Shop4Parts - UK's largest online superstore for FIAT and Alfa Romeo parts

General FZD issues

Currently reading:
General FZD issues

Problems not solved here yet, although they are getting better. Just fitted a No. 3 emulsion tube which helps.

Here's the big question.

Why is my pump plunger jet discharging fuel into the venturi at moderate engine rpm before the main jet comes in AND without accelerator being depressed?
 
A couple of extracts from Des Hammill's excellent book -

"Fit the accelerator pump jet that is the smallest possible compatible with the engine having good acceleration without any hesitation"

... and still talking about the accelerator pump jet

"When the Weber or Dellorto carburettors are full of fuel they will squirt fuel well over 3 feet/1 meter when the throttle is opened quickly"

So yeah, they do squirt rather than atomise. Still doesn't explain why yours are in continuous action though :confused:

I'll take the air filter off mine tomorrow and have a look both with and without the engine running.

Chris
 
Above and beyond Chris, many thanks.

We are getting a better squirt now – annoyingly without having changed anything other than stripping down and re-assembling. But still way too rich.
 
Today we ruled out the possibility of a crack in the body moulding where the pump weight is.

Could be a fault in the overall body moulding though?
 
Another interesting quote but this time from John Passini's book on Webers -

Talking about diaphragm-actuated accelerator pumps -

"The fact that diaphragm pumps are 'quick on the draw' was mentioned earlier. This can give rise to a discharge from the pump jets at idle if the geometry of the throttle linkage is such as to produce a slight - almost imperceptible - movement of the spindle as the engine rocks."

He goes on to say that -

"With piston pumps there is normally sufficient lost motion for this not to occur."

Worth considering as our engines rock quite a bit at idle?

Chris
 
Another interesting point, thanks Chris. The guy at Eurocarb commented that there's was a lot of vibration on my video. I'll look into this too.
 
Tim:- Have you made your new (correct length) accelerator-pump actuating rod yet? If you need to know what the measurements are for each of the sections on the rod, let me know and I will get them for you. I think that it is important that you get that rod the correct length---your original is way too short.
Chris:- When I was at Radbourne Racing I met John Passini a lot of times--he was involved with our 'Weber' department, and also designed the 'Timavo' range of manifolds. He was a lovely, gentle man whose company I always enjoyed and who I had a great respect for. Just before I left Radbourne he gave me the drawing for the inlet manifold required to fit a SU HS2 carb onto a 500. In those days the FZD was not available, so there were no manifolds for them, but as we now know, they were later fitted as a direct replacement for the SU on the Mini range. The FZD inlet manifold can be used (with no modification) for the fitment of the HS2 carb onto the 500/126 engine. Which of his books have you used for your reference?
thumb.gif
 
Hi Tom,

I've got the pair of books published in the early 80s. I believe that they are now available in a single volume.

I have read them many times over the years and for me they are the bible (old and new testament) for all things carburettor, but obviously Weber specifically. My only real gripe is that neither have an index.

Must have been lovely to actually know the guy - I've heard from other sources what a truly nice person he was. I reckon he'd feel right at home on this part of the bulletin board :)

Chris
 

Attachments

  • Passinni Books.jpg
    Passinni Books.jpg
    537.6 KB · Views: 48
Hi Tom. Not yet, but it's next on the list. For the moment I think we're going to work on making something that exactly suits our set up, but I'll let you know if we need the info. Thanks for the offer.
 
I notice there is a thick gasket between the FZD and the manifold. I'm assuming this is to insulate the carb from engine temperature?

Currently I'm thinking we will try without this, since it necessitates some longer bolts with nuts and drilling out the thread to hold the carb onto the manifold. The carb seems to be far enough away from the engine not to need much temperature insulation.

Any thoughts?
 
Ok, thanks Chris.

Went for a test run today. I'll try and post a video later in the week.

Is still dumping too much fuel, but we have compensated for it in how we've set it up.

Now need to give it a good run to make further adjustments. Not legal yet though.
 
Hi Tim;
I never fail to be fascinated in the different settings that people have on their carbs---and they all seem to work well! I DO have the thick spacer (about 1/4 inch) fitted between the carb and the manifold, with a gasket either side of the spacer. This DOES act as a heat barrier, and personally, I would retain it. You might be surprised as to how hot the inlet manifold gets, and by transference, the carb. If you remove the heat barrier you might suffer some hot start problems, especially if you don't have a fuel-return system on the carb (the constant flow of fuel in a 'fuel-return' system helps cool the fuel).
To affix my carb to the inlet manifold I made 2 long studs. Both thread into the manifold with the threads into the manifold made long enough that I could add a 'locking' nut behind the manifold flange. You might find that the top stud has to be 'waisted' just where it clears the carb flange in order to fit a smaller nut.
With my carb fitted as above, I don't have any 'hot-start' problems---I just crank the engine and 'catch-it' on the throttle--simples!
banghead.gif
thumb.gif
smile.gif
 
Tim;
Remember what I said re. the fact that the SU HS2 carb and the FZD having identical flanges? Have a look at the 'Burlen Fuels' site. Their (5mm) spacer (for the HS carb) is just over a £5 (and I expect that their postal charges are a bit more sensible) and is used as a heat insulator. With a gasket either side of the spacer, this will come up to 7mm. I would also recommend that you have a look at their adjustable throttle rods. They have left-and-right hand threads, so are very easy to adjust, and combined with the appropriate ball-joints, make for a very smart throttle link.
thumb.gif
smile.gif
 
Is it possible to alter the fuel feed in connector angle.....is it a threaded feed tube or is it fixed into the alloy casting?
Mine is in the horizontal and the fuel hose is being trapped by the engine cover and the hose is collapsing
I would ideally wont the connector facing downwards but im loathed to attempt to unscrew it for fear of snapping it off......?
Any idea where i would find an elbow version?
 
Last edited:
Ive attached the image showing fuel supply tube - do you know if you can unscrew it?
 
You must log in or register to reply here.

Similar threads

B
Tuning Dellorto FZD 32/26 Carb - Fresh Install Sound
Replies
3
Views
626
the hobbler
T
Hickory
Technical Signal Lamp Issues
Replies
3
Views
297
porta
porta
F
Technical USB Charging issues
Replies
3
Views
335
Noah500
N
T
Technical Starter motor issues - Fiat 500F 1970
2
Replies
39
Views
1K
ZaphodB
Z
P
  • Question
Tuning Starting issues
Replies
4
Views
496
Phild76
P
Back
Top