Register Login
Mr FIAT - Your #1 source for vintage car parts
Reply
 
Thread Tools Search this Thread
Old 28-08-2020   #16
Join Date: Aug 2020
Posts: 25
Thanks: 0
Trader Rating: 0
Portugal 
Re: Carburettor problems?

It's driving me crazy. The car just started with little choke. Then while warning up it started loosing power. Then pulled over. If i accelerated the car would not accelerate and would just stay in a rough idle.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

rmribeiro is offline Reply With Quote Quote 
Old 28-08-2020   #17
Join Date: Aug 2020
Posts: 25
Thanks: 0
Trader Rating: 0
Portugal 
Re: Carburettor problems?

__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

rmribeiro is offline Reply With Quote Quote 
Old 29-08-2020   #18
Join Date: Aug 2020
Posts: 25
Thanks: 0
Trader Rating: 0
Portugal 
I also checked the clearence of the valves and:

Valve 1: 0.15mm
Valve 2: 0.25mm
Valve 3: 0.25mm
Valve 4: 0.15mm

Does this look right?
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

rmribeiro is offline Reply With Quote Quote 
Old 31-08-2020   #19
Join Date: Jan 2014
Posts: 1,190
Thanks: 181
Trader Rating: 0
Ireland 
Re: Carburettor problems?

Afaik, the valve clearances should be 0.15mm (0.006 in.) cold, on all valves.

But I don't think larger than correct valve clearances on your inlet valves is causing your problem. (you can hear the valve clatter in your video).

When you opened up the points gap, did you turn the engine to where the points were fully open first? Also did you reset the ignition timing afterwards?
(opening up the points gap will advance the ignition timing). A very large points gap will reduce the spark strength. Very advanced ignition will raise the idle speed, make it very uneven and because the spark is occurring way too early can prevent the engine from speeding up as the accelerator is pressed.

Listening to your engine in the video, the problem sounds more like an ignition problem, are you sure there isn't a loose/poor connection somewhere? It's almost like the ignition system is momentarily cutting out when the engine rocks around so badly. As you've renewed the HT leads, maybe check the LT lead between the coil and distributor, especially at both ends and check it's not shorting to earth anywhere along it's length.

An air leak can cause rough running, high idle speed and prevent the engine from speeding up when the accelerator is pressed. So can a low fuel level in the float chamber - did you check/adjust the float level after fitting the new valve. It seems your problem got worse after you rebuilt the carb. Is the carb. spotlessly clean inside? E.g. a blocked main jet will prevent fuel reaching the emulsion tube and consequently the progress holes in the bore of the carb - when you try to accelerate the engine, the extra fuel has to come through these progression holes, otherwise the engine won't speed up - in fact the extra air being admitted by opening the throttle weakens the idle mixture causing the engine to almost cut out - just as your engine seems to be doing. (your engine also then seems to run better when you close the throttle).

It might be time to go back over everything you've done and double-check that you haven't accidentally added in another problem. If any replacement parts are different from the originals e.g. rotor arm, distributor cap, etc. maybe try refitting the originals and see if there is any improvement.

Al.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides


Last edited by F123C; 31-08-2020 at 03:18.
F123C is offline Reply With Quote Quote 
Old 31-08-2020   #20
Join Date: Aug 2020
Posts: 25
Thanks: 0
Trader Rating: 0
Portugal 
Re: Carburettor problems?

Thank you for your reply F123C!

Answering your questions:

1- When you opened up the points gap, did you turn the engine to where the points were fully open first?

I tried to rotate the engine to the position where the topmost part of the lobe was longer. I measured the GAP at the topmost part of the lobe. There are 2 per 360 degree rotation. I think they are equally spaced.

2- Also did you reset the ignition timing afterwards?

I do not have a timing light ( gun ) so i was afraid I would make everything worse so did not touch that part. But if it was such a problem It would be bad at idle or cold acceleration no ?

3 - sounds more like an ignition problem, are you sure there isn't a loose/poor connection somewhere?

I replaced the wiring, rotor arm and cap and spark plugs. Everything seems to be tight and in place. I did not replace points nor capacitor ( but have a spare of both), so not had more variables. I visually checked if I saw any possibility of shorting and did not find it. Everything has a lot of clearance to the next component.

4 - did you check/adjust the float level after fitting the new valve.
Yes.
Opened it again measured 9MM to 15M so it was not perfect. Bu it hard to get a good measurement.


5 - It seems your problem got worse after you rebuilt the carb.

It is not worse, it is more a less the same . A little be better at starting.

6 - Is the carb. spotlessly clean inside? E.g. a blocked main jet will prevent fuel reaching the emulsion tube and consequently the progress holes in the bore of the carb?

Opening it again and cleaning it with a engine/brake cleaner stuff. I will post pictures of it in a exploded view

I think it might be useful for others because i Have seen 28 IMB carb pictures but not 26 IMB 10. There are a few diferences.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

rmribeiro is offline Reply With Quote Quote 
Old 01-09-2020   #21
Join Date: Jul 2012
Posts: 2,635
Thanks: 202
Trader Rating: 0
United Kingdom 
Re: Carburettor problems?

The easiest way to measure the float level is to use a drill (or a tube or rod) of the correct dimension, which is 7mm when the carb top is held in a VERTICAL position--don't worry too much about the '15mm' dimension. Did you give the float a shake and check that there is no fuel inside it? If there is, that will affect the running ofthe engine--it needs to be replaced (cannot be repaired).
Look on your dynamo-belt pulley--there might be a small 'flat' on the outer side of the casting, which will line up with the timing mark on the oil-filter cover (which will only fit onto the pulley on one position). There will be a corresponding mark (small raised cast 'line') on the timing-chain cover. If you have 'points' ignition you can statically check the timing with a small timing light (bulb with 2 wires and small 'croc-clips' will suffice).The correct static timing for the 500 engine is 10 degress before top dead centre (BTDC), or the mark on the pulley/filter when it is 13mm before the mark on the timing-chain cover (the engine turns clock-wise, looking from the rear of the car). Clip one of the wires from the bulb to the distributor side of the coil and the other wire to the body (earth). Ensure rotor arm is aligned with no '1' on the distributor cap. Remove ignition lead from coil or distributor cap (safety item--so that the car doesn't start on you). Turn engine to set timing marks on pulley/t-c cover, turn ignition on. Turn distributor CLOCKWISE until light is out---then turn distributor ANTI-CLOCKWISE until light just comes on.tighten distributor clamp nut, refit ignition lead.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

the hobbler is offline Reply With Quote Quote 
Old 01-09-2020   #22
Join Date: Jan 2014
Posts: 1,190
Thanks: 181
Trader Rating: 0
Ireland 
Re: Carburettor problems?

1) Re-check the contact breaker points. If they are used, a pip can form on one face resulting in the gap not being set correctly.
Slide a piece of clean white paper/card between the points contact faces to check for any contamination (any oil on the feeler gauges gets transferred when adjusting the gap). Clean the contact faces with Brake cleaner spray or similar.
____________________________

Checking the ignition timing without a timing light/gun.:-

Remove the distributor cap, rotate the engine, with the ignition turned on, to where the timing mark on the crank pulley is approx. 30mm to the left (anti-clockwise) of the fixed timing mark on the timing cover.
Connect a test light between the wire going to the contact breaker points and a good earth point. (With the points closed, the light will be off, when the points open, the light will go on).
Now turn the crank and see when the light comes on, this is your static ignition timing setting. The light should come on (i.e. the points should just open) when the crank timing mark is approx. 13mm to the left of the fixed timing mark. If this is not correct, loosen and turn the distributor until it is o.k.
Timing the ignition statically is quite sufficient for normal use.

Alternatively, the timing marks can be set 13mm apart, then loosen and rotate the distributor until the light comes on (i.e the points have just opened), then nip up the distributor clamp.

If you don't have a test light, you can either watch for the small spark that occurs between the contact faces of the points as they open, or watch carefully to see when the points just start to open. (some people place a sheet of paper between the contact breaker points, when you can easily pull it out, the points have just separated).

When you think you have it adjusted correctly, rotate the engine forward one full turn to double-check your adjustment - don't turn the engine backwards if you miss the point where the points open, there'll be some backlash in the distributor drive which can give an inaccurate reading.

____________________________

You changed the distributor cap and rotor arm? - are they exactly the same as what were originally fitted?, if not, try refitting the originals in case there is a difference.
_______________________________

Whenever you're faced with a problem that could be either ignition or carb., it's usually best/easier to rule out any problem with the ignition system first, then tackle the carb.
_____________________________

Re:- your carb.
In the Downloads section (blue band at the top of this page) there is a section on the 500 (Classic) - if you select this, you can download (for free) a copy of the factory Fiat workshop manual.
In this, the Weber 26.IMB is covered, along with the other carb models.
For your carb, float adjustment is covered on p.39 (they show 7 and 15mm, - your 9mm will result in the carb fuel level being too low), choke unit is on p.41 and the carb differences on p.40.
__________________________

Some other things to consider are :-

Failing condenser, as several others have already mentioned (condensers seem to give a lot of trouble on the 500, especially modern aftermarket ones). If in doubt, fit a new one. (you mentioned you have one but not fitted yet?).

Fuel blockage? Did you clean the fuel mesh-type filter in the carb? It's under the large brass nut (iirc 19mm?) in the carb top cover adjacent to the fuel inlet pipe.

Failing fuel pump? To check output, disconnect the fuel pipe from the carb, place open end in as container (glass jar) and spin the engine over with the ignition off, to see if you have adequate output from the pump.
___________________________

In summary:-

Check points gap and clean.
Check/adjust ignition timing.
Fix choke as per the workshop manual.
Set float upper/lower levels as per the w/shop manual.
Check fuel flow rate and that filters are clear. There are 3, mesh screens in fuel tank pick-up pipe, fuel pump (under the top cover) and at the carb fuel inlet.
Fit new condenser (1st or last, your choice).

Al.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

F123C is offline Reply With Quote Quote 
Old 01-09-2020   #23
Join Date: Aug 2020
Posts: 25
Thanks: 0
Trader Rating: 0
Portugal 
Re: Carburettor problems?

Several pictures of the carb, while assembling it back together.

There is no mesh fuel filter on mine. No place to put it

also the cap on the spring of the "choke" is different from most pictures I have seen.

The Venturi tube seem to be made of plastic ( is this possible ? )

I posted a picture with all the number of the metered holes. Might be useful for some one else.

When close the venturi flap partially closes the pinhole at the bottom. Should it partially close or should it be clear from obstruction?
Attached Thumbnails
Click image for larger version

Name:	IMG_20200831_203535.jpg
Views:	9
Size:	870.9 KB
ID:	212234   Click image for larger version

Name:	IMG_20200831_204117.jpg
Views:	5
Size:	850.2 KB
ID:	212235  

Click image for larger version

Name:	IMG_20200831_194033.jpg
Views:	11
Size:	612.4 KB
ID:	212236   Click image for larger version

Name:	IMG_20200831_194056.jpg
Views:	15
Size:	630.0 KB
ID:	212237  

Click image for larger version

Name:	IMG_20200831_195828.jpg
Views:	7
Size:	907.1 KB
ID:	212238   Click image for larger version

Name:	IMG_20200831_194112.jpg
Views:	7
Size:	972.7 KB
ID:	212239  

Click image for larger version

Name:	IMG_20200831_195636.jpg
Views:	7
Size:	706.9 KB
ID:	212240   Click image for larger version

Name:	IMG_20200831_204521.jpg
Views:	17
Size:	871.3 KB
ID:	212241  

Click image for larger version

Name:	IMG_20200831_193753.jpg
Views:	7
Size:	970.7 KB
ID:	212242   Click image for larger version

Name:	IMG_20200831_195644.jpg
Views:	11
Size:	637.8 KB
ID:	212243  

Click image for larger version

Name:	IMG_20200831_194038.jpg
Views:	8
Size:	577.0 KB
ID:	212244   Click image for larger version

Name:	IMG_20200831_204533.jpg
Views:	10
Size:	731.8 KB
ID:	212245  

__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

rmribeiro is offline Reply With Quote Quote 
Old 01-09-2020   #24
Join Date: Jun 2009
Posts: 1,106
Thanks: 89
Trader Rating: 0
United Kingdom 
Re: Carburettor problems?

Never heard of or seen a plastic Venturi. The lack of a fuel filter on the inlet means that is from one of the cheap repro carbs but the body does look More original. Could it be made up from bits & bobs. The brass slider on the choke should be easy to remove and clean and with the emulsion tube I find that a small screwdriver will fit nicely down the middle and with a bit of a wiggle the bit will ease out allowing you to clean down there. Other parts look pretty standard.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

Toshi 975 is offline Reply With Quote Quote 
Old 01-09-2020   #25
Join Date: Aug 2020
Posts: 25
Thanks: 0
Trader Rating: 0
Portugal 
Re: Carburettor problems?

@toshi - I am not sure it is plastic. But it is very light. It could be tin but it does not fill cold like all metal parts. The Carb does not feel like it is new, it has all sorts of dents and scratchs all over.

I just assembled everything back together. I did not know I could remove the emulsion tube out. So I did not force it out.

I did level the bottom now. It was warped before.

@F123C

Latter this week i will do

1 - Put the carb back in the engine
1.1 - Fix choke as per the workshop manual. : done
1.2 - Set float upper/lower levels as per the w/shop manual. Done

2- Check points gap and clean.


3 - Check fuel flow rate and that filters are clear. There are 3, mesh screens in fuel tank pick-up pipe, fuel pump (under the top cover) and at the carb fuel inlet.

I only have one at the exit of the fuel tank. It is new and is clear.

4 - Fit new condenser (1st or last, your choice).

5 - Check/adjust ignition timing.

Still a little be scared of messing with this . Will read everything you posted and try to find video or something to make sure I do not mess the car
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

rmribeiro is offline Reply With Quote Quote 
Old 01-09-2020   #26
Join Date: Jun 2009
Posts: 1,106
Thanks: 89
Trader Rating: 0
United Kingdom 
Re: Carburettor problems?

As far as I am aware there were some carbs made under licence in Spain and were of a reasonable standard then there were some pretty nasty ones made in China. I had to check so looked at my spares in my garage. On the Italian carbs they have Bologna on the top cover and Italy on the main body to the left of the choke mechanism.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

Toshi 975 is offline Reply With Quote Quote 
Old 01-09-2020   #27
Join Date: Aug 2020
Posts: 25
Thanks: 0
Trader Rating: 0
Portugal 
Re: Carburettor problems?

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.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

rmribeiro is offline Reply With Quote Quote 
Old 01-09-2020   #28
Join Date: Aug 2020
Posts: 25
Thanks: 0
Trader Rating: 0
Portugal 
Re: Carburettor problems?

https://photos.app.goo.gl/Cgaq4pUc9H3RxSQ87

Video of it accelerating, while warm , and video of the carb in slow motion with some drops of fuel escaping ( 45 seconds onward )
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides


Last edited by rmribeiro; 01-09-2020 at 22:44.
rmribeiro is offline Reply With Quote Quote 
Old 02-09-2020   #29
Join Date: Jan 2014
Posts: 1,190
Thanks: 181
Trader Rating: 0
Ireland 
Re: Carburettor problems?

Apology to 'the hobbler'

Sorry Tom,

I was busy typing my post #22 (overlong as is my norm!) which included looking up some info in the Fiat workshop manual for the OP and missed your post #21 describing the procedure for adjusting the ignition timing statically - I didn't mean to duplicate what you had already written.

Regards,

Al.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

F123C is offline Reply With Quote Quote 
Old 02-09-2020   #30
Join Date: Jan 2014
Posts: 1,190
Thanks: 181
Trader Rating: 0
Ireland 
Re: Carburettor problems?

Quote Originally Posted by rmribeiro View Post
Several pictures of the carb, while assembling it back together.
-----------------------------------
-----------------------------
----------------------

When close the venturi flap partially closes the pinhole at the bottom. Should it partially close or should it be clear from obstruction?
Great job with the pics, very clear.

The venturi flap is usually referred to a 'butterfly valve' or 'throttle plate' in workshop manuals written in English, might help avoid any confusion.

I wasn't aware that you had dismantled the carb this much.... my experience is that people can get themselves into great difficulty when they remove this throttle plate. And into even more difficulty if they bore out worn spindle holes in the carb body to fit bushes but bore the holes off-centre....

Anyway, looking at pic 10 of 12 you've posted, it seems to me that the throttle plate maybe isn't centralised? - with the idle speed screw on the throttle linkage backed off fully, the throttle plate should close off the carb. bore completely. As things stand, there seems to be a slight gap on the right side but the throttle plate is touching the carb bore on the left side. The pinhole that you mention is the where the fuel at idle comes into the carb - it doesn't have to be completely uncovered but it does have to be positioned so that the small amount of air that passes around the throttle plate at idle (i.e. when you turn in the idle speed adjusting screw, it opens the throttle plate very slightly) can cause a depression (vacuum) across the hole, thus drawing the fuel out.

That throttle plate (butterfly valve) can be fitted in 2 ways, one right, one wrong! There's a slight chamfer along 2 areas of the circumference to allow the plate to exactly match the carb bore when closed, it's important it's fitted correct way around and then centralised. To centralise it, back off the idle speed adjustment screw fully, loosen the 2 screws holding the throttle plate, snap the throttle closed a couple of times to centralise the plate (hold the carb up to the light to ensure it's centralised i.e. that no light can be seen around the plate's circumference) then hold the throttle closed and tighten the 2 screws. These screws should have been coated when fitting with a fuel resistant thread locking compound and are usually 'peened over' to ensure they can't ever fall out.

(Iirc, the figure 78* on your throttle plate indicated the amount of chamfer on it's edges? or maybe it's the angle of the throttle plate when fully closed?)

In pic 8 of 12, the idle jet holder can be seen - it's the large brass slot-head screw with the rubber O ring that's partially unscrewed. Some of your other pics show this removed and alongside other carb jets etc. You don't appear to have separated the idle jet from this idle jet holder - the idle jet part (it has 45 on it) just pulls out of the idle jet holder (you might have to carefully use 2 pairs of pliers). It's important that the recess inside the idle jet holder is cleaned along with the idle jet. The idle jet has a large cross drilling and a tiny hole in it's end - this is the metered part i.e. 0.45mm. Cleaning of this jet can be done with the carb on the engine, even at the side of the road - unscrew, separate into it's 2 parts, blow through the idle jet part, hold it up to the light to check that the tiny hole is clear, then reassemble and refit to the carb.

Al.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

F123C is offline Reply With Quote Quote 
Reply
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump
Similar Threads
Thread Thread Starter Forum Replies Last Post
(T) Fiat 900t carburettor problems... BristolKarl 850T / 900 5 02-01-2018 21:49
(T) carburettor El cargador 500 (Classic) 9 05-05-2016 22:27
(T) Carburettor help please nerodino 500 (Classic) 6 07-08-2010 15:48
(G) Carburettor Robot Ducato 0 25-07-2007 09:13
(T) 1.6 Carburettor Trancendental Tipo (Classic) 0 10-01-2006 03:09