From: Noddy on

"John McKenzie" <jmac_melbourne(a)bigpond.com> wrote in message
news:4749B65C.5C8C(a)bigpond.com...

> Based on everything so far - it's the twin spud setup not being
> compatible with a two barrel that has different primary and secondary
> opening rates. I definitely think the amos ring/ carb hat device is the
> best option - it will not be bothered at all by the secondary opening
> rate - since it sits above the top of the carb. It's also 100%
> compatible with the current convertor - so there'd be little work to do
> to actually fit it.

I agree.

It'd be the cheapest and easiest work-around to getting the thing running
properly.

--
Regards,
Noddy.


From: Noddy on

"Yvan" <me(a)privacy.net> wrote in message
news:5qu355Fqb3seU4(a)mid.individual.net...

> It's a mixer plate with one ring over both barrels. It might not be
> clear what I vanted to say looking at my artistic visualisation :-)

I got the idea :)

If you're going to fabricate your own basic mixer, which isn't terribly
dificult, there's two things you need to bear in mind if you want it to be
successful. It needs to be designed in such a way that the air will flow
past the gas entry point and draw the gas into the engine, and it has to be
capable of flowing as much air as the carburettor is at the minimum
otherwise it will cause a restriction and reduce performance.

Here's some detailed photo's of my Amos mixer that may help you get a better
idea of things:

The mixer as fitted to the air filter housing in it's standard working
position :

http://i31.photobucket.com/albums/c389/dasgib/100_3353.jpg
http://i31.photobucket.com/albums/c389/dasgib/100_3354.jpg

The mixer on it's own:

http://i31.photobucket.com/albums/c389/dasgib/100_3357.jpg
http://i31.photobucket.com/albums/c389/dasgib/100_3360.jpg
http://i31.photobucket.com/albums/c389/dasgib/100_3359.jpg
http://i31.photobucket.com/albums/c389/dasgib/100_3358.jpg

And finally, the mixer's position relative to the carburettor when fitted,
without the air filter housing for clarity:

http://i31.photobucket.com/albums/c389/dasgib/100_3363.jpg
http://i31.photobucket.com/albums/c389/dasgib/100_3364.jpg

The mixer's dimensions are roughly 200mm in length, by 120mm in width at the
widest part of the "mouth", by 50mm in height. The air filter bolt spacing
of the Weber it was fitted to is identical to yours, so one of these things
should bolt straight on if your air filter housing will allow enough
clearance.

The shape of the thing isn't overly important, although it plays a part, as
the mixer's shape is largely influenced by the shape of the air filter
housing it's designed to fit into. The wide "funnel" shaped mouth is the
most important part of the whole device, as that tends to act like a venturi
right at the point where the gas is introduced into the airflow.

What is probably most important is the position of the gas entry point
relative to the top of the carburetor, and the arrangement of the gas entry
pipe with regards to it's shape and angle. It's positioned in such a way as
to provide a good vacuum signal on the vapor line without causing a masive
airflow restriction. It is imperative that the mixer is effectively sealed
against the air filter housing at it's base so it doesn't draw air through
anywhere other than the mouth, as this will dramatically effect it's ability
to provide a good vapor line signal.

This particular arrangement worked reasonably well on a 4 litre 6 cylinder
engine once the automatic choke was converted to manual operation so the
thing would start easily on lpg. It ran a single vapor line from the
converter up through a hole drilled into the bottom of the air filter
housing and onto the mixer with a standard single adjuster in the line and
the engine was tuned to provide the best wide open throttle performance with
the gas idle set with the engine cold. It would start easily in cold weather
(admittedly winter in Melbourne isn't anywhere near as cold as where you are
I expect), had a smooth idle and would deliver adequate performance.

It didn't provide optimum performance for the engine it was fitted to, but
as John quite rightly pointed out that's mostly due to the carburettor being
inadequate for the size of the engine. However, it performed very reliably
and would most likely work very well indeed on your engine. If used in
conjunction with a variable adjuster it would be a good system.

http://www.tinleytech.co.uk/kit-extras.html#Lambda%20control

--
Regards,
Noddy.






From: John McKenzie on
Yvan wrote:
>
> Nedavno John McKenzie piše:
>
> >> BTW I also have another problem. Engine will not run on lpg until it
> >> heats up around 1/4 of the normal operating temperature, and will
> >> stall if I lift my foot of throttle. When it heats up it runs OK at
> >> idle.
> >
> > Ok the 'theory' on this is that you are supposed to set the idle a/f
> > mixture when the motor is cold for best cold idle smoothness. What is
> > supposed to happen is that as the car heats up, the higher coolant
> > temperature flowing through the convetor will automatically lean the
> > mixture out a little bit to suit.
> >
> > That's basically where I'd be looking to fix it - by starting it, and
> > adjusting the idle a/f till it will run when completely cold. It might
> > need another person there to help start and help keep it running
> > whilst you adjust the mixture.
>
> But if I turn idle setup mixture screw more than half a turn in or out
> while engine is hot revs will drop, and I think that it may need more
> than half a turn to get cold smooth idle.
>
> Than again, I now disconnected lpg hose to the second barrel, and I
> think I have better setup now, so I am going to try this tomorrow.
>
> >> Before I changed carburetor I could start my engine on lpg. Just to
> >> mention it runs OK on petrol.
> >
> > Based on everything so far - it's the twin spud setup not being
> > compatible with a two barrel that has different primary and secondary
> > opening rates. I definitely think the amos ring/ carb hat device is
> > the best option - it will not be bothered at all by the secondary
> > opening rate - since it sits above the top of the carb. It's also 100%
> > compatible with the current convertor - so there'd be little work to
> > do to actually fit it.
>
> I have never seen this carb hat before. Can you post a link to a page
> with more details of it's design?
>
> What do you think about this:
>
> http://www.ptt.yu/korisnici/i/v/ivica/lpg/MixerPlateIdea1.jpg

That's more or less all that is required - and it's what many of them
look like. The one on local early 80s commodores (similar to an Opel
Rekord in Europe, with an Australian made engine, and a rochester
varijet carb) looks very much like it.

It doesn't have to look like a venturi - as long as the critical
diameter is about right for the flow, it will accelerate flow at the
critical point and provide a signal for lpg to flow.

The trick is to run with a hole size that gets you good throttle
response for normal driving, but isn't so small it acts as a huge
restriction from mid range rpms and above.

More than a few lpg setups actually suffer from that, which is the real
cause of any significant power losses on lpg (anything more than about
5% losses is not due to the fuel type, it's due to the setup itself)

I've drawn where the 'feeds' could go to suit yours. If possible - run
two - one on each side. I've drawn two different ones. The best is to
have them as wide as possible to expose them to more of the pressure
drop created by the 'venturi' of the amos ring/carb bonnet (it's
probably got a few different names elsewhere too). So running two like
the top one would be best. If the only one you can get/make is a little
thinner it will still work.

If, no matter what you do with idle and full speed mixture, the setup
didn't have any throttle response, then there's two main options left.

The first one is a little more time consuming - but I assure you it _is_
something that can be done with a small amount of tools. The fix
involves re-curving the distributor to suit lpg. If the main fuel used
is lpg, then definitely take advantage of this option. If petrol is used
a lot, you have to compromise on one (unless you go to yet another
option). Basically lpg likes more initial timing than a petrol engine.
There's a couple of reasons for it. One is to do with lpg itself. The
other is because of how lpg convertors/amos rings provide lpg during low
flow/idle/low rpm situations. Simple enough. But it tends to like a
little less total timing. It also tends to like the total timing (which
is a product of the initial setting and the mechanical/centrifugal
advance) to come in a little earlier than for petrol. The problem of
course is there is _already_ more total timing than it needs. So if you
just adjusted the initial timing higher, it would run better down low,
but it'd have twice as much extra timing than it needed up top. So the
distributor has to be altered to provide less mechanical/centrifugal
advance.

It's not the easiest job in the world, but it is definitely doable. I
can give you the method if you need. BUT - first thing I'd check is
whether or not different distributors with different curves were
available for that engine. Maybe there is one you could find in a
wrecked car that would do.

The other option - which is easier to be sure, but not cheaper is to go
to a dual curve ignition. Very basically it is wired into the
distributor/ignition circuit, and it takes a signal from the lpg/petrol
switch too. After it's installed and adjusted, it will automatically
alter the timing to suit which particular fuel it is on. This means that
it will actually give you the benefits on lpg, AND no compromise - the
'right' curve on petrol too. It is a great option for most. I'm not in
that category, since my cars run on lpg only, so I don't need it.

Another thing that is fairly well known is that for lpg engines, a
slightly smaller spark plug gap works better. Generally speaking, if you
close them by 5 thou (.125mm) over the factory specification for petrol,
you will get the best result.

Lastly - if after all that you couldn't get acceptable throttle
response, then the option would be to increase the signal strength of
the venturi. If you used your design, you'd make the circle a little
smaller. On Noddy's, if you use that one, you'd alter it like this
picture (you could tig weld it, or even use some sort of fibreglass
with an extra screw to help secure it.

http://jmacperformance.com/lpg%20stuff/amos%20ring%20shape%20inside.JPG

http://jmacperformance.com/lpg%20stuff/carb%20hat%20venturi%20modification.JPG

http://jmacperformance.com/lpg%20stuff/mixer%20plate%20feeds.JPG

http://jmacperformance.com/lpg%20stuff/mixer%20plate%20feeds2.JPG



--
John McKenzie

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From: Yvan on
Nedavno Noddy piše:

> The mixer's dimensions are roughly 200mm in length, by 120mm in width
> at the widest part of the "mouth", by 50mm in height. The air filter
> bolt spacing of the Weber it was fitted to is identical to yours, so
> one of these things should bolt straight on if your air filter housing
> will allow enough clearance.


Hight is critical. I just measured, and I have 44 mm from the air box
base to the top cover. And that is if I remove top cover fixing nut
carrier.

So 50 mm high amos ring would not fit. Thank you for your kind offer to
send it to me by post. I appreciate that.


--
___ ____
/__/ / \ ** Registrovani korisnik Linuksa #291606 **
/ / \/ /\ \ ** Registered Linux user #291606 **
/__/\____/--\__\ ** http://counter.li.org/ **
From: Yvan on
Nedavno John McKenzie piše:

>> What do you think about this:
>>
>> http://www.ptt.yu/korisnici/i/v/ivica/lpg/MixerPlateIdea1.jpg
>
> That's more or less all that is required - and it's what many of them
> look like.
>
> It doesn't have to look like a venturi - as long as the critical
> diameter is about right for the flow, it will accelerate flow at the
> critical point and provide a signal for lpg to flow.
>
> The trick is to run with a hole size that gets you good throttle
> response for normal driving, but isn't so small it acts as a huge
> restriction from mid range rpms and above.

Venturi for the primary barrel is 22 mm, and for secondary barrel 24 mm.
That is combined area of 832 mm2. So I think that one ring with inside
diameter of 34 mm would be OK. The simplest for fabrication would be to
fix aluminum plate on four bolts on top of the carburetor, and drill a
~50 mm hole in the middle where I will insert a venturi ring like on
this photo:

http://www.ptt.yu/korisnici/i/v/ivica/lpg/mixerplate.jpg


> I've drawn where the 'feeds' could go to suit yours. If possible - run
> two - one on each side. I've drawn two different ones. The best is to
> have them as wide as possible to expose them to more of the pressure
> drop created by the 'venturi' of the amos ring/carb bonnet (it's
> probably got a few different names elsewhere too). So running two like
> the top one would be best. If the only one you can get/make is a
> little thinner it will still work.

Fitting a amos ring/carb bonnet is more difficult because of a tight
space, but I think I could fabricate one. Simple mixer plate would be
easier.

> If, no matter what you do with idle and full speed mixture, the setup
> didn't have any throttle response, then there's two main options left.
>
> The first one is a little more time consuming - but I assure you it
> _is_ something that can be done with a small amount of tools. The fix
> involves re-curving the distributor to suit lpg.


I was thinking about that too. I have Ford EDIS system that I want to
fit to my BMW. I need to fabricate 36-1 trigger wheel, and order
MegaJolt Lite Jr:

http://www.autosportlabs.net

If I get ti to work, I will have option for two switchable ignition
maps. I just wanted to get lpg setup correctly first (at least that I
can start, and run reasonably well on lpg).


> Another thing that is fairly well known is that for lpg engines, a
> slightly smaller spark plug gap works better. Generally speaking, if
> you close them by 5 thou (.125mm) over the factory specification for
> petrol, you will get the best result.


I will check spark plug gap.


> Lastly - if after all that you couldn't get acceptable throttle
> response, then the option would be to increase the signal strength of
> the venturi. If you used your design, you'd make the circle a little
> smaller. On Noddy's, if you use that one, you'd alter it like this
> picture (you could tig weld it, or even use some sort of fibreglass
> with an extra screw to help secure it.


I think that my design would be easier for experimenting, I just have to
put a ring with different inside diameter in existing plate.


--
___ ____
/__/ / \ ** Registrovani korisnik Linuksa #291606 **
/ / \/ /\ \ ** Registered Linux user #291606 **
/__/\____/--\__\ ** http://counter.li.org/ **