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Old 02-09-2020   #31
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Re: Carburettor problems?

Quote Originally Posted by rmribeiro View Post
Put the carb back. Still had problems with accelerating.

Then I changed points and the condenser. And now it running good!

Not sure if it was the points or the condenser but there was a central pit in the points, I think those only happen when the condenser is failing!

I would like to rest the old condenser but do not know how.

I could not change the parts of the points, the new part was already broken on arrival, no contact part (Chinese part?).

The carb still has a leak issue on the top joint. I will post a slow motion video of the fuel escaping thru the joint.

Thank you all for all your help! I would never have thought it was a electrical issue.
It's not unusual for a 'pip' to form on one of the c/b points faces and a corresponding 'pit' to form in the other face - it's due to material transference caused by the small electrical sparking that occurs in normal use, even with a condenser that is functioning normally. In fact, in used to be normal practice to file down this little pip before resetting the points gap and then the ignition timing. In the good old days , garages used to sell 'points files' for this purpose - I haven't seen these for sale in many years, but I suppose you could use a flat 'needle' file or maybe a diamond-coated file, possibly even a diamond-coated nail file might work. The material for the points contact faces is usually tungsten, a very tough metal. Some people just swipe some abrasive paper between the contacts to clean them up - ideally you should use 'glass-paper' not silicone carbide paper, then just clean them afterwards with brake cleaner or similar. Make sure the contact faces are meeting squarely when closed for long service life. Apply a tiny amount of grease to the points operating cam to minimise wear on the points actuating heel.

There is no easy way of checking out a condenser at home (requires specialist equipment) so the usual advice is just fit a new one if in doubt.

Re:- the carb fuel leak - very weird, you seem to have cleaned and trued all the carb joint faces and fitted a new float valve, plus set the float height. The only thing I can think of that might cause the fuel leakage (I watched your videos) is if the fuel height is creeping up over the 45 secs and yet your engine doesn't sound like it's flooding.....

In one of your carb pics, I noticed a dent in the carb float - this would make me very suspicious. As Tom (the hobbler) has already recommended, best check out the float, not just for any fuel getting into it (shake it to test)which will cause flooding of the carb but also check it isn't binding anywhere in it's range of movement.

At least you're making progress

Al.
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Old 02-09-2020   #32
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Re: Carburettor problems?

It is not uncommon for the carb top cover to warp where people have applied too much pressure to the four mounting screws often when the gasket has started to disintegrate. I have straightedges out a few successfully.
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Old 02-09-2020   #33
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Re: Carburettor problems?

Quote Originally Posted by Toshi 975 View Post
It is not uncommon for the carb top cover to warp where people have applied too much pressure to the four mounting screws often when the gasket has started to disintegrate. I have straightedges out a few successfully.
Should I apply pressure using a vice with both top and bottom together? Or is there some other technic that is less risky?

I don't know if you noticed on the pictures but I added a nut to the second screw because I had no thread on top part. It has enough clearance so it is not hitting anything on the bottom part. But it could be blocking any flow inside the carb? Any recommendations ?
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Old 02-09-2020   #34
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Re: Carburettor problems?

Quote Originally Posted by rmribeiro View Post
Should I apply pressure using a vice with both top and bottom together? Or is there some other technic that is less risky?

I don't know if you noticed on the pictures but I added a nut to the second screw because I had no thread on top part. It has enough clearance so it is not hitting anything on the bottom part. But it could be blocking any flow inside the carb? Any recommendations ?
I am not sure what you mean by this nut and second screw thing. Looked at the pictures but not spotted anything.
So with the carb warped top I would remove the centre stud, assemble the top onto the carb body and press them together in a vice. Hold it up to the light and see if you can see light through the gap. If you do see light as the top may have a little spring in it put it back together again with 4 equal washers where the gasket would sit & held in by the screws. Re-apply pressure in the vice and keep testing the gap until it is even. It can be advantageous to reverse the bow just a tiny amount so that when you refit the top it pulls straight with a new gasket by the 4 screws.
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Old 02-09-2020   #35
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Re: Carburettor problems?

I added this nut that you can see a close up picture. It was not there but i needed to add it or else the screw would drop out.
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Old 02-09-2020   #36
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Re: Carburettor problems?

May I suggest that you remove the nut and use something like "JP Weld" to secure the stud in place.
I have just looked at my 28IMB and the top of my carb looks different to yours in that on the top of my carb the "Weber" is shown in the "EW" casting and the words "Carbureture WEBER made in Italy"---your carb top has a somewhat crude "W" and no "made in Italy".I would suggest that your carb is NOT a genuine Weber carb---this fact may be contributing to your problems.
I would suggest that you have a wander through E-bay and see if you can find a good 2nd hand GENUINE IMB carb. Some of the Italian e-bay sites are usually a good place to look---try "Lineaverde.rg@virgillo.it(also on:--- www.autoricambilineaverde.it)
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Old 03-09-2020   #37
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Re: Carburettor problems?

I tested the car yesterday.

- Started with almost no choke
- Very stable idle. No fluctuation
- Good acceleration

Quirks:
- Using choke at any moment ( cold or warm ) mad it almost die
- Turning the accelerator screw did not accelerate the idle
- Idle mixture had almost no effect on the idle. Had to fully close it to make the idle run rough.

Next steps:
- take the carb out
- Re adjust butterfly
- Take the screw ou and put JB weld in place
- Flatten the top of the Carb to eliminate the GAP or put a additional gasket
- Put the 112 injector back ( now it is 120 )
- Try to determine the origin of my Carb


Overall, great progress because of all your help!
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Old 03-09-2020   #38
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Re: Carburettor problems?

I hope you mean just a new gasket and not additional one , ie fitting two. I have got quite a few Spare Weber 26IMB carbs here plus bits if anything goes wrong.
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Old 03-09-2020   #39
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Re: Carburettor problems?

Quote Originally Posted by Toshi 975 View Post
I hope you mean just a new gasket and not additional one , ie fitting two. I have got quite a few Spare Weber 26IMB carbs here plus bits if anything goes wrong.
To be honest, if i cannot get it straight either by using a vice on sanding it down I really meant putting old gasket plus new one on top of each other...is this really a dumb strategy?
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Old 03-09-2020   #40
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Re: Carburettor problems?

Quote Originally Posted by rmribeiro View Post
To be honest, if i cannot get it straight either by using a vice on sanding it down I really meant putting old gasket plus new one on top of each other...is this really a dumb strategy?
Donít be so hard on yourself, I would say just misguided
Two gaskets is more likely to increase the bow in the top cover if the original is over compressed in the area of the screws. Just make sure that top cover is flat or a very slight bow in the opposite direction and all will be OK with one new gasket. Greatest respect to guys who are prepared to give things a go themselves
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Old 04-09-2020   #41
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Re: Carburettor problems?

Having looked again at your pic 10 of 12 and having consulted the official Fiat workshop manual (available free from the Downloads section of this website), some of what I said in my post #30 might not be exactly correct....

You asked if the pinhole in the carb bore should be covered by the throttle plate (or venturi flap as you refer to it)? I thought this was the idle mixture hole and therefore should be uncovered. However I'm now thinking that this is a Progression hole (or Transition hole as Fiat refer to it). Progression hole(s) should not be visible when the throttle plate is at the idle position (i.e. almost closed) - their function is to supply extra fuel as the throttle is initially opened. (so should only appear as the throttle is opened).

Your problems with idle, the mixture screw having little effect etc. remind me of what can happen when the throttle plate is not centralised >
throttle plate can't be fully closed - so too much air can pass,
progression hole is exposed - so extra fuel is being drawn in,
mixture screw has little effect - because it can't regulate the fuel from the progression hole,
engine bogs down on acceleration - mixture goes very weak because there is no extra fuel available from the progression hole (it's already being drawn in for idling).

Incidentally, having watched your video, I noticed you're a bit aggressive in operating the accelerator linkage. The 500 is an old design of car and carb and has a heavy crankshaft and flywheel (think inertia) - the carb doesn't have an accelerator pump jet/circuit, so for the engine to speed up from idle, it's relying on extra fuel being supplied from the carb progression hole, this'll take a little time, even the best tuned 500 engine of this type (no accelerator pump jet) will tend to falter a little if the throttle is opened suddenly, when testing the carb it's better/more instructive to slowly open the throttle.

Your plan to try to centralise the throttle plate sounds like a good next move
And, while you have the carb apart, double-check the float for fuel leaking into it (just shake it, any sloshing sound means fuel has gotten inside, this will cause the fuel level to rise in the float chamber) - I find it very suspicious that in your video showing your carb fuel leak, it takes 45 secs for it to occur and then it doesn't stop....

If you haven't already read it, there's a wealth of info in the Fiat workshop manual, including how the various sections of the carb operates, diagrams of the fuel circuits, plus all adjustments.

Al.
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Old 09-09-2020   #42
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Re: Carburettor problems?

I tested the float, putting it in hot water and verified that it is fully waterproof ( fuel proof :-p ). So the float now seems to be ok. Dented but floating with no leaks.

After some tries I finally got throttle plate to fit perfectly and cover the progression hole. I had to flip it remove all the screw, close it a few times and then fit the screws. I did not shift it when I cleaned it so the wrong positioning was done previously. But as F123C explained could justify

  1. throttle plate can't be fully closed - so too much air can pass,
  2. progression hole is exposed - so extra fuel is being drawn in,
  3. mixture screw has little effect - because it can't regulate the fuel from the progression hole,
  4. engine bogs down on acceleration - mixture goes very weak because there is no extra fuel available from the progression hole (it's already being drawn in for idling).


In terms of the top lid leak I have tried to get it flat on vice without success. Tried to sand it flat with very limited success. Not sure if I was able to get if flat enough and if cannot what options should I consider ?

In the fotos attached you can now see the progression closed when you have no acceleration.
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Old 09-09-2020   #43
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Re: Carburettor problems?

If you are happy with the rest of the carb I could probably sort out and send you a replacement top (or complete carb) it would be of the original type with the filter on the inlet with the big brass cover.
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Old 11-09-2020   #44
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Re: Carburettor problems?

I will try to test it early next week and see if it is OK. If its I will settle with not perfect but working

Thank you for all the help up until this point. Learned a lot!
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Old 16-09-2020   #45
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Re: Carburettor problems?

Update.

No leaks now!

Started with no choke
Stable idle at a good speed.
Tinkering with the idle mixture screw has an impact (previously it did not made any diference)

New thing I need to test:

- When warm If i pulled the choke, even if just a little bit the engine would die. Should it ? It did not do that before.
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