Lotus Elan

Problem with #3 cylinder

PostPost by: davidj » Wed Aug 30, 2017 11:41 am

Good afternoon,

I hope someone can help me. I have long suspected my elan has a problem at low revs so I took it to a specialist garage, who identified, at tick over, that the exhaust manifold of number three cylinder is running cooler than the rest, which suggests a misfire. He used a heat sensing camera.

He then checked the compression, which was ok, and coupled the ignition circuit to a computer to check the leads, plugs, coil and distributer cap. All are OK. No leaks in the manifold either.

After that he started to scratch his head. Has anyone any idea what the problem could be?

Thanks in advance.

David
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PostPost by: rgh0 » Wed Aug 30, 2017 11:49 am

If the ignition and compression is OK then it is probably idle air flow and mixture. You need to work on getting balanced air flow at idle with No3 the same as the other cylinders and getting the mixture needed for No 3 to fire.

If the throttle shaft is twisted then No 3 could be to much closed closed while No4 is correctly set and firing at idle. Once the air flow is correct then you need to adjust the idle screw to admit the correct amount of fuel. I there are air leaks into No 3 from the shaft seals or the manifold O rings then these need to be stopped .

cheers
Rohan
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PostPost by: davidj » Thu Aug 31, 2017 12:08 pm

Thanks for your reply. It would not occur to me the throttle shaft could twist. I checked last night and both of the discs looked to close, although I don?t know how much of a seal is required. Alternatively I guess the idle jet for #3 could be blocked?

The mechanic suggested valve clearances but I cannot see how this could be the cause unless they were massive, in which case the compression would be effected.


Cheers,

David
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PostPost by: Chancer » Thu Aug 31, 2017 2:42 pm

Likely to be idle balance or mixture on that cylinder, you cannot see if the throttle settings are the same by looking down the venturis, you have to remove the progression hole covers and shine a torch down to see the relative positions of the butterflys, it will be a miniscule difference.
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PostPost by: mbell » Thu Aug 31, 2017 5:42 pm

The air flow is also effected by clearance between butterfly and barrel. So you need to test the actual airflow when running.

You can get a nice tool* for this or some people do it using a length of hose and listening....

* https://www.amazon.com/Latest-Rage-Delu ... B00CMC57R0
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: Craven » Thu Aug 31, 2017 6:22 pm

Colortune is ideal for this type of problem, not only can the mixture be checked but a missing spark a low RPM is also obvious.
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PostPost by: Grizzly » Thu Aug 31, 2017 6:56 pm

If it's just one cylinder make sure the cold Starter Valves are fully closing and not sticking ;) as i found out with mine they tend to make one half of the carb run out of balance with the other half (mine was running rich too, that meant the idle screw wouldn't weaken it enough and would run with the idle screw fully in).

If you still have leather spindle seals it's worth changing those too (they tend to dry out and cause air leaks)
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PostPost by: Elanmans4 » Wed Mar 28, 2018 11:57 pm

Hi, did you find the cause of your problem, I have the same issue but on number 2 cylinder
Thnaks. Shaun
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PostPost by: fatboyoz » Thu Mar 29, 2018 5:59 am

Hi Grizzly,
How did you discover that one of your cold start valves was sticking? What did you do to remedy same?
Cheers,
Colin.

Grizzly wrote:If it's just one cylinder make sure the cold Starter Valves are fully closing and not sticking ;) as i found out with mine they tend to make one half of the carb run out of balance with the other half (mine was running rich too, that meant the idle screw wouldn't weaken it enough and would run with the idle screw fully in).

If you still have leather spindle seals it's worth changing those too (they tend to dry out and cause air leaks)
'68 S4 DHC
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PostPost by: Elanmans4 » Mon Apr 02, 2018 1:43 pm

Many thanks, for the advice, tried both and still have an issue,
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