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Esprit Turbo project car - part3 - the further continuation


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5 hours ago, Lotusfab said:

Mmm thats interesting. The carb earth wire is touching the distributor body?

If this is in response to my preceding posting a clarification is in order. The spark loss path in my case was from coil to centre tower of cap through rotor via failed dielectric to the end of distributor shaft where the rotor is perched. I've never fancied that Rube Goldberg rev limiting rotor either, FWIW.

To be clear my Elan was always equipped with the plain rotor.

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The new red rotor arm doesn’t fit as its too deep compared with the original. I did a detailed examination of the old rotor and cap. 5A4F9AFB-B48C-4822-8E6B-E208C5C26F4D.thumb.jpeg.422f56d0e5b57032a4315b7ecfe4a4eb.jpeg I noticed part of the rotor has been removed, the bit that grounds to earth to limit the rpm. They have left one of the brackets. There is an earth button directly behind the bracket

Below you can see the earth bar. As rpm increases the centre part with two screws stretches out and contacts the bar. This is then earthed to the distributor shaft cutting off the ignition. 
The worry is I cannot find anything wrong with the cap or the rotor, removing the bar just stops it from cutting the ignition. The is a small chance of earth leakage through the clip they left on, but the spark would have to travel through some of the insulation. 
There is a small crack, but this also should not stop the spark. I am attempting to find a replacement just in case.

D0820B5F-9A5C-44FB-BE80-BB1EC1A15868.thumb.png.28d955684f34109e9c58d0718a90197c.png

799FC14A-6015-4111-9944-D6897D78A07E.jpeg

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Yep, but I don’t think thats the problem. I took the distributor off. Very easy to do with the correct technique. Left hand through front under carb. Right hand under plenum. Distributor cap on and off by feel. Clips by screwdriver from front. I did all of the manual Lumenition testing for a third time including all the voltage tests. It passed with flying colours and no loose connections. I then examined the spark in detail. I noticed when it appeared not to spark there was a discharge on the ceramic. I asked my self how is this possible and realised it was covered in carbon, which is a conductor. I believe the ignition is working perfectly, but the plugs are carbon fouled. This is preventing a spark across the electrode so the engine won’t start. Solution - clean the plugs! It make sense because when I switch out the idle jet and holder I didn’t retune and set off around the block. The performance degraded and was poor when I got back. The next day I switched to smaller chokes and couldn’t start. If it was running very rich, it makes perfect sense why there is not spark. Explained here....3F683723-41E5-49FB-B045-5E12D2FFA4DD.thumb.png.1eda89956051f385e97f17b4909a2044.pngI should have thought of this early on, but I have never had this problem with any engine up until now. Then again I have never made such large changes to the carbs in one go.  I will clean the plugs and let you know if I am correct! 

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Cleaned the spark plugs and she fires, but won’t sustain. 8 have to reset the ignition timing. Its now flooding. This maybe caused by the smaller chokes. At least I know what caused the ignition issue. Should now be able to get it running.

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No, no. Smaller chokes will not flood otherwise properly set carbs. Look to float heights and/or fuel pressure for resolution, certainly if the flooding is at point of starting or idling. 

Again, all a minor reduction in chokes will accomplish is to bring on the main circuits at an earlier point. This may well incur increased richness from then on but should be incremental, rather than wholesale. 

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Float height I am sure is spot on as is the fuel pressure. Won’t the smaller choke increase the venturi effect and suck more fuel into the chamber? So the idle screws will need to close more? I have replaced the idle jet and holder with the originals. The only difference now is the choke size. 

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On any car running these Dellortos the mains circuits are utterly separate from idle/slow run until well underway. The chokes offer no venturi effect until substantial airflow is established, well past idle/slow run or light cruise conditions. It is natural vacuum which drives fuel delivery of the idle/slow run, entirely dependent on the airflow being largely restricted by the throttles thus negating venturi effect. As mentioned, one may start and run the engine with the main clusters entirely removed, consistent with the preceding summary.

Cheers

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Mmm thanks, in that case. I will try again.

Given the above the engine should start. All I can do is set the static ignition timing and try again. Maybe I flooded it with choke and accelerator in my eagerness for it to start.

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  • Gold FFM

I send mine up to Watford Exotics once a year and it starts every time on the button and has done ever since I have owned it  Just saying 

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Ok to recap so far

I switched the idle jet to a 58 and weakened the holder to 7850-9, HC config. I ran this with the LC 36mm choke to test the changes. It started easily and after about 15 minutes started to misfire. It still stumbled on acceleration from about 2600 rpm to 3000 rpm.

The next day I switched to the 35mm chokes. The car wouldn’t start. I found there was no spark. As we know now there was no spark across the electrode because it was discharging along the insulator due to the carbon.

I cleaned the plugs and the ignition is working again. 
The progression circuit seems too rich, so I switched back to 43/7850-7 with  the 35 mm choke. It won’t start. I am guessing this is because the idle mixture and ignition timing are off(I had to remove the distributor for testing).

Tomorrow I plan to set the static timing and try again with a fully charged battery.

Since there is no manual adjustment of the progression circuit(except by switching jet and jet holders) maybe the 58/7850-9 is too rich for my car? 

 

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You need to go back to square one and start again Fabian!

Return carb to 100% standard and dynamically set the timing, as per book.

I recall you mention that you had corrected the float hight a couple of days ago.  This needs to be checked in isolation before you move on!

 

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Sound advice on reverting to baseline, to which I'd add make but a single change at a time. No success likely when chasing too many rabbits at a time! Also expect trouble will be found in error of assembly or float setting. It's rare for coincidental failures to blind-side an effort, so let's keep ignition related concerns limited to clean plugs.

Rigorous discipline is always in order when fiddling with carb jetting. Static ignition settings much less so.

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Thanks. I am certain the float height is correct. I measured the height in the bowl after setting them to 15 mm, without compression of the piston on the end of the needle valve. I think this is where an error occurred before. If you hold the float vertically hanging down, as the book suggests and set 15 mm the piston may be compressed. You have to watch it carefully, which I have done this time. Last time I also checked the level with a vernier caliper. I think its tricky to measure the fuel height like this unless lighting is very bright.

I will set the static timing to 12 degrees to get it started and when running set the timing to 26 degrees BTDC at 3000 rpm. I have retarded it by 2 degrees to allow for increased compression, It was running nicely at this setting before.

I have put the original jet and holders back in. The only difference to before is the idle screws are out of ideal position (this shouldn’t stop the start) and the choke is smaller, but as discussed above that probably doesn’t affect the idle circuit. 
So far it's not behaving as I would have expected. I will just keep going until its sorted. I post it all here so anyone else thinking of doing this has a base line guide. 

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TE is a very sound and knowledgeable chap for whom I have the highest regard. That said he might defer to Keith Frank in terms of understanding the workings of these carbs. What KF has determined over years of dedicated and highly methodical work sheds much light and belies some of the folklore taken as common knowledge. Should you wish to take a deep dive into this you'd be well advised to get on the Sidedraft Central board and ask to be brought up to speed on the vital criteria.

Cheers  

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Thanks Andy, I have that already.

Car is now running and retuned. The start issue was the ignition timing, which is now reset. I have tuned it again and its spot on.

Its running a 43 idle jet 7850 -7 jet holder and 35 mm chokes. Just need the weather to change for a test. If the stumble is still there I will try a 45 idle jet. Trying to get this as close as possible before the rolling road.

The 7850-9/58 combination seems too rich for this engine. Maybe the progression hole drillings in the body are the reason? Anyhow the combo doesn’t work in this engine.

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