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Weber/Dell Tuning

PostPosted: Fri Aug 12, 2005 2:30 pm
by "denicholls2"
I can't post on LotusElan.net, probably because I never registered
for it, but I forget.

Three items on the rolling road tuner posting:

1. If your account is accurate, any shop that wastes your time like
that and still takes any of your money needs to be very publicly
exposed. People need to know to avoid it. This would hinge on
whether you were very clear your carbs were Dells and not Webers.

2. For your hour, you should have gotten a printout showing your AF
ratio throughout the rev range of the dyno test. In my experience,
this is 3000 to redline, and includes the progression from idle to
main. Your distribution along this progression is important
information for tuning, although it is almost surely the case you
need to attend to idle jets first.

3. On Webers, and I'm almost certain Dells as well, the jet number
is its diameter. For a fuel jet, larger is richer. For an air
corrector, larger is leaner. Given your current status, I don't see
any reason to borrow a 58 jet.

If you go to the Europa Yahoo site, you'll find in the archives some
excellent Weber advice which I'm pretty sure is the same for Dells.
I used it to straighten out my Europa's 45DCOE, which was fuel
starved at the top of the idle progression (steady-state highway
speed) by a too-small idle jet.

The other piece of input I have is that air correctors have a small
impact relative to fuel jets. You should be able to get your rich
condition straight with just the right fuel jets. The air correctors
are fine tuning in my understanding; your problem is very coarse.

The Haynes Weber book is a valuable tool, also covering Dells. Get
one. It also covers Strombergs and SUs.

I know nothing about tuning the Twincam, but I'm surprised at your
jet sizes. A 1565 Europa Renault runs on a single 45DCOE with 45F8
jets stock (I'm running 50F8) Your setup is permitting twice the
fuel through the idle jets on about the same displacement for maybe
20% more horsepower if your engine is near-stock. That just doesn't
seem right, and jives with a very rich mixture.

I've found that if you have a good feel for the engine's happiness at
various rev levels, and understand the progression circuit, you can
do very well with drive-and-fiddle by yourself. The extra carb will
complicate this a bit, and you MUST have a good method of
synchronization, which can be your ear if it's a good one.

If your tuner is trying to make you buy all the fiddling hardware
anyway, I'd wait to hit the rolling road again until after you think
you've got it about right. The real value of a professional tuner
should be that he has all the tuning bits and only charges for the
ones you wind up with, and can do the job faster than you because of
his experience. You can get there; just remember to chart your
changes along the way so you can get back to safe running if you
stray too far. The joy of the Weber design is how easy it is to make
major jetting changes in minutes. The minor headache is the wide
degree of configurability, which is baffling only if you don't do
things in an orderly manner.

Doug Nicholls, 54/1822

Weber/Dell Tuning

PostPosted: Fri Aug 12, 2005 2:52 pm
by lotuselan2
Doug

I think there is one difference between Weber and Dell jet designation.
Weber number relates to diameter and Dell number relates to flow (probably
at some standard conditions). So with Dell's flow change is proportional to
number change but with Webers flow changes as the square of the
number/diameter. For one size changes it hardly matters but for large
changes or pre-tuning calculations it will.



Posters, am I correct on this?



Ken

'69 Lotus Elan +2 with BDR

_____

From: ***@***.***lto:***@***.*** Behalf
Of denicholls2
Sent: Friday, August 12, 2005 10:30 AM
To: ***@***.***
Subject: [LotusElan.net] Weber/Dell Tuning



I can't post on LotusElan.net, probably because I never registered
for it, but I forget.

Three items on the rolling road tuner posting:

1. If your account is accurate, any shop that wastes your time like
that and still takes any of your money needs to be very publicly
exposed. People need to know to avoid it. This would hinge on
whether you were very clear your carbs were Dells and not Webers.

2. For your hour, you should have gotten a printout showing your AF
ratio throughout the rev range of the dyno test. In my experience,
this is 3000 to redline, and includes the progression from idle to
main. Your distribution along this progression is important
information for tuning, although it is almost surely the case you
need to attend to idle jets first.

3. On Webers, and I'm almost certain Dells as well, the jet number
is its diameter. For a fuel jet, larger is richer. For an air
corrector, larger is leaner. Given your current status, I don't see
any reason to borrow a 58 jet.

If you go to the Europa Yahoo site, you'll find in the archives some
excellent Weber advice which I'm pretty sure is the same for Dells.
I used it to straighten out my Europa's 45DCOE, which was fuel
starved at the top of the idle progression (steady-state highway
speed) by a too-small idle jet.

The other piece of input I have is that air correctors have a small
impact relative to fuel jets. You should be able to get your rich
condition straight with just the right fuel jets. The air correctors
are fine tuning in my understanding; your problem is very coarse.

The Haynes Weber book is a valuable tool, also covering Dells. Get
one. It also covers Strombergs and SUs.

I know nothing about tuning the Twincam, but I'm surprised at your
jet sizes. A 1565 Europa Renault runs on a single 45DCOE with 45F8
jets stock (I'm running 50F8) Your setup is permitting twice the
fuel through the idle jets on about the same displacement for maybe
20% more horsepower if your engine is near-stock. That just doesn't
seem right, and jives with a very rich mixture.

I've found that if you have a good feel for the engine's happiness at
various rev levels, and understand the progression circuit, you can
do very well with drive-and-fiddle by yourself. The extra carb will
complicate this a bit, and you MUST have a good method of
synchronization, which can be your ear if it's a good one.

If your tuner is trying to make you buy all the fiddling hardware
anyway, I'd wait to hit the rolling road again until after you think
you've got it about right. The real value of a professional tuner
should be that he has all the tuning bits and only charges for the
ones you wind up with, and can do the job faster than you because of
his experience. You can get there; just remember to chart your
changes along the way so you can get back to safe running if you
stray too far. The joy of the Weber design is how easy it is to make
major jetting changes in minutes. The minor headache is the wide
degree of configurability, which is baffling only if you don't do
things in an orderly manner.

Doug Nicholls, 54/1822








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Weber/Dell Tuning

PostPosted: Fri Aug 12, 2005 3:53 pm
by twincamracing
well put Doug,

FWIW the 40DHLA used on the 1600 Alfa is jetted as follows:
30mm choke, 120 main, 200 air, 48 idle, 33 pump jet

may prove to be a good base line for your twink, interesting to note
the 1750 went to a 32mm choke and 135 main, other jetting the same and
the 2000 bumped idle only to 50

the dells are as easy to tune as a weber. the jets are all right on top
for quick tuning changes. just need a good baseline to start

i had a similar problem on a Alfa Super, sometimes you need a sedan ;)
where a DPO had installed a pair of 40mm dells to replace the "worn
out" webers and they were jetted for a 2 litre engine

anyway, check the idle jet holder orfices are free and clear, then
check the idle mixture screws 1 1/2 to 2 turns out is about right buit
you may find a bit less than that works better with the bigger jets

the previous question "what are hydrocarbons" these are the unburned
fuel particles after the combustion process, interesting to note 100%
combustion efficiency still has hydrocarbons present as the mixture
between the top ring and the piston crown doesn't get burned. the CO is
carbon oxide, a byproduct of combustion and i should think 2% would be
fine, less than that is heading toward a leaner burn emissions reducing
value

i would think a good rolling road facility would offer a five gas
analysis not just two. here's a write up on five gas analysis:
http://www.smogsite.com/articles.html

cheers,
Scott
+2S

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