HypoJets and O-tubes on the way...

[gjz30075]

Thanks Simon. I like your float level method. I think it's the same level for the 151's?

Greg Z

[StressCraxx]

Simon,

Well done. The best I results I could get was with the 45F9s as well. The flat spot with the sprint cams, 32mm chokes and tube headers was from 1500 to 3000 RPM. Once above 3000rpm, it was great, with a good jump in power at about 5500 all the way to 7000.

I did reduce the flat spot by degreeing the intake cam right on spec. It was about 3.5 degrees retarded. It does not feel like I have lost anything up top, but hard to tell without a dyno.

How did it drive once you had the float levels at 25mm?

Regards,
Dan

[simonknee]

I've been running at the 25mm level since my engine rebuild in 2010. At the time I went to SE spec and started to suffer from the "dreaded flatspot". Going to the 25mm level cured this. It's annoying to have to take off the cover to adjust but you get the feel for the changes required.

It was at this point I did a bunch of work on the carbs. Starting with a full overhaul kit I made sure they were airtight. Then I went to work on some areas that get overlooked. The chokes can be a little baggy in the barrels and I got a fuel leak into the carbs from around the outside of the trumpets. I modified the springs on the chokes to give more a snug fit and used silicone sleeving as a gasket around the outside of the trumpets. No more fuel in the airbox for me. I replaced the carb linkage as this was old and worn. Then I did the best thing ever and drilled that hole in number 4 butterfly. When I got the balance just right the first time it is was so much smoother and quieter that even my better half commented on it - without prompting.

My current jetting/chokes is as per spec for an SE with 40DCOE18. So as long as you don't follow webers advice on the float level and don't do a "best lean idle" for mixture then it looks like they got it about right within what weber supplied back in the day.

Twincam SE C-type cam
45D4 (no vac) 10deg BTDC
Pertronix Ignitor II, 0.6 ohm coil
40DCOE18
chokes: 32mm
aux venturi: 45
idle: 45f9
main jet: 115
air corrector: 150
e-tube: F11
accel pump: 40

I did not want to go for Keith's custom bits until I had my LM-2 working properly. It is supposed to read rpm straight off the coil negative but with electronic ignition and a high power coil there is so much noise and inducted signals on the line that the unit cannot do it. A brainwave about utilizing the SpeedyCables circuit in my tach sorted this. This delay was good fortune since 2 years ago Keith was still trying to modify existing e-tubes. Once he had worked out what the problem was he then made his own. You can find all the info in his forum BUT it is difficult to sort the wheat from the chaff as Keith has detailed his entire journey - which is full of many eureka moments that turn sour. So we are all waiting on his new white paper that will explain all.

25mm is correct for 151 and the other 40DCOE that are fitted to the twink. However the important spec is really that it should be 2mm below the aux venturi passage +-1mm. Any higher and you are likely to get accidental sploshes down the passage. However measuring this 2mm is nigh on impossible so the deck inside the carb makes a suitable reference. If you look down the main jet hole you will be able to see a "bridge" which is the lip of the main jet. This should be 23mm from the deck so it is easy to check your carbs with the screwdriver technique.

[Jason1]

Hi Simon

Is your car left hand drive? I just bought a synchrometer but cannot get it into number 4? Even if I tidied the crazy brake line routing done by the PO I could not get it in the space left by the pedalbox. I plan to get the right angle adapter but in your pictures it looks like yours fits without? Maybe you get more room in the S3 than the +2?

Cheers

Jason

[simonknee]

No I am right-hand drive but the carbs are above the pedal box in an Elan.
You need a right angle adaptor.
There are all sorts on this page: http://www.alamomotorsports.com/weber/s ... izers.html
Maybe Aldon could order you the correct one.
But I reckon a trip to B&Q and get a bit of plastic plumbing!
http://www.diy.com/nav/fix/plumbing/plu ... d-11478384

[Jason1]

Cheers Simon

I just ordered this one http://www.ebay.co.uk/itm/390338941373? ... 505wt_1037

Keep up the good work.

Jason

[Ross Robbins]

This was on the Sidedraft Central forum posted by Craig Cooper about his visit to Keith Franck with his twincam powered Seven:

At the Feet of the Master

Traveled with my friend Hal yesterday from Chico to Martinez trailering my '76 Caterham Twincam to Keith's home garage. What a day! First, let me say, don't believe Mapquest. We got there a little after 9 and Keith hooked up his instrument to my newly installed O2 sensor bung and told me to drive for about 20 minutes. It turned out to be closer to 40 minutes with getting lost (can't blame Mapquest this time) Anyway, Keith entered the data into his program and made an initial determination for idle and main jets and emulsion tubes. We were slowed down a little by my having set one of the float levels improperly (never got the hang of the optical tool, even with Keith's demo) We tried several different "itterations" of e tubes, main and idle jets, test driving the car each time and reporting back to Keith.

Finally though, things came together and the motor smoothed out throughout the RPM range and seemed more tractable than it had ever before. I should mention we were working at Keith's home, my car is loud, and I hesitated to drive too enthusiastically for fear of offending neighbors and drawing unwanted official attention. However, on returning to my rural part of Chico, I unloaded the car and went for a short spin on the back roads. I was truly blown away at the car's performance. It idles smoothly, has very little hesitation in transition, runs smoothly at cruising RPM, and pulls stronger than it ever has to 7000. It's a different car! Striped assed apes and scalded dogs beware! Prior to taking the car to Keith, I was quietly trying to decide if I could sell it for roughly what I paid for it and move on to something else. Not for sale now, thank you very much.

Sorry to be so windy here, but Keith did such a great job and the difference in the way the car runs is so dramatic I wanted to share. I think it was vital though that Keith was there for the work. Had I been ordering parts, emailing or talking back and forth, etc. it wouldn't have happened. Keith says we can make it even better by correcting the position of the transition holes, but it's so nice now, I hesitate to touch ANYTHING. So, job well done! Next time I'll bring my tools (and my damned checkbook!) Thank you Keith, I enjoyed meeting and working with you and you are doing some truly amazing work on Weber carbs.

I know my S2 Elan has never run better than with these E tubes and Hypojets from Keith so, Simon, I think you're in for a nice treat!

[gjz30075]

I'm sure it was vital to be at Keith's house. I wish I were closer and I'm afraid the trial and error experimentation will be costly.

Greg Z

[JJDraper]

I've been lurking on this thread for a while and have now decided that I must try some of this! I have suffered from the low rev black hole in power, despite much tinkering, by myself and professionals. Some improvements after both, but not as much as I hoped. My recent summer hols showed this up with the low rev poor running causing concern. This is made worse by running a 3.55 diff - great for motorways, but a problem in first gear starts on a hill.

Currently the Webers run a treat after 3k rpm, but below this is a bit hit and miss. I suspect the plugs soot up after low speed running, so anything that makes the mixture leaner and keeps the power output stable must be a good thing.

Some expenses, but as I cover a fair old annual mileage in the +2, so even a 10% mpg improvement (which appears to be a conservative estimate based on the hype) will cover the costs pretty quickly. A serious programme of trials has still got to be cheaper than EFI!

First things first, subscribe to sidesraft central; establish all jet, tube & choke sizes; check/set float heights; check/set carb synchro (drilling a hole in the butterfly worries me!); then try these wonder jets!

Something to tinker with and take my mind of the whining diff...

Jeremy

[simonknee]

First things first, subscribe to sidesraft central; establish all jet, tube & choke sizes; check/set float heights; check/set carb synchro (drilling a hole in the butterfly worries me!); then try these wonder jets!

Make sure you do not have any airleaks or you will be chasing your tail.
There are a number of notorious points where webers - especially as they age - can leak.

After 3K you are mostly on the main circuit (this can be tested - see Keith's 2006 white paper).
Plus issues with balance reduce as the throttles are opened (obvious when you think about it)
So sounds like your issues are when you are running on the idle jets - which doesn't mean your idle jets themselves are wrong.
A lot can be done with stock jets (and we have better fuel in the UK, I think that helps)
What model of DCOE do you have and what spec is your engine?

Get an STE synchrometer first - the cheapo gunson things are just rubbish.
My hole was only necessary as two barrels on the same carb were different.
I was nervous but Keith talked me into it - thankfully.
It was easy to do and easy to fill in with epoxy if it doesn't work.

Get the float at 25mm too and set the idle mix - still doable without an AFR.
Whilst you are there make sure your floats, and the needle valve they operate, are working correctly and moving freely.

All this is relatively cheap and you learn a lot.
The basics of how the Webers work is not so bad.
We have Keith for the hard stuff!

Simon

[JJDraper]

Carbs are 40DCOE18s, Engine is mildly tweaked with QED 360 cams & big valve spec. QED pistons (not high comp) at +60(!) and Lumenition opto electronic ignition. Head is pretty standard thickness, and the engine runs pretty well on 95Ron fuel at around 10Deg advance (static). Distributor is a 23 D4 in unknown condition, apart from that it works! The dizzy was going to be my next port of call, but I may hold off now. I noted that in Italy it ran better on their high octane 'blue' petrol, but at over 2 Euros a litre, I saved that for special days.. UK fuel seems fine, no pre-ignition at all.

Standard air filter, 32mm intakes, but I can't remember what the jets, are took advice from QED when I fitted the cams.. Air leaks - well I try my best!

Jeremy

[simonknee]

So that is a mildly hot unit you have there Jeremery! It's easy to check what the idle jets are just pop 'em out. According to Miles Wilkins the standard jetting is fine for tunes up to 140bhp so they may well be 50f8. Might as well pop out the main jets and read their spec too (main, emulsion and air). Whilst your at it run the engine for a bit (engine runs without the main jet assembly in), stop the engine then check the depth of the fuel as I did earlier in the thread. If it takes you longer than a minute then run the car again to get the level back up.

You should make sure your dizzy is in good condition since an old unit may be worn and causing spark scatter. Also the advance may not be operating correctly. This can be roughly checked using two people. One to hold the speed at given rpm and the other to check with a strobe - though you do need one of the adjustable timing strobes. You can send your unit to these guys http://www.distributordoctor.com/ (not used them myself). I was never sure about my old 23D4 so I bought an Aldon one http://www.aldonauto.co.uk/shop/product ... 1&P_ID=101 early on in my ownership. Do check that your 23D4 is a 41198 not a 40930 as the later has a completely inappropriate advance curve for anything other than a standard twink (I reckon it's not very appropriate for that either it's just what Lotus got from Lucas at the time!)

Even if there are issues elsewhere there is no reason not to get really fussy with the carb balance or to set the float level to 25mm. With the 40DCOE18 there are no airbleed bypass screws to aid the airflow balancing. Should the barrels in one body prove different then drilling holes is the only way . Should this be necessary you'll have to take the carbs off. So first check that the throttle plates are positioned perfectly and completely fit the barrel when fully closed BEFORE you get handy with the dremel. Shine a torch down the barrel to help you see the gaps.

More questions...

How well does your engine idle? at what rpm? could you balance a mug of tea on it? a glass of wine?
As you increase the revs from idle does the engine get smoother or rougher?
Does it have an off-idle stumble as you first move off?
Are there any rpm where cruising gets all hesitant?
Does it have flat spots in acceleration?
If you go wide open throttle (WOT) are there rpm where this causes it to bog down.
If you lift off the throttle completely do you get snap crack and pop through the exhaust?
Any misfires? Does it spit back through the carbs on occasion?


Simon

[JJDraper]

A quick check on jet shows that the main jets are 125, Emulsion tube F11, Air corrector 170, Idling jet F8 45, and all four are the same.

Idles very well, down to 500 if you want, but this is a little too low when cold, so I set it at around 1000rpm. Starts from cold every time with one pump of the throttle, even with a ?Prince of Darkness? starter. Idles a little low when cold (see above).

Carbs have been set using ?best idle? method. Tends to raise idle when hot, after a run, but this settle down after a while.

Float height last set by me using method in the manual.

Dizzy is the 41198 ? see pic. (PS always take pics when working on the car as they often come in useful, as in this instance). I have seen evidence of scatter using a strobe, so it may have some wear. Possibly the original unit - no idea what the numbers mean..

The car bogs down in many WOT situations below about 2.5-3k rpm (see ?Wot I did in my summer hols? in Free Parking). Running at steady 2-2.5k rpm seems to cause plug fouling ? a pain as this corresponds to around the 50mph speed limit in many areas. It then needs a blast to clear its throat & rev cleanly. A problem when you have been following someone for while & then try to overtake ? WOT causes misfire/stuttering until the plugs clear (I presume) ? plenty of scope for embarrassment. You develop a feel for situations which cause it to bog down & avoid them, so a snap WOT is not something I tend to do.

Off Idle stumble? Not really, more feeling of a lack of power which is made worse by the low gearing. In traffic, the car will trickle along in gear, on idle and take off reasonably smoothly.

Flat spots in acceleration? Again, almost a two stage feel; sluggish below 2-3k, smooth power after 3k, all the way to red line & rev limiter.

Spit backs? A few at idle when cold. Occasional slight snuffle/spit on lagging throttle on the overrun.

No pops or bangs through exhaust on lift off at any rpm. No misfires, apart from extended slow running as described above.

Maybe I?ll include the dizzy in the work ahead!

Jeremy

[simonknee]

Since your idling is good you must have a pretty good airflow balance.
The STE device lets you check balance at higher rpm too.
Better to have perfect balance at 2-3k and suffer a little imbalance at idle.

I'd get that float level to 25mm if I were you, this may well cure your bogging woes.
Plus I'd treat it to a replacement distributor or get that old fella inspected and rebuilt.

Simon

[Galwaylotus]

Jeremy's car's symptoms are similar to my S3 SE's. The main difference is that my engine doesn't like to idle that low. My hypojets and E-tubes are being posted to me tomorrow!
Is the 25mm fuel dimension from the base of the float bowl to the surface of the fuel?