Question about DVDA dizzy and Solex PDSIT 34 on Bus
aggri1 - May 23rd, 2007 at 02:38 PM
Quickie:
should a bog stock 1800 Type IV have a dual vac' dizzy? I don't think I've ever seen one, but they refer to them on theSamba.
http://www.thesamba.com/vw/forum/viewtopic.php?t=64533
Was it perhaps a US-thing, emissions-related maybe?
Also if someone can be bothered, what's the function of the flat, electrically-connected thing on the side of the 'main' Solex PDSIT 34 carby,
above the idle cutoff solenoid? It's not labelled on the image in the above-linked Samba thread, and not even present on the photos at the ratwell
dual-carb tuning page: http://www.ratwell.com/technical/DualCarbs.html. Makes a rattle when you shake it.
Mine is disconnected, and the car likes to stall off idle, and stutters at anything below about 2500RPM, and I'm wondering if it's related to this
little thing. It's not connected because earlier I never had the idle-cut-off (called "pilot cutoff" on ratwell) on the main carby, and earlier
the car was easy to drive, no stupid stalling/stuttering. I presume the dizzy's vac-advance is functioning because as I said it ran fine (smoothly)
on the old carbies. Now when I disconnect the wire to the idle-cut-off ("pilot cutoff") at idle, the engine stops. It's wet, so I don't want to
just take it off and leak fuel.
Sorry I know that the above makes little sense, but, aaargh, I am never again buying a dual-carbe'd vehicle! And now I have two such.
Thanks guys,
A.
barenyisbeetle - May 23rd, 2007 at 07:11 PM
this little device functions as a fuel compensator on a hot engine.
It has a thermatic switch (element) that opens an closes at hot temp to supplement fuel to the carby.
Most I have see have been clogged with gunk, in addition to perished seals interfaced to the main carb body leaking fuel. Most have had the passage
too this blocked.
This is overly complicated and as it is old it is probably worn out. make sure it is and that the junction of the wire loop from the cut off solinoid
to this thing is sound.
greedy53 - May 23rd, 2007 at 08:23 PM
duel vac issy i have only ever seen 1 and that was for a supercharger and when the pressure rose in the manafold it would start to advance the dissy
for the blower that sall i can tell ya
kombidaze - May 25th, 2007 at 07:24 PM
on the duel vaccum dizzy the outlet tube on the can that points in the direction of the dizzy is the retard side the other one that points up in the
air is the advance it usually connects to the vaccum outlet on the left hand side carbie, the retard outlet on the vacum can just plug it up. the
other thing you have to do is check all your vacuum lines they run between the inlet manifolds lots of bits of rubber usually old and cracked if they
leak they will definetely upset your idle also the rubber elbows on the outside of each inlet manifold down low they supply a vacuum signal to the
brake booster they leak and can be cracked if so fix em up or your idle will be rough. you can make the solex carbies work good but it does take a bit
of effort, personally i strip em if the throttle shafts are loose i get em rebushed put a gasket kit through em throw away the chokes or disconnect
them make sure the idle cut off solenoids are in good condition or replace them with jets which arfe available just ask vintage or classic or any good
vw mechanic there is a big solenoid at the rear of the left hand carbie its usually stuffed if it is plug up the hole with a bolt then tune and sync
the carbies as per ratwell they should run fine.
aggri1 - May 27th, 2007 at 11:58 AM
Hmmm, thanks kombidaze.
I've replaced all of the vacuum lines including the brake booster elbows. I had the carbies re-bushed, cleaned and surfaced. I put in new gaskets
and diaphragms, new needle valves (one old one was intermittently sticky). Had the carbies balanced and 'tuned' at a garage - I haven't got a
Unisyn nor CO meter. I'm rather disappointed in the result. Very hard to drive.
Ah well, I'll keep looking.
Cheers, a.
ratty 63 - May 31st, 2007 at 09:57 PM
Ahhh, EFI.... Oh, did I just say that out loud? 
R 
aggri1 - June 1st, 2007 at 08:04 AM
| Quote: |
Originally
posted by ratty 63
Ahhh, EFI.... Oh, did I just say that out loud?
R
|
Dude, guess what I just spent a lot of time reading about yesterday! Haha, I now really want to try it (FI that is), because it doesn't sound that
complicated really. I will start hunting down the stuff I need... including an FI fuel tank, which is the biggest thing yeah?
Busses used L-jet didn't they?
One thing I wasn't clear on was this; in K-jet and L-jet, all injectors squirt simultaneously right (continuously in K-jet!)? (Did I understand that
wrong?) But, of course only one cylinder is sucking in air at any given moment, so presumably the squirted fuel just sits behind the inlet valves in
the other three, until it's their turns to ingest air. Now I don't know if that's quite how it works, maybe I sound like a dumbass, but I've
never had an FI car of any kind - I need to have a look at some FI injectors & manifolds & heads & stuff I think, to see exactly how it should
function (I like to know how stuff works, being an unjineer and all). They're not direct injection into the combusion chamber are they?
Are FI TypeIV heads different to carbies ones? I wouldn't have thought so, perhaps with the exception of some drilling for the cyl head temp
sensor.
Cheers, A.
ratty 63 - June 3rd, 2007 at 09:56 PM
| Quote: |
Originally
posted by aggri1
Dude, guess what I just spent a lot of time reading about yesterday! Haha, I now really want to try it (FI that is), because it doesn't sound that
complicated really.
|
Hehehe, I too decided to look at EFI when I got tired of fiddling with carbies which just were not able to do the job. EFI really isn’t all that
complex once you have a basic understanding of how an EFI system works
| Quote: |
Originally
posted by aggri1
I will start hunting down the stuff I need... including an FI fuel tank, which is the biggest thing yeah?
|
An EFI fuel tank would be the best and neatest way to install EFI – and you have the advantage of owning a vehicle that came out on the Australian
market with EFI fitted from factory (I did my conversion to a Beetle so had to sort out my own tank), so the parts do exist. The other option is to
run a separate surge tank, but this will then require mounting somewhere under the vehicle, and the existing fuel tank still has to be modified to
accept a return line… Stick with search for a factory EFI tank!
| Quote: |
Originally
posted by aggri1
Busses used L-jet didn't they?
|
As far as I know – perhaps someone else can confirm this for us…?
My EFI system is made up of bits from the good old Holden Camira, but the principal of operation is still the same. My Brother has an EFI Bay window
Kombi that he is currently cleaning up after an engine fire (he purchased it in this condition) – he will be rebuilding the EFI system from parts
that he has collected over the years and refitting it – perhaps, if I get enough time I can cover this in another post or on my website….
| Quote: |
Originally
posted by aggri1
One thing I wasn't clear on was this; in K-jet and L-jet, all injectors squirt simultaneously right (continuously in K-jet!)? (Did I understand that
wrong?) But, of course only one cylinder is sucking in air at any given moment, so presumably the squirted fuel just sits behind the inlet valves in
the other three, until it's their turns to ingest air.
|
Yep, yep and yep. Mechanical Injection systems (like the type fitted to the early Porsche, and Audis) squirt continuously, the fuel pressure changes,
which (obviously) changes the amount of fuel that is delivered.
Early EFI systems, such as the ones fitted to the Kombis and Type III’s (and most production cars up until the mid-to-late 80’s and even some
cheap 90’s cars too) are “Batch fire” systems. They fire all the injectors simultaneously, and the fuel just sits behind the valves until they
open. These systems require the injector to be fired 4 times (on a 4 cylinder) for each cylinder to receive the correct amount of fuel (six injector
fires for a six cylinder, etc)
Late model EFI systems use a cam angle sensor to tell the ECU which cylinder is about to fire and the ECU will only open the corresponding injector
(although rumour has it that this is only the case at low revs). This style of injection is known as “Sequential” injection.
There is much argument about the benefit of sequential injection versus the hassles of installing and wiring a cam angle sensor. Some argue that
Sequential is smoother and more economical at low revs, whilst other say that this can only be seen on a Dyno and most people would never notice the
difference on the road… the argument still rages…. I personally find that batch injection works just fine for me!
| Quote: |
Originally
posted by aggri1
Now I don't know if that's quite how it works, maybe I sound like a dumbass, but I've never had an FI car of any kind - I need to have a look at
some FI injectors & manifolds & heads & stuff I think, to see exactly how it should function (I like to know how stuff works, being an unjineer and
all). They're not direct injection into the combusion chamber are they?
Are FI TypeIV heads different to carbies ones? I wouldn't have thought so, perhaps with the exception of some drilling for the cyl head temp
sensor.
|
No they don’t inject directly into the head, it all goes into the manifold, just above the intake port (in most cases – as certainly in the case
of the factory systems).
There should not be any differences between the heads on an EFI engine and a carb’d engine – as far as I know all the type IV heads have the
fitting beside the intake ports for the Temp sensor (referred to as Temp Sensor II in the factory manuals). All the other sensors are mounted on the
manifold. I know that some of the twin port Type I heads even had the mounting point for the temp sensor. It would be wise to have a quick look at
yours just in case – if it were me, I would have the only set in existence that do not have the temp sensor mounting point!
Good luck with this – it will be a steep learning curve initially, but I can honestly say that it is very unlikely that I will ever own another
Carb’d car – EFI is just SOOO much better.
Cheers,
R
aggri1 - June 3rd, 2007 at 10:49 PM
Cool, thanks for the response. I am hoping to come up with a stock Bus FI system rather than Camira (or other aftermarket) bits.
Cheers, A.
ratty 63 - June 3rd, 2007 at 11:03 PM
Yep, good idea.
I know that my Brother (Dave) has found a number of complete (or very close to complete) systems at swaps - all at very low prices. May be a good
idea to get a couple of systems so that you can pick out the best bits to make one complete system.
R
aggri1 - June 4th, 2007 at 11:31 AM
Hey, Ratwell says
| Quote: |
A healthy stock vw
engine at idle normally reads 15-18" of vacuum but that reading depends on the timing (advance vs. retard) and the altitude you are taking the
reading at.
|
Now obviously there must be some assumed fluid he's talking about and he means manometer height, because vacuum is a pressure and doesn't have units
of length. Anyway, does he mean water or mercury (or something else)? I am guessing water, but I thought I'd check with you guys.
With water, 17" is about 4.2kPa. Sound right?
Any differences expected between type1 (single carb/long inlet manifold) and typeIV (twin carb/short manifold)?
Cheers, A
EDIT: link to Ratwell: http://www.ratwell.com/technical/FAQ/FAQContent.html
[ Edited on 4-6-07 by aggri1 ]
ctefeh - June 4th, 2007 at 04:52 PM
Aggri1,
The reference is in/Hg. I.e. 15-18 inches of mercury at idle. Standard imperial measurement unit for vacuum.
Ctefeh.
aggri1 - June 4th, 2007 at 06:03 PM
Mercury! Density of Hg is 5,427 kg/m3, meaning that the inlet manifold vacuum would infact be around 4.2kPa * 5,427kg/m3 / 1.000kg/m3 = 22.8kPa.
Gosh.
Thanks dude, A.
EDIT: must've stuffed something up. I get 17" Hg = 57,568Pa with a unit converter (on the computer).
[ Edited on 5-6-07 by aggri1 ]