does anyone have some tips or tricks for accomplishing an air tight fit?
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PostPost by: 69S4 » Sun Jul 05, 2020 3:16 pm

It's the O rings that are critical - both their condition and their location. My washers and nylocs go back many years but the O rings get changed every time the carbs come off. They swell with use so they don't fit 2nd time round - not for weeks anyway.

Strombergs are not as flexibly mounted as Webers and 'just about moves' is just about right. The manual mentions measuring the gap between the flange and the block and setting it 0.070" but that's too slack for my car, with hardly any pressure on the washers / nut and I get air leaks. Mine end up around 0.040".
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PostPost by: Pete M » Sun Jul 05, 2020 3:46 pm

Stuart,
Thanks for confirming my suspicions. I've tightened up the mounting nuts to about half of the factory recommendations re: the gap and started it in the garage. Idle is back to normal but I haven't taken it out on the road yet. Got my fingers crossed.
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PostPost by: oldelanman » Sun Jul 05, 2020 3:51 pm

It's also important to use the correct O rings for the job .. they are not a standard size .. and to tighten the nuts evenly in small increments to keep the joint faces parallel. I too have found that 0.040" is about right for the final gap. Don't forget the O rings on the ends of the balance tube (if you have the non-emission set-up that is) .. worth renewing those as well if you haven't done so recently.
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PostPost by: Pete M » Sun Jul 05, 2020 5:23 pm

Roger,

Thank you for your reply. I was coming to the conclusion that .035 might be the target, but thanks the most for mentioning the balance tube. Just got back from my test run and remembered I had left it off the rear carb.
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PostPost by: SENC » Sun Jul 05, 2020 8:17 pm

Pete M wrote:Roger,

Thank you for your reply. I was coming to the conclusion that .035 might be the target, but thanks the most for mentioning the balance tube. Just got back from my test run and remembered I had left it off the rear carb.


Your last comment has me confused - how can you leave the balance tube off one carb only? Or just the o-ring?
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PostPost by: Pete M » Sun Jul 05, 2020 9:58 pm

My balance tube just pushes onto the nipple coming out of the adapter plate. I'm confused by your mention of o-rings. I've snapped a photo but the file is too big to upload.
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PostPost by: SENC » Sun Jul 05, 2020 10:47 pm

Pete M wrote:My balance tube just pushes onto the nipple coming out of the adapter plate. I'm confused by your mention of o-rings. I've snapped a photo but the file is too big to upload.


We must be using the same term for different things. Here is a picture with 2 sets with balance tubes/pipes - the top has the upper balance tube, the one installed has the balance tube at the mid-level. There is a third type, the federal version that accommodates the emission control pipes. These non-federal balance tubes require o-rings where they seat into the manifold plates to preserve vacuum.

Inkedbalance tubes_LI.jpg and
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PostPost by: Pete M » Sun Jul 05, 2020 10:57 pm

That's a whole lot of carburetors. Mine is just a rubber tube.
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PostPost by: Evante » Sun Jul 05, 2020 11:27 pm

As previously posted, the o-rings need to be in good condition, best if new. You may also want to get new Thackery washers as they wear out with use and don't retain the original level of stiffness when reused.

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PostPost by: Pete M » Sun Jul 05, 2020 11:38 pm

Mine is the federal version.
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PostPost by: SENC » Mon Jul 06, 2020 12:43 am

Pete M wrote:That's a whole lot of carburetors. Mine is just a rubber tube.


Here is a picture of the federal adaptor plate from another thread here, the balance tube is built in (the channels within it). This is what you have?

fedstromplate.jpeg
fedstromplate.jpeg (100.64 KiB) Viewed 176 times
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