Tune day for Webers

[simonknee]

No not with me, I have not experienced any of his hypojets or O-tubes yet. However it has only been this year that he has finally honed in on what he has been heading towards for quite some time. I personally get the feeling that a lot of his work has been necessary due to the terrible fuel that they have to suffer in the US. We seem to have some better options in the UK what V-Power and other high(er) octane variants. Over there it appears mandatory to have 10% or more ethanol in your juice.

I am on the verge of ordering some up of his bits so will report as and when I do and what the results are.

However I have to say that you can do wonders with his white paper and the stock jetting here in the UK.
You need everything else in good working order.
I have a nice fresh Wilkins engine warmed up to S/E spec.
My ignition is in fine fettle with a new dizzy and pertronix Ignitor II bits.
My carbs don't allow for bypass adjustment, which is a shame, but with the help of a decent sychrometer I had the confidence to drill a 1mm hole in the #4 butterfly. I now have a lovely balanced carbs and probably by luck rather than judgement no off idle stumble.
I also made a few extra mods to stop fuel pissing out of the trumpets which helps things especially given the 25mm float settings.

In the lower revs my AFR really does centre around 12.5. I don't have any flat spots. However it gets a bit richer the other side of 4000rpm as the main jets take over. This is where I believe Keiths O-tubes will help. I think I will start with these and then go for his hypo-jets later.

Simon

[Chancer]

I spent probably 100's of hours tuning and tweaking DCOE's, my Elan has Strombergs but I do have a spare weber engine so may one day tinker again.

I would be interested to read the white paper just to get the brain cells working again, a lot of the knowledge that I had which I hope is still in my brain somewhere was self taught and intuitive, the sort of thing that is very hard to explain to pass on to others, I saw a French friend who is the guru for air cooled racing Panhards setting up twin carbs and doing a dizzy swing by ear, i could tell that he was doing it exactly as I did/do, he also was self taught and could not really explain to someone how exactly he does it.

How does one access the white paper?

[simonknee]

Join up with Keiths yahoo group at:

http://autos.groups.yahoo.com/group/sidedraft_central/

Look in the files section for the white paper.

BTW. A recent thread there shows Keith threatening the long awaited sequel to his original paper. For people that are wondering about his hypo-jets and O-tubes I think this will likely explain all and perhaps remove the need to spend several weeks reading the yahoo forum posts!

[SJ Lambert]

............... no air/fuel ratio cheers
Rohan

Hi Rohan - do you use an air fuel ratio analyser in setting up your race motors?

[Craven]

Hi Simon,
Fuel mixture at high RPM is controlled to a greater extent by the Air Correction jets, try larger size jets.
Ron.

[rgh0]

............... no air/fuel ratio cheers
Rohan

Hi Rohan - do you use an air fuel ratio analyser in setting up your race motors?

I have done all the setup on dynos up to now. I recently bought a AFR analyser but yet to find time to weld the bung onto the exhausts of my 3 Lotus. Even after i do that if I make major engine tune changes I will probably put it back on the dyno once I have it roughly right. Hard to test at 200kmh, 8500 rpm and full throttle on the road

cheers
Rohan

[SJ Lambert]

Any good dyno operators in your neck of the woods?

[lotocone]

Regarding the hypojets that Keith sold, does anyone know how to lean them out ? There are 4 settings for lining up the holes in the 2 parts of the hypojets. I don't have the instructions from Keith's Yahoo group which has moved somewhere else.

Thanks for any help.
Bob

[rgh0]

:D Any good dyno operators in your neck of the woods?

There is a good Weber / dyno guy in Dandenong. He knows race Twin cams well. Google
Bits of Italy

cheers
ROHAN

[mbell]

Regarding the hypojets that Keith sold, does anyone know how to lean them out ? There are 4 settings for lining up the holes in the 2 parts of the hypojets. I don't have the instructions from Keith's Yahoo group which has moved somewhere else.

As I understand it is not quite as simple as one way lean the other rich. They effect idle mixture and low running mixture differently.

I forget which way around it is, but one end will be rich idle and leaner as rpm rise. The other will be leaner idle and richer as rpm rise.

As idle mixture can be controlled what your really running for it to avoid an off idle and transition stumble.

I don't it by just messing around until it drives nice with no stumbling. But plan to do more fine tuning with afr logging when I get to it.

[mbell]

I remember I stashed a way a post on tuning Hypojets (original versions) on my computer.

Source: http://autos.groups.yahoo.com/group/sid ... ssage/4630
-----

This initial run of Hypojets is tailored for folks that DO NOT have a wideband AFM. The step sizes of the adjustments are on the coarser side so it'll be easier to tune by the seat-of-the-pants method. If this is successful I can supply ones later on with finer adjusts to squeeze out the optimal fuel mileage but you'll need an AFM to do it.

First is a warning to not overtighten the Hypojets when installing them into the carburetor, they can be crushed. A torque of one pound per inch is plenty. If you just grab the screwdriver between your thumb and forefinger that will limit the amount of torque to be about the right value.

The easiest approach to tuning the idle/transition circuit is to start on the lean side and move in the fatter direction incrementally until all the misfiring and partial misfiring behavior subsides. When it's really way too lean you'll be able to tell by just elevating the rpms using the idle speed screw(ISS). As the mixture gets closer to the ideal you'll need to drive the car to test the tractability.

Even with a too lean Hypojet there is usually enough fuel being supplied so it can be tuned to idle to perfection. Go ahead and set the idling mixture with each idle mixture screw(IMS). The newer DCOEs use a finer pitch thread on the IMS so about three turns from closed is required. The early carbs with the coarser thread will need about one to one and a half turns.

The Hypojet is comprised of two components which when slipped together are a completed assembly. There is an outer brass jacket that looks like a stock jet but it has four different sizes of air holes spaced 90 degrees apart. The jacket is universal and works in conjunction with every size of the other component which is the insert. The insert carries a piece of hypodermic tubing and there is a variety of tubing sizes to choose from. There is a chart that depicts the size of the tubing via a barcode system of grooves. To add more fuel overall one needs to use a larger inner diameter tubing. The insert has an oversized air hole bleed hole. To make an adjustment to the amount of air passing through the Hypojet the insert is rotated so it's air hole lines up with one of the four air holes in the jacket. The Hypojet is designed so that when the assembly is tightened into the carburetor the insert is loaded and therefore captured so it cannot rotate out of alignment.

Here's how a Hypojet works. Again the inner diameter of the hypodermic tubing is the main means to control the overall amount of fuel flow. The air adjustment allows some leeway to control when that fuel gets delivered. The general rule is the smaller the air hole, the more fuel will be delivered when coming off idle but at the other end of the dynamic range of the transition circuit it will run leaner. A larger air hole will have exactly the opposite effect. It sort of acts like a teeter totter so you have the ability to tilt more or less fuel to where and when you need it.

Be forewarned that if you already have a serious off-idle stumble the Hypojets will likely not cure that problem. That requires the position of the butterfly relative to the first progressive hole be altered.
-Keith Franck

[lotocone]

Thank you very much mbell ! Some of this info is coming back to me now that I can read it again. A friend bought my Elan with hypojets installed and now I'm trying to explain how to make adjustments with them.

[Flying Banana]

Has anyone managed to log their progress with various jets/tubes/air correctors, etc with a wide band AFR which can capture data?

In my view achieving an AFR from around high 12s to low 13s under load at high rpm is the aim. Higher (leaner) AFRs under less load aren't as critical as cylinder pressures aren't as high, so less chance of piston damage. I've gone down this route with my Alfa 105 and have achieved great results.

With a set of jet drills and a soldering iron, it's very easy to experiment with the emulsion tubes in terms of the number, size and height of the holes in the tubes. With logged AFR data (AFR vs RPM, where RPM is a proxy for load) you then have objective data to see the effects of each change. I'm not sure how you can effectively tune a carb without this information?

[digdug]

It appears this group has moved to
https://vintagetechnologygarage.groups.io/g/sidedraft