Lotus Elan

Rich mixture Elan+2

PostPost by: Mrozik » Mon Jul 26, 2021 7:21 am

Hi All

I was wondering if the members could suggest other possibilities that could cause the following problem.

Since rebuilding the engine including new pistons and an overhaul or replacement of just about every component although the engine starts fine and initially runs well for 10 -20 miles. It then starts to run on 3 or less cylinders! When first started after the rebuild the engine smoked (black) quite badly and back fired but after some carb adjustments, this has since improved...

After the problem appears, removing the plugs show that they have all become quite sooted but cleaning them restores the the engine to running on 4 cylinders again.

To my mind the problem is surely a carburation one but I don't understand why it should so bad?

The Weber carbs were serviced - no jets were changed.
I intend to check the float levels but I was wondering whether new jets might also be required now that the engine is "new"?

The mechanical petrol pump was serviced - could the pressure be too high now?

A new distributor. HT leads and coil were fitted and they seem to work well - however as meanwhile I've converted the old distributor to electronic ignition, I was wondering whether fitting this, thus strengthening the spark, might solve or improve matters?

I have check the cylinder compressions and they are all between 165 and 170 psi so mechanically fine!

Is there anything else I should check?

Thanks in advance
Mrozik
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PostPost by: alan.barker » Mon Jul 26, 2021 8:40 am

Is the mechanical fuel pump as original with glass dome.
If it's a replacement all metal (made in India or China) they produce too much pressure and need a regulator.
Alan
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PostPost by: ericbushby » Mon Jul 26, 2021 9:07 am

I agree with Alan above but if the pressure was causing problems then that would show up when you check the fuel level.
Remove the round jet cover and one main jet stack. Measure down from the top of the float chamber.
Opinions vary but I am having good results with 29mm and this has cured my rich mixture problem.
I actually measure from the rim of the round jet cover hole which is 16mm above the top of the float chamber.
Therefore 29mm is 45mm from the rim.
I use a vernier depth gauge and a small torch. When the probe touches the fuel the surface will shiver.
A thin dipstick like a cocktail stick will work just as well.
Of course do this just after the engine has been running. It runs quite well without the main jets fitted.
Best of luck
Eric in Burnley
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PostPost by: Mrozik » Mon Jul 26, 2021 9:33 am

Many thanks for the advice.

The fuel pump is the original glass bowled mechanical type

Cheers
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PostPost by: EPA » Mon Jul 26, 2021 12:15 pm

The cold start device (choke) can cause this if it isn’t fully off or the cable isn’t allowing it to go off.
Give them both a push to make sure they are off.
Has their been two different versions of this post?
I replied to this earlier in the day and whilst I can see my reply in my posts it doesn’t appear here

Ed
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PostPost by: Mrozik » Mon Jul 26, 2021 1:30 pm

Hi Ed

I think I did see your reply before.....but it's disappeared now.....strange!

Cheers
Mrozik
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PostPost by: Mrozik » Fri Sep 10, 2021 12:55 pm

Hi All
Thank you very much to everyone for the suggestons. The problem is fixed, it turned out to be incorrect floats heights so a special thanks to Eric from Burnley for his tip.
John
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PostPost by: richardcox_lotus » Fri Sep 10, 2021 4:10 pm

Mrozik wrote:Hi All
Thank you very much to everyone for the suggestons. The problem is fixed, it turned out to be incorrect floats heights so a special thanks to Eric from Burnley for his tip.
John


So can you confirm the values you set them to please ?
Richard
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PostPost by: Mrozik » Fri Sep 10, 2021 4:20 pm

I checked the levels according to Eric’s suggestion and found that one was 10mm too high so i removed the tops and set the floats according to the workshop manual. Hope that helps.
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PostPost by: ericbushby » Fri Sep 10, 2021 7:24 pm

Hi John,
Thanks for the feedback That is how we all learn.
Eric
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