HypoJets and O-tubes on the way...

[simonknee]

Many of you will know what I am on about!

For those that don't a one time member of this site has spent 6 years milling small bits of brass into performance enhancing idle jets and emulsion tubes for Weber DCOE. I've just ordered a set.
http://www.webstore.com/82598,owner_id,other_items

This is mostly prompted by the fact I have finally got my LM-2 working properly:
http://www.innovatemotorsports.com/products/lm2.php

There seemed little point getting obsessive about the DCOE until I could actually measure the changes.
I can now log AFR v RPM v TPS (throttle position) whilst driving and make pretty 3D charts on my laptop afterwards!

I'll post up how I get on with Keith's little babies and the results from the logger too.

P.S. has anybody this side of the pond already got a set?

[simonknee]

Here's what the LM-2 and the Logworks software produce from today's 45 minute drive across London to work.

Firstly a scatter plot which gives a good idea of my state of tune.
The plan is to narrow things up around the 12.5 mark
------------

More detail here by averaging the AFR and mapping this against RPM and TPS
Looks a little rich perhaps but I have included the chart showing number of points for each average.
This shows that the values around the edges do not have enough samples to be worried about.
What you see here is mostly the idlejet performance since I rarely WOT in town!
------------

And for fun this is me driving up Tottenham Court Road.
As my foot goes down (red) you see the effect of the accelerator pumps on the AFR (purple) pushing it rich.
Not enough to bog down plus I am pleased it doesn't lean out badly when I let off.
Keith considers my tune "not bad" for standard bits.

More fun graph related fun to come

[trw99]

Good stuff Simon and thanks for posting. Ish all be interested to see how you get on with Keith's kit.

Tim

[mart2elan]

Hi Simon,
I do have a set on this side of the pond (Netherlands) and on allmost the same settings as your engine (standard SE cam exept for the chokes 33 mm).
I am running Keith's Hypo 0.020" on the thirth air hole and the O3 with a 120 wet jet and the special Hypo 100 dry jets.
Overall it runs great.
Running very smoothly on low throttle untill 2700 RPM and with a fuel mileage of 32 mile/gallon (UK). Before it was 24 mile/gallon.
Even driving 1100 RPM in 4th gear is no problem.
Stepping on the throttle is also much better then before and gives full power to the redline (6800 RPM). I really need a rev limmiter now.
The only (solvable) problem there is left is on cruising speed (55 to 80 MPH). There is a hunting/hesitation between 3000 to 4400 RPM and on these speeds the fuel mileage falls down to 24 miles/gallon. On my TPS signal this occurs between 7% to 23% throttle.
Keith already told me what to do (changing the progression holes) but lack off time and the fact that i really want to understand the stuff before i modefy the carb's sets me on hold for the moment.
Your graph's look great. I don't have a AFR meter myself but looking at the graph's i think it's a very good help not only for tuning but also for really understanding these carb's and the efects of changing yets, chokes ect.
Marten

[gjz30075]

Thanks Simon. I'm going to follow this. Been following Keith's forum for a while now, too.

Greg Z

[Jason1]

Hi Simon

I have also been reading your posts on Keith's site as they pop up on my Blackberry.

I can now log AFR v RPM v TPS (throttle position) whilst driving and make pretty 3D charts on my laptop afterwards!

Presumably as your car is a standard non-big valve we would get the same results as you without the need to install the logging equipment? I rarely find time to fix the car and get it back on the road so will be interested in what tubes work well that I could order and pop straight in.

Keep up the good work.

Jason

[simonknee]

I had the engine rebuilt with C-type cams and standard valves when Miles did it a couple of years back so this is straight SE spec. The carbs are currently in factory spec for SE too. To get to the current state of tune I have balanced the flow through the barrels (by drilling a 1mm hole in butterfly #4) and set the float level to 25mm.

I will post full current specs soon.

I anticipate that my limiting factor is also going to be the progression holes in my 40DCOE18 plus the fact that these early units do not have the air bypass adjustment for properly positioning the butterfly regarding the first progression hole. But I'm not stumping up for a new pair of 40DCOE-152 until I have to!

Next step is to do a proper fettle of my current setup have since I haven't checked the carbs since last summer!
I'll take some pics as I do this.

Keith seems pretty sure that you can tune his latest bits without the AFR.
You may still need to go through a few values of jetting to get it spot on.
I imagine that his next white paper is going to make it all a bit clearer.

Simon

[mart2elan]

Hi Simon,
The spec's of my twink are listed in the database on the sidedraft group (Marten van der Goot)
Looking in the database i see your spec's are there also. Are the still current?

I have the Hypo .020 , .022 , .024 and gone through all of then including the change from O3 to O4 and O5 E-tubes but it didn't cured the problem (hesitation cruising speed).
I'm sure that Keiths jet are top and have nothing to do with this problem.

My carbs are 40DCOE 31 with 3 progression holes. I think Keith is absolutly right and i have to make some changes there.
First i have to solve another problem and perhaps the same (partial) cause for the hesitation at cruising speed.
On idle i can't get the engine below 900 RPM. I have already exchanged the old spindle bearings for double sealed one's and checked all standard causes for air leaks.
I'm pretty sure there are no air leaks in outside boundery of the carbs anymore.
The only possibility left is a misalignment of the throttle plates (to much air in close position) or a bad top gasket where the spindle return spring and the acceleration pushrod are located.
The last one can give an air leak (from the fload chamber) on the unsealed inner spindle bearings.

I'm also looking forward to the next white paper and i hope it helps me to really understand these carbs.
I know an AFR isn't neccesary but i like to see/verify the effect while tuning/changing the carbs (that's just me).
I have seen a nice and not expensive one from Tech Edge. It's a DIY and maybe a nice project for the winter evenings.

Marten

[simonknee]

I think the database is correct except the idle jets - not sure what I currently have in there!

[CBUEB1771]

I have the Hypo .020 , .022 , .024 and gone through all of then including the change from O3 to O4 and O5 E-tubes but it didn't cured the problem (hesitation cruising speed).

Are you sure you don't have a small air leak into the inlet manifold? From time to time I have experienced hesitation at cruising speeds and always found that a Thackeray washer had broken and an o-ring between the carburettor and inlet manifold was not sealing adequately as a result.

[jimj]

Look, I know nothing and I`m just back from the pub so a bit squiffy but, surely, the most important thing is to make sure your carbs. are rebuilt properly, first of all, then have them set up on a rolling road, that`s it.
I appreciate that those with more knowledge get great satisfaction from over-my-head-stuff but what we really want to know is; what do you buy and fit and what gains do you make?
Apologies for the Rioca,
Jim

[StressCraxx]

I have a set of Keith's Hypojets and am very pleased with them. The dreaded flat spot from idle to 3K rpm is gone! I am using the 0.020" hypos. By the seat of the pants, I think we can go leaner, perhaps to 0.018".

Sorry, no data yet. I am looking to pickup a portable AFR meter with datalogging. I tried to get a karting AIM Mychron4 to config with my lambda kit, but no dice.

I have an earlier version of the e-tubes that still need some work, going lean at full throttle at low rpm. Keith has his Elan dialed in really well. We are working to find the right combo for my car and we are close. Plan to raise the float level and try the new ones he gave me this week.

We did a lot of work getting my floats just right, the pivot pins were very worn and needed replacement, plus getting the float levels just right. My son and I ran the memorial rally for vintage racer and vintage rallyist Martin Swig a few weeks ago. My son was very impressed how much better the car ran compared to the last time he drove my Elan with the original Weber jetting.

Regards,
Dan

[simonknee]

A fair, squiffy, point Jim - why mess with something that can be set up perfectly well as Mr. Weber intended - surely the makers of these things knew exactly what they were doing back in the day and most issues that owners have come from worn parts and ill-advised tinkering. CC: "Make the suspension adjustable and they will adjust it wrong -- look what they can do to a Weber carburetor in just a few moments of stupidity with a screwdriver"

Well that's exactly what I will find out and post in this thread. As I now have my logger fitted (constantly measuring AFR, RPM and TPS. I should be able to quantify what gains (or losses) I make.

Years of theory, manufacturer and testing have gone into Keith's custom idle jets and e-tubes.
Fortunately this is reduced to a handful of components you can fit.

I can't wait for them to arrive!

Simon

[StressCraxx]

A fair, squiffy, point Jim - why mess with something that can be set up perfectly well as Mr. Weber intended - surely the makers of these things knew exactly what they were doing back in the day and most issues that owners have come from worn parts and ill-advised tinkering. CC: "Make the suspension adjustable and they will adjust it wrong -- look what they can do to a Weber carburetor in just a few moments of stupidity with a screwdriver"

Well that's exactly what I will find out and post in this thread. As I now have my logger fitted (constantly measuring AFR, RPM and TPS. I should be able to quantify what gains (or losses) I make.

Years of theory, manufacturer and testing have gone into Keith's custom idle jets and e-tubes.
Fortunately this is reduced to a handful of components you can fit.

I can't wait for them to arrive!

Simon

Simon,

Exactly. The carbs themselves have evolved, but the basics of the idle jets and emulsion tubes have changed little over the years. There is always room to improve on a design. We look forward to hearing about your results.

Regards,
Dan

[simonknee]

Let's tune what we've got the Keith Franck way...

The LM-2 kit

You can see the Bosch wideband 02 sensor in it's bung just after my y-pipe. When I am not running the LM-2 unit I can unscrew the sensor and put a blanking screw in. It can damage a sensor to run it without power. (hmm must redo the teflon tape on the gearbox lower bolt)
The TPS (Throttle Position Sensor) is mounted using bits that weber supply with the device. I need some small spacers to mount it a little straighter but it works fine as is. It is a, lightly sprung, rotary pot of about 5K (I think) so the three connections are 5V, GND and Output.

I mentioned before that I used the Speedy Cables RVC conversion circuitry inside the tach to provide a stable 5V for the TPS and a stable pulse for the RPM reading in the logger. The back of the tach also made a handy point to provide a common ground for the system. So of the three cables one goes straight to the O2 sensor to power it and read the output. One gets 12V to power the unit, which I pick up behind the tach. The third has the rpm pulse input and the tps input, again all found behind the tach.

I used an old suction phone holder to mount the LM-2 on the window and I can hang it in reverse for reading the settings whilst under the hood.
This is brilliant as you can instantly see changes in AFR (AIR to Fuel Ratio) and RPM whilst fiddling with the carbs. Plus the RPM is much more accurate than the Smiths gauge.

The float level.

The Keith method is to have the fuel 2mm below the passage way for the auxillary venturi. This equates to 25mm below the deck that the jets screw into.
Best done with the engine running but I find it easier to do it just after it has stopped. Using a night light for a kindle (!) I get a reflection on the surface of the fuel. Lowering a small screwdriver into the hole I can easily see when the surface of the fuel is broken. The addition of a bullet connector sleeve onto the shaft means it records how deep this was like this:

Hmm 26mm, not bad, with keiths +-1mm tolerance and certainly not enough for me to dismantle the carbs to fiddle.
I should probably buy an optical device from Keith but I'm used to this method of mine now.
If you set your float any other way at any other level then you don't know what your missing!!

The Balance

Look at me - four hands! Get yourself one of these nifty STE devices they are brilliant.
This was done at about 1000rpm. It's not bad, all of them are about 4Kg/m3.
Eagle eye'd will notice that number 4 is a bit low.
It used to be really low until I did this:

Down the barrel of number 4, can you see it? Look closely at the lower half of the butterfly.
See the 1mm hole I drilled!
Now if I had more modern DCOE rather than the 18s you see here then the air bypass adjustments could achieve this instead.
As it stands next time I take the carbs off I will enlarge the hole a little.

The Idle
I currently have 45f9 in all the barrels, this is as per spec for 40DCOE18 on a Twink. I have tried the weber alternatives around this value e.g. 45f8, 50f8, 50f9 and none are as well behaved through the transition circuit as the 45f9. The 45f8 were next best but will have to test them again to quantify this.

So ensuring that the idle never goes over 1000rpm I close the mixture screws in turn and mark them with a pen at 6 o'clock. The engine should stumble when any one screw is closed or you have an air leak! I open each up about 1/2 a turn then go back a bit until I find the max rpm (careful of that idle). I find that this max rpm is on a bit of a plateau rather than a peak so I go for the weak end of it on all 4 barrels. This results in an AFR of 16-17. The "best lean idle". All very well but this results in stupidly lean mixtures, above 20, when you are actually driving - especially on the over-run. So as per Keith's wisdom all the barrels are made a bit richer until the LM-2 reads 12.5.

That's it.

So here is the spread of AFR I get. What we are after is as much 12.5 as possible:

Hmm must be careful though. This is a 45min run across town: barely ever WOT, mostly under 3000rpm and lot of idle (traffic lights).
With a lot of idling in the data I am bound to get a 12.5 peak 'cos I set idle at 12.5 earlier!
So I graph across a shorter section of the same run and selected a portion where I was not idling (the rpm and tps data allowed me to do this)

Not as good eh? This is what I hope to improve with Keith's HypoJets.

If I get a chance I will do some more controlled runs at higher speeds but need to get out of town to do this.