Lotus Elan

Stomberg mixture puzzle

PostPost by: gus » Thu Jul 30, 2020 11:58 am

There are too many things going on here to rationally figure out what is causing rich mixture on a car that reportedly runs well

On CD2SE carbs one can adjust the mixture by removing the pistons, loosening the setscrew and sliding the needle up and down then tightening

Other things that can affect mixture

oil in dampers
what springs are in the carbs
are the temperature compensators working

First I would buy Lotus needles, changing to some unknown needle can have unknown consequences

B1Y B1AR or maybe some others. I think B1G was the emissions needle
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PostPost by: steve lyle » Mon Aug 03, 2020 9:04 pm

We went on a drive yesterday, about 325 miles. Oil was topped up when we started, it looks now like it's down about 40% of a quart, which works out to about 1 qt every 800 miles.

And attached are shots of the plugs after that drive.

2,3 and 4 look pretty good. Maybe appear to be a bit on the rich side, but the car ran great, started easily when hot - I'm not going to complain. #1 is a bit oily, so it looks like that's where the oil is going - rings or guides, I don't know.
Attachments
IMG_0465 (2).JPG and
#4
IMG_0464 (2).JPG and
#3
IMG_0464 (2).JPG and
#2
IMG_0462 (2).JPG and
#1
Steve Lyle
1972 Elan Sprint 0248k @ https://www.mgexp.com/registry/1972-Lot ... 48K.30245/
1972 MGB Roadster @ https://www.mgexp.com/registry/1972-MG- ... 842G.4498/
2007 BMW 335i Coupe
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PostPost by: david.g.chapman » Tue Aug 04, 2020 6:21 pm

Hi Steve,

Both of your pics of No. 1 plug seems to show an oil deposit, more so on the second pic after that long run. I an sure you have checked that it is not unburnt fuel, as it would evaporate after a few mins, and there is no misfiring.

Incidentally your cylinder 2 and 3 pics are the same, so I am assuming both plugs look like the pic shown.

It might be worth checking the compressions again and posting the figures after this run for comment. Anything less than 160psi for a low compression Federal head of maybe a bit more for a high compression head would confirm a problem, especially if the other cylinder compressions were more than 10% higher.

Then I suppose its head and sump off time to measure bores, look for broken piston rings and check on valve guide clearances. :(. Or live with it for now.... Unless someone has any other thoughts?

Dave Chapman.
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PostPost by: steve lyle » Wed Aug 05, 2020 4:07 am

Compression #'s:

Cyl Dry Wet
1 165 170
2 155 165
3 170 190
4 175 175

I did my best to use the same process on all the cylinders - I couldn't exactly measure the amount of oil in each, but they all got three pumps of my oil can, which should be about a tbsp, maybe a bit more.

155 to 175 is too wide a variance by a bit - I've always heard 10%, and that's about 13%. And I have no clue why #4's results are the same, wet or dry, other than the rings seal great, and they can't get any better? Or why #3 is pretty good to begin with, but then goes way up - maybe the chamber is just smaller, and the rings are so-so?

In any event, any oil getting into #1 is likely coming down the guides, correct?

The collective's thoughts?

And Dave - thanks for the catch. Here's the correct pic for #2.
Attachments
IMG_0463 (2).JPG and
Plug #2
Steve Lyle
1972 Elan Sprint 0248k @ https://www.mgexp.com/registry/1972-Lot ... 48K.30245/
1972 MGB Roadster @ https://www.mgexp.com/registry/1972-MG- ... 842G.4498/
2007 BMW 335i Coupe
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PostPost by: gus » Wed Aug 05, 2020 12:00 pm

A guide losing that much oil would be pretty thrashed.

It occurs to me that the high pressure oil feed is adjacent to the #1 cylinder

Try a leakdown test

Not fun but a bad head gasket is better than a head rebuild.
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