Esprit Turbo project car - part3 - the further continuation

[Lotusfab]

Just found a great write up by Tim Engle, all sounds so very simple! 

[drdoom]

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  

[Lotusfab]

Thanks Steve I may look into that.

[Andyww]

I have this book, I could have brought it over the other day, LMK if you want to borrow it.

[Lotusfab]

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.

[Lotusfab]

WOW JUST WOW! 
 

What a difference a day can make! I just took it out for a test drive and no stumble at all. The engine in driving amazingly at all rpms. I took it up to 5000 rpm and it really flew! The solution was the choke. The 35 mm has transformed the car. I still plan on the rolling road, just to see what everything is doing an to ensure all is correct. The steering is perfect as is the balance. Its a different car! 

[drdoom]

Outstanding! Devil's in the details, so far as tuning is concerned.

[Lotusfab]

Still can’t believe what effect changing the choke size has had. My S1 has always drove extremely well and set the bar. I would say now the Turbo drives even better than the S1. Its a relief after so long to have perfected the acceleration. Your always scratching around in a no mans land with these changes.

[LOTUSMAN33]

Well done Fabian, many would have just accepted the stumble but as usual you persevere to get things just right. A turbo driving well is such a rewarding car to own as well. 👍🏻
 

Dave  

[drdoom]

2 hours ago, Lotusfab said:

Still can’t believe what effect changing the choke size has had. My S1 has always drove extremely well and set the bar. I would say now the Turbo drives even better than the S1. Its a relief after so long to have perfected the acceleration. Your always scratching around in a no mans land with these changes.

It's worth considering that your focused efforts in sorting the other carb settings are largely the means by which you've arrived at this most pleasant outcome. Be assured the slight reduction in choke size did nothing more than enrich the transition point which, though it may well have been helpful, is subordinate to the accurate balancing of float heights and throttles in terms of running behaviour. 

Cheers!

[Lotusfab]

Thanks Dave. Steve, Interesting point. The only changes made were float height and choke. When I tune these cars I always found on my S1 there is a position on the idle mixture screw that gives a big boost in power output. Its not very wide probably in the 1/4 turn range. On my turbo I have never been able to reproduce this effect to the same extent. I noticed this time when I tuned it I was able to locate the position and the effect was similar to the S1. Was this due to a change in float height?
I don’t really know. All I can say is its now running perfectly. I would know for sure If I switched the chokes back and the stumble returned. Because of the work involved and the fact my car is now sorted I will not do this at this time. Maybe someone who has a stumble they can’t get rid of might try using 35 mm chokes and report the effect? Thanks for all the helpful advice and discussion it has really helped to sort my car! 

[LOTUSMAN33]

@Paul Colemanwas saying he had a stumble on his S1.

[Lotusfab]

Oh yes I’ll tell him.

[Lotusfab]

If anyone is thinking of replacing the original limiter rotor arm I have just received a shallow replacement from PNM engineering. The normal size Lucas won’t fit.Be sure and ask them before your order. Can’t believe the speed at which they are getting parts out these days. I ordered in the afternoon and received it the next day, only having paid for first class post. Well done PNM and thanks! 
Well just as it was going so well I have detected an unusual noise when the engine warms up. It sounds like a bearing. I used a stethoscope and believed it was from the reconditioned alternator. I disconnected the belt to check and its not from there. I now believe its the tensioner bearing. This new bearing has only done 700 miles. I then look back through the conversations on the internet and find some of these new bearings are useless and prone to failure. Having paid £50 I find this very annoying, especially as I now have to dismantle everything again to replace it! 
This time I am installing an SKF bearing as per the original Lotus spec. 8 have also invested in a Gates Kriket. Its easier to use than a Burroughs gauge unless you have the cantilever Lotus version. I shall also be using the MK1 Lotus finger and thumb as a cross check! 90 degrees max twist on the belt. 
Its very annoying, just as I have perfected the acceleration. I am very pedantic with the engine and always check everything regularly, which is why I detected the noise. Its fairly faint, but now the tappets and rest of the engine are so quiet you can hear every little extra sound! After the last rebuild the tappets were noisy, even though they were set correctly at install. After 700 miles I took the towers off and found some of the clearances had increased to the upper limit. Because everything was new I guess they were bedding in. I adjusted them down and now its extremely quiet with no tappet noise. The downside of this is you can hear so much more.

[Chillidoggy]

The valve clearances opened up? Presumably between the cam lobe, bucket and shim?

[Lotusfab]

Yes, when I measured and shimmed them they were all spot on. I checked and double checked, I have a lot of practice at this now! The tappets were noisy only on the rear of the engine. I took it apart and found the clearances on the end two had increased, but from memory only about 1 thou. Maybe because everything is new it had bedded in after 700 miles. Anyway I put thicker shims in and its perfect, no tappet noise.

[Lotusfab]

Update

New tensioner bearing fitted. I tensioned the belt for the first time using frequency and feel rather than the Burroughs gauge. I used the Gates Carbon drive frequency App for bicycles. At 30 degrees before TDC I tensioned the belt to 100 Hz. Being paranoid I then took the car to Tim at Lakeside engineering near Woking. Anyone around the area go no further than Tim. He is a real enthusiast Lotus trained expert. Whats more he has the correct cantilever Burroughs gauge. I was surprised, my tension was exactly on the single line marked on the gauge! Happy days. He then kindly topped up the trunnions - a job I was not looking forward to. I shall now be using Tim exclusively for any work I don’t wish to do. He saw the original ski racks in a Lotus training room about 25 years ago, they were the subject of discussion!  Heres a link if you need a decent and very fair Lotus expert.

http://www.lakesideengineering.com
 

With renewed vigour I cleaned it.....

[910Esprit]

Based on all the advanced jobs you have done on your car, I'm puzzled why servicing the trunnions should concern you!   You just need a dedicated 'grease' gun full of EP90 and you can charge them with the car on full lock, still on the ground.   As they should be done every 1000 miles, or so, you don't want to be taking it to a garage!

NB - They have fairly recently updated Gates Carbon Drive with a new version, that retains a history of the last several tests.   I prefered the previous version that just did 'spot' checks and didn't have an annoying introductory video.  I tend to run mine at nearer 110htz, but that's personal preference.  

[Lotusfab]

I went there for the belt check and remembered I still had to do the Trunions. Well it was on the ramp, a 2 minute job and he already had the gun ready, made perfect sense to save some time. 
I have never seen the correct Lotus cantilever Burroughs gauge until today it has only one mark at 95 and a safe band above and below. What was remarkable was it was tensioned exactly to the mark, I mean exact not even a mm off!  I found the Krikit erratic and inconsistent, probably because there is a belt align ridge on my version. Having proved it works and for simplicity I will only use the frequency method going forward.  
The car is at last sorted. Very smooth and no stumbles, not even slight its now spot on acceleration. I still plan a rolling road just to see how it checks out with all the sensors connected. Time to rack the miles up! 

[Lotusfab]

Finally made it to Northampton motorsport. I actually managed to get the car to a level where it was very drivable, from a stumbling nuisance through determination. The solution to the stumble was a smaller choke. I wanted to know exactly what was going on in cold hard stats, so I took it along. I am very glad I did. They discovered the throttle needed adjusting. Interestingly the return spring was fouling the throttle arm! This in turn was preventing the throttle from fully opening. A testament to the power this thing puts out I hadn’t picked up on it! We removed the spring and throttle cable holder and bent the spring part away from the arm. Really poor design that this is required to allow full throttle movement. Not enough clearance could result in a stuck throttle! Well it was an easy fix. 
 I was running a 43 idle jet. Very slightly lean in the midrange. We switched to a 45 and now its very slightly rich in the midrange, after a quick retune it is now as near perfect as it can be, it really shifts! I didn’t allow a full power run, as I will never drive anywhere near the limit, but at about 75 per cent throttle it achieved about 180 Bhp. 
I have done over 1000 miles now and it was a joy to drive the 85 miles after the tune. Well sorted at long last - no more projects for me! I intend to enjoy driving both my cars. 

[Bling]

Great result - enjoy the open road Fabian

[Lotusfab]

Thanks.

[LOTUSMAN33]

Well done Fabian, a well sorted turbo is a joy to own and yours is up amongst the best.

Its not easy finding rolling road tuners these days who understand carbs but sounds like you hit gold.

Nice image outside the garage, shows the turbo lines really well.

Dave  

[Andyww]

I noticed that issue on mine. The bracket which holds the throttle cable and end of the spring, mounted to the plenum, was bent. But when I straightened it, it caused the lever to hit the end of the spring so had to bend it back out of true again. Presumably all these cars are like that.

[Lotusfab]

Thanks Dave. Yes, crazy design that you have to bend something out of shape for it to work!