Opening can of worms

[Bryan Boyle]

I've been running with NGK BPR7ES plugs since I restarted the engine last year...and, while the car runs ok on them (I should mention that I'm running the Pertronix dizzy and 40KV matching coil, aprx 5 degrees idle advance at 1k idle), I still notice, in city traffic that I have a tendency to foul the plugs, which I have gap set for 30 thou, and the european needles in the strombergs.  AFAIK, the balance is still on (though, I've gotten some advice that going to the US needles may show an improvement; when I rebuilt the carbs last year, I reused the euro spec to get the engine running...can always put the mercury sticks on them again and double check balance)

Not to go too deep...but a couple q's for the assembled masses (understand, this is my first TC I'm dealing with here...lots of experience with the french motors...but engines are engines, right? 

1. US vs Euro needles.  All things being equal, 3 of the 4 plugs have carbon deposits; one plug is a nice tan insulator.  Will changing to (what I assume) is a leaner (US) running needle, rebalancing, etc. get the ratio back to where it needs to be?
2. Running one notch hotter plug (such as a 6ES)?  Thinking that will be masking the issue while moderately assisting in burning off the soot but tossed it out there.
3. Is 5 degrees advance the number to shoot for at idle on US engine?  Thinking that if it's not advanced enough, then there is incomplete not enough time to fully combust the charge in the jug, which will lead to deposits...can always add a couple degrees in (and readjust the idle speed) if 5 is not copacetic.

Seeing as the lump will come out soon (been saying that for months...steeling myself to just get on with it, but work and travel gets in the way...) to do the head and clutch, I don't want to go too deep but give me another month or so of headroom.  Guess I'll find out the condition of the existing when I go to swap it out with the O/H head standing ready, but just thinking of options to get me through the next 60-90 days till I bite the bullet with the Big Job.

Useful suggestions or insights welcome, flames to /dev/null, ok?

[BDA]

Sorry I can't help you with your needle question but NGK 7 plugs are probably too cold for a TC. I've been using 6s (BKR6EIX to be exact) in my motor (I know it's not the same motor) but also the general consensus on the Elan forum is that 6 is the proper heat range.

5° BTDC statically timed is called for in the manual. I've been told that the Pertronix dizzy can be statically timed. I don't know how that works because I think the guts are Ignitor II or III which can't be statically timed. If it can't be statically timed, you'll have to get a dynamic timing spec from someone.

[Bryan Boyle]

Sorry I can't help you with your needle question but NGK 7 plugs are probably too cold for a TC. I've been using 6s (BKR6EIX to be exact) in my motor (I know it's not the same motor) but also the general consensus on the Elan forum is that 6 is the proper heat range.

I'll run over to Advance Auto and pick up a sleeve and try them (short term, maybe 50-75 miles and see).  Can't hurt.  Looking at the specs, the heat range is higher, but not hundreds of degrees. 

5° BTDC statically timed is called for in the manual. I've been told that the Pertronix dizzy can be statically timed. I don't know how that works because I think the guts are Ignitor II or III which can't be statically timed. If it can't be statically timed, you'll have to get a dynamic timing spec from someone.

When I got this beast running last April (a year already?  Yikes!), it was pretty much (if you recall) 'push through to get it going reasonably well'; now that a year has gone by...want to fine tune the mechanicals (you should see the stock of new parts in my garage just waiting...once I get off this work travel treadmill...Jan 31, 2024 is it!) now that I know the car can go down the road.  Thinking I will try dialing in a couple degrees advance, taking out on the road, seeing what the response is...and doing the 'kill engine on side of road and pull plug to see' (used to set my bike using that method...) thing. 

[Clifton]

The only way to know if your AFR is good is a wideband. https://www.amazon.com/AEM-30-0300-Wideband-Sensor-Controller/dp/B0184TSI84

It may seem pricey but you will know everything there is to know in 5 minutes of driving.

I had an old bike that was either lean at WOT but good at cruise or the larger jets were good WOT but rich at cruise, low 13's. No way to know without a wideband. You can make a tail pipe extension if you don't want to weld a bung on your permanent exhaust.

I set timing with an adjustable light so I know what total timing was after the mechanical was all in. If your marks only go to say 10* on the pulley, you can turn the dial 20* to keep in on your pulley and just add the 20* to your pulley number.

[jbcollier]

I agree with BDA that you should use 6's.  Though, myself, I would switch to 7's for a track day.

The stock Stromberg carbs were a pure emissions carb as there is no way to properly fine tune the mixture.  Sure there's an idle air bypass to trim but it doesn't actually change the mix when wide open.  I strongly recommend switching to adjustable dashpots so you can properly set the mix.

Also keep in mind that variable-venturi carbs are extremely sensitive to tight valves.  Always make sure your valve clearances are to spec before dialling in the carbs.

In regards to timing, you have the wrong end of the stick.  What matters most is the upper end of the curve.  Too much advance and you might hole a piston flat out (say climbing a pass in the mountains), too little and you are losing power and economy.  The twin-cam actually has pretty nice chambers when the squish is set up properly.  General consensus is that 28° maximum advance is what you want for racing/track day.  You could go to 30° for normal hard driving but I wouldn't go any more.  In contrast, the Renault engine can go to 32°/34° with 36° possible for normal/no-mountain-pass driving.

So set your maximum advance and let the idle setting fall where it may.  I then note the idle setting so I can quickly check the timing in future without having to rev it.  If you want to change thew idle setting, you have to change the distributor's advance curve.  Tighten it up by limiting travel if you want a higher initial setting, for example.  Here's where the 123ignition programmable distributors really shine.  You can dial in any curve you want.

[Kendo]

JB, I’m not familiar with the term dashpot for the Strombergs. Is that different from the adjustable needles?

[jbcollier]

Forgive my use of a general term.  More accurately called "piston" or "air valve".

[Bryan Boyle]

JB, I’m not familiar with the term dashpot for the Strombergs. Is that different from the adjustable needles?

That's what I was thinking; I have the adjustable needles in both Euro and US Emission tapers.  Right now running with the Euro set.

Maybe I should just consider getting Barry's single weber conversion or the Mikuni kit that I've seen floating around...Advantage of the weber is that they are massively adjustable (I had the conversion on my S2 and had it dialed in extremely well for town/motorway work); the Mikes are well-known and lots of info out there about them.  The Strombergs work...but were built with a lot of compromises.  I guess if Lotus had had the $/UKP, they could have worked it out...

Leaning towards the Mikunis and concours originality be damned.  Want this buggy to run well. 

http://www.v-performance.com/products/air_fuel.html

[jbcollier]

If you have the adjustable needles, then why not tweak them?

I carefully check the valves, compression, timing and then bottom out the accel valves and the idle air bypass trim screws.  Then do an initial sync.  Next I adjust the "idle" mixture using the adjustable needles.  Use a screwdriver to lift the piston/dashpot 3-5mm (with SUs it's 1.5mm but the Strombergs need a bit more).  If the idle speed goes up and stays up, it is too rich/lower the needle.  If the idle speed falters, then it is to lean/raise the needle.  If the idle speed rises and then rapidly falls, that's perfect.  Double check your sync if you made large changes to the needle height.

Use Dexron 3 automatic transmission fluid in the carb dampers.  Engine oil is too thick.

Now road test it and see how it drives.  At this point I would hook up a wide-band O2 sensor to double check the A/F ratio across the range of driving conditions.  You can tweak settings, lightly trim needles or fit other needles to get it perfect.  Once there, the really nice thing is that you just do a idle mix baseline again to reset for any major altitude changes.

[Richard48Y]

Same sensor is available at Summit Racing.
Free shipping and you eventually earn some money back.
https://www.summitracing.com/parts/avm-30-0300?seid=srese2&utm_source=bing&utm_medium=cpc&utm_campaign=Brands+%7C+A&utm_term=4582077271614146&utm_content=GSAPI+5ba0fb517989d

[Pfreen]

I attached all I know about twin cam ignition timing.  Hpv is the system I have on my tcs and I enter initial timing, 1000 rpm, 3000 rpm and 7000 rpm.  It linearly interpolates between the points.  It is a crankshaft referenced, wasted spark system.

It is obvious to me from the curves that the Federal ignition timing was retarded for emissions.  The curve shown is for a 10.2:1 cr, and sprint cam.  I Have never heard pinging.  Anyway, it was set for 12 degrees at 1000 RPM.
The data shown is from the Miles Wilkins book on the twin cam.
Since I did this curve, I advanced it 2 degrees because the higher lift and overlap cam than the sprint needed mor advance at 1000 rpm, but the max advance is the same as shown.

[jlmullen2]

Bryan -

I saw you referenced a single Weber conversion for a TC. I've seen a few photos of this but no information on manifolding or if it's available. Who is Barry? I'm not at a position with my engine to try this as it's still at my rebuilder but I like the thought of a simple single carb to replace the Strombergs.

Appreciate any information you might have on this conversion.

Thanks

Larry

[SilverBeast]

Bryan -

I saw you referenced a single Weber conversion for a TC. I've seen a few photos of this but no information on manifolding or if it's available. Who is Barry? I'm not at a position with my engine to try this as it's still at my rebuilder but I like the thought of a simple single carb to replace the Strombergs.

Appreciate any information you might have on this conversion.

Thanks

Larry

I'm assuming Barry is Barry Spencer from Spencer Motorsports. He's recently posted on the Lotus Europa Facebook group as he's just rebuilt several Twin Cam Engines. At least one of the pictures shows a single Weber.

[Clifton]

240Z's came with SU's that look just like the Strombergs. People would run twin DGV Webers because they couldn't get them to run right. The SU's made as much power and were simple and easy to set up. I would only do the Weber if it was a DCOE.

Looking at the timing curves posted. It's a lot before 4k. If there's going to be knock it would be around peak torque with that timing. Not saying it's bad but on motors at the limit of knock, octane, boost or compression, it could be.

[Pfreen]

I have twin Hitachi SU's from a 240z on my car.  They were installed when I bought it in 1986.
I have a af ratio o2 sensor installed.
The measured AF ratio is as follows:
Idle  13:1
low load 14.5  - 16:1 depend on speed. No misfires at lean
Wot 12.5:1

Mileage from 20-28 mpg.  Cam is as much as I would ant for a street car driven quite a bit.  It just drives the ac compressor at 1200 rpm.
However, 135 hp on chassis dyno.  It revs forever but the rev limiter is set for 7000.