1989 Caterham Super Sprint Refresh

[Origin7]

On 11/17/2025 at 6:34 PM, MV8 said:

I just realized what this is. The car originally had a cable clutch but someone adapted it to hydraulic using a universal slave. 

 

@MV8 I can confirm this. It looks like there was a conversion that Sevens and Elans provided during this era. Here is the document I found in the manual. @NSXguy It looks like your car had this as well.Seven_clutch_conv.pdfSeven_clutch_conv.pdf

[NSXguy]

10 hours ago, Origin7 said:

 

@MV8 I can confirm this. It looks like there was a conversion that Sevens and Elans provided during this era. Here is the document I found in the manual. @NSXguy It looks like your car had this as well.Seven_clutch_conv.pdfSeven_clutch_conv.pdf

Correct- have shared similar observation before that it wasn’t a coincidence that many period lotus and caterham 7s have this typical blue pull-style slave cylinder installation/conversion. The web is littered with exhibits.

Now we have proof in documentation of the bulletin. Thanks for sharing . 
 

Most of those installs would be pushing 40yrs in service and should be considered  

to be past useful life and in need of replacement. 

[Origin7]

I ended up having Automotive Restorations go through my car to address a number of items, with the goal of making it as reliable as possible. Highlights of the work included:

• 123 Ignition installation

• Disassembly, cleaning, and rebuild of the carbs

• New alternator

• New plugs and wires

• Silicone radiator hoses

• New fuel lines

• All fluids changed

• New clutch slave cylinder

• Thermostat

• Water pump

• Falken Azenis RT615K tires

Overall, they did an excellent job and I am very happy with the results. The car runs well and drives smoothly.

 

My original plan was to modernize it a bit and make it more track-focused. However, this is such a well-preserved late 80s Seven that I have decided to leave it largely as-is and enjoy it for what it is. Aside from the cycle wings, it is essentially unmodified, and after driving it, I do not feel like I am missing anything. The older character of the car is really enjoyable. For now, the plan is to refresh the interior carpeting and put miles on it.

 

One area I want to dial in further is the Weber carb setup. After the car idles for a bit and I give it throttle, I get a noticeable puff of grayish smoke. I am also seeing black soot inside the exhaust tip. The compression checked out fine, so I do not think it is valve seals.

 

My suspicion is that it may be running rich at idle. They installed 28 mm chokes, which may be on the small side depending on the current jetting.

If anyone has recommendations on a good baseline setup for a Crossflow with DCOE 40s, I would really appreciate the input.

 

 

 

[JohnCh]

28mm is small. Below is a screenshot from Tony Weale's book:

[IamScotticus]

 Ran my DCOEs on 37s.  I've read that Chokes make more difference for off idle than at full throttle, or, the slow drive benefit may be more beneficial than the loss at the high end.  It depends on what the car likes and what you want.  Try bigger Chokes if you like but don't be surprised if you put the 28s back in

 

Get a fuel pressure regulator if you're running an electric fuel pump.

 

Running rich at idle may not be a real problem   it's hard to achieve a perfect balance with these. You may need to be rich at idle so you you're not lean off-idle.  Properly dialed in you may be spitting gas out the pipe.   Its a 1960s engine, expect it to break all the rules.

 

You can get hotter plugs, plugs with multiple electrodes and put in a MSD to improve low speed driving, although I will say Advanced Distibutors say MSD doesn't do anything.  Those who use them like them.  Get the one with a Rev limiter and set the cut at 6800 to save your crank.

 

More than helpful, 

Edited March 19 by IamScotticus

[NSXguy]

Awesome, she looks soo good. ARI did the heavy lift, now you get to do the fine tuning! I would recommend you have a wideband o2 sensor bung added to your exhaust after your merge collector. This will help with the next step of optimizing AFRs. (you can do it other ways, but this is my personal preference even if just to use during tuning)

 

1-Based on your engine spec, if you wanted improved idle performance and driveability at low loads, you can choke down at the expense of performance at higher loads but i agree with above that 28mm is too small and likely causing overly rich running condition (depending on current jetting, especially when cruising). Mine is close to 1700cc and i run with 32mm chokes (have run as high as 34mm on track) but also have aggressive cams- its a balancing act with carbs. I would expect ARI set the floats to spec for DCOE 151s which are the carbs you have. Having the floats set differently will also affect your final jetting and performance as well. Based on what i see in the photos, the 4-1 exhaust and short trumpets on the DCOEs, the engine is likely setup to breathe and perform up top, so you'll want at least 32 if you want it to perform as designed, but it will also run choked down to 30s as already mentioned with the appropriate jetting. 

 

2-Based on your engine spec, your timing may need to be tweaked as well (so it's nice that you already have the 123 ignition module installed). Even if your engine was standard spec, you can optimize the advance curve for better performance. Curious, di you get the bluetooth or the USB version of the dizzy? i have the bluetooth version for the 7 and find it really convenient for tweaking on the fly as opposed to the USB version i haven in the renault. 

 

You can post your current settings and jets (idle, mains/air corr. ,  accel pump, mixture turns, ignition, fuel pressure etc) and we can help/advise from there as you get on with the tuning or message me offline if your like. 

[Origin7]

This is excellent! Thank you all for the help. 

 

I've reached out to ARI to get more details about the setup and see why they swapped out the 32mm chokes for 28mm. After hearing from everyone and considering the symptoms, this appears to be my issue. 

 

@NSXguy The o2 sensor is a great idea. Welding on a bung is now on my to-do list. I got the Bluetooth version of the 123 ignition. It's really fast and easy to connect to. No regrets there. 

 

Here is the timing curve that ARI had loaded. I think it's a bit flat and could probably be advanced. I am getting some minor spitting through the carbs at idle, which could probably be eliminated.

 

More to come on the carb setup. In the meantime, it's time to start cutting some carpet! 

 

 

 

 

 

 

[IamScotticus]

Unless you have a steel crank, which Cat did not put in those engines, you should stay below 7K on the revs.

Apparently ARI didn't know this.

Sorry to troll on your thread.  Dont FU your engine.

Edited March 19 by IamScotticus

[Origin7]

1 hour ago, IamScotticus said:

Unless you have a steel crank, which Cat did not put in those engines, you should stay below 7K on the revs.

Apparently ARI didn't know this.

Sorry to troll on your thread.  Dont FU your engine.

 

Thanks! It's mapped out to 8k rpm, but there is a 6K rev limiter in there, which is good. That's the lightest trolling I've ever received. Feel free to continue. 

[IamScotticus]

Troll alert:

High zinc oil (Valvoline VR1 20W50 is good and everywhere) 

End troll alret

[Origin7]

I removed the old red shag carpet and replaced it with "black" (more like gray) German square weave. It's my first time doing interior work, and I'm really happy with the way it came out. 

[IamScotticus]

Please, don't put that on the dash!

[Origin7]

2 minutes ago, IamScotticus said:

Please, don't put that on the dash!

Carpet on dash? Is that actually something people do? 

[IamScotticus]

42 minutes ago, Origin7 said:

Carpet on dash? Is that actually something people do? 

Well, they do padded dash covers, which in my opinion, is the equivalent.  

Everyone is entitled to do what they want with their car.  I just cringe when something isn't "7".  A posh dash definitely isn't 7.  It's a 7, dear people, not an Excalibur.

Edited March 27 by IamScotticus

[Origin7]

I'm working on establishing a good, safe baseline ignition curve before I start working on the carb setup. I am getting a lot of smoke after idling for a bit, so it seems like it needs to be advanced at idle. Hoping to do a quick sanity check here. 

 

Here is my current setup:

 

 

This is what I am considering - Fewer plotted points, adding advance at idle, and all in at 3k. Look about right as a starting point? 

RPM Advance 500 12° 1000 16° 1500 22° 2200 28° 3000 32° 4000 32°

[Origin7]

I am new to this, so feel free to critique my approach or tell me if anything here seems incorrect.   

 

I tried increasing the advance at idle, but the engine didn't seem to like it. It showed the obvious signs of too much advance. Long story short, I went back to the timing curve shown above. It's also worth noting that I confirmed with a timing gun that the timing value and RPM at idle matched what the engine was actually doing. This was just to confirm that the 123 system was set up properly.

 

With a reasonable baseline timing curve, I then jumped into the carbs. The shop set me up with 28mm chokes, 55f8 idle jets, f16 emission tubes, and 120 main jets. Idle mixture screws were set 2.5 turns out. The emulsion tubes and mains jets matched what @JohnCh kindly sent me for the factory setup. The shop insisted 28mm chokes and larger jets were a better setup than the Caterham factory setup . The plug color and the way the car was running indicated this was not the case (way too rich). So, I installed 32mm chokes and 45f9 idle jets. I also changed out the idle mixture screws, which showed some signs of overtightening or corrosion (maybe both) on the needle portion. 

 

I backed out the idle mixture screws 1.5 turns and fired it up. I adjusted the idle mixture screws per the procedure. Next, I adjusted the idle speed, then synchronized. Long story short, the engine is running much better. It idles more smoothly, no spitting back through the carbs, little to no smoke, and pulls through the mid RPM range really well.  

 

I have to say, setting the idle mixture screws is a bit difficult. I think I need to work on this more. I do get some hesitation/bogging when I am driving and crack the throttle from low rpm. It's not terrible, but I hope to eliminate this. My understanding is that this could be caused by being either too rich or too lean with the idle screws. 

 

I like @NSXguy's recommendation to add a wide-band O2 sensor. For someone just starting out tuning carbs, I think it would be nice to see the result of the changes I am making. This may be the next step for me.  

 

Anyway, I'd welcome anyone's feedback, especially on getting the idle mixture screws set well. I am definitely in the ballpark, but shooting for perfection . 

 

  

 

        

 

   

[IamScotticus]

Working out idle is a very hands on process done by feel and giving the engine what it likes.  I would stick to the good books and Tuning guides you get from Pierce Manifold and others and avoid rabbit holes.  This is a light car so you aren't rolling through the dead spots like a 4K pound car  you will feel everything.  If you're going to err, err on the side of rich.  At least you won't melt anything.

 

There are other things here I would like to critique, however.   This car shakes and vibrates; everything moves.  This is why Caterham used steel brake lines.  I have identified points where your heater hoses may be in danger of abrasion.  Also, I think the crankcase vent breather filter is likely going to become an oil collector/dripper in that position.   I recommend a longer vertical position or routing it to a mounted catch can/breather, even if you do have the OEM oil separater in place.  The upper rocker cover vent can also benefit from routing to a collector.  Both of these can be routed into a single catch can/breather.  It will keep the engine bay cleaner.

I also see a spark plug lead very close to a hose clamp that will get cut into. 

The rule is, if you can wiggle it,  the car is wiggling it.  Wiggle and see what rubs, comes lose and how now before it breaks on the road.

 

 

 

Edited Saturday at 01:14 PM by IamScotticus

[Origin7]

@IamScotticus All good points. Thank you for the feedback. I am with you 100% on the catch can. I've got one on the way. Also, I may eliminate the heater/hoses. I'd like to use that space for other things.