Technical Carburettor problems?

[rmribeiro]

Hi,

This summer I had a issue where one of the screws of the fuel enrichment ( Choke ? ) came of the and I did not notice it. I only noticed that all of the sudden the car would loose all power and then come back, and also some backfiring. I did about 30km like this because it was late nigh and need to get back home.

Next day I fixed it and the car idled ok, but the running it lacked power and sometime it had some backfiring and one time it simply stoped and would not start at all. So I decided to clean it put and purchased a repair kit. Assembled it all together, new gaskets new valve.

Today I assembled it. The car would barely start, very rough idle and if i tried to accelerate it would would not rev up and would stop running altogether.

Choke or no choke , it was very tough to start and then it would stop running after a minute or so.

Any help is appreciated. I am no expert mechanic but I really want to know enough about the fiat 500 to make sure I can keep it running while he keeps breaking

 

[rmribeiro]

Additional info:

When I put everything together i also put this gasket on the fuel enrichment ( choke ). Please see image attached.



It was not there before and I was not sure it was properly sealed. So I put this in. Not sure if it is needed but the fit was perfect.

Also, before the screw wen loose and opened the fuel enrichment ( choke ), I already had changed: Cables, rotor, rotor cap, and spark plugs. Because I was getting random backfires whiles going down. They did not help with the backfiring but at idle the car was running smoother.

The Carb is a 26IMB 10. The distributor seem to be from a 500R as te cap has a groove that 20 degrees to the closest pin ( on the bottom ). The car is a 500F from 1967.

 

[plasticpig1972]

Back firing when taking your foot of the accelerator is caused by air getting in.
Maybe Carb Flange not flat or Inlet Manifolds. You can correct this with abrasive paper on a flat surface. Or a hole in Exhaust System. Fuel level too high in Carb
so adjust Float to correct level. check what Carb you have for correct adjustment.
Alan

 

[Toshi 975]

You have not mentioned the dreaded condenser that is often the problem with misfiring

 

[rmribeiro]

"Back firing when taking your foot of the accelerator is caused by air getting in.
Maybe Carb Flange not flat or Inlet Manifolds."

I had that problem and when I rebuilt the carb I got everything as flat as I could.

My problem now is that after all this I cannot get it to start and run at idle much less accelerate.

I did not change the condenser. And I am worried to change it without some test I could do to pinpoint if it has a problem. Because If start changing everything I could be getting too many variables.


Timeline:
1- Car running great
2-Car started to have backfires going downhill
3- changed all the cables, rotor, ... > the car was running better but still with the backfires
4- Screw of the enrichment system came off -> leaving that part of the carb open and running it for 30km like that .
5- Fixed the screw - but after that lack of power in the car.
6 - Rebuilt the carb and put it back - no visible leaks os fuel and air

Now car does not start , idles very bad and then stops after sometime.

Does this help in the elimination process?

 

[plasticpig1972]

If you carefullyopen and look at the Points/Contact breaker do they look burnt.
Also is the Gap ok. If they are burnt change Condensor.
I've had flames come from the Exhaust on my Lotus Elan when the Condensor (made in China) was no good after 100kms.
If you change the Condensor do you have the old one which you could refit.
Alan

 

[rmribeiro]

I did not change the condenser. But I have a new one so I can check it.

What should be the correct gap in points ?

I suspect I have a 500R distributor because I had to buy a cap that is designed for the 500R.

 

[the hobbler]

Having looked through my 500 'Factory' w/shop manual, both my Haynes 126 w/shop manuals and the web-sites of the main Weber carb parts suppliers,I cannot find a gasket for the 'cold-start' device listed OR shown. I have also just striooed the 28IMB that I used on my engine until the FZD was fitted. It does not have gasket between the cover of the cold-start device and the body of the carb. Try running your carb WITHOUT the gasket---also make sure that the little finger that operats the cold-start piston is in the correct position when you put the cover back on.

 

[rmribeiro]

the little finger that operats the cold-start piston is in the correct position when you put the cover back on.

What is the correct position ? Because it has a spring it pulls the arm to one side ( not enriched ), inside the brass part is being pushed down by another spring. So i just slotted it in not sure where is pushing against.

 

[rmribeiro]

Hi,

Just checked the points- Not black

Then I checked the GAP on the points and could not see any gap. On the manual it says about .5mm so it should be pretty easy to see.

So I opened the screw and set it to .5mm. Started the car immediately !

And it had a high revs idle but stable.

Acceleration looked good ( without load).

So that is good news.

Let it charge up the battery in idle ( it was pretty drained with all the previous tries to start it ).

After some time tried to tune the idle with little success. Unscrewed the acceleration screw all the way - Still very high revs. Tried to fiddle with the mixture screw - no noticeable change.

I will be taking it to a proper mechanic to sort out the steering but still would like put my finger on what could be happening with the engine by myself.

 

[the hobbler]

The brass plunger in the cold-start device is 'waisted'---the operating finger goes in this 'waisted' section.The plunger should be free to move up and down when operated with a small screwdriver.
When you get the steering checked, if they adjust the toe-in (aka, 'tracking'), it is VERY important that you end up with the track-rods lengths identical. If this is not done, the 'Ackerman' effect is affected and you will probably end up with tyre squeal on corners. At the risk of 'teaching you to suck eggs', the Ackerman effect is the manner in which the inner wheel turns a slightly tighter radius on a bend than the outer wheel does.

 

[the hobbler]

To double check as to why you have a very high idle speed, disconnect the link between the carb and the 'yoke' on top of the fan housing--does this make a difference? If it does,make sure that the hand throttle is fully OFF, and check the accelerator cable is not sticking or the accelerator pedal is not sticking on its shaft.

 

[fiat500]

After some time tried to tune the idle with little success. Unscrewed the acceleration screw all the way - Still very high revs. Tried to fiddle with the mixture screw - no noticeable change.

I will be taking it to a proper mechanic to sort out the steering but still would like put my finger on what could be happening with the engine by myself.

You could try this:

https://www.fiatforum.com/500-classic/441969-introduction-my-new-1969-500l-14.html?p=4552207

or:

https://www.fiatforum.com/500-classic/441969-introduction-my-new-1969-500l-14.html?p=4552211

 

[rmribeiro]

I will get to the car on Monday and will try the suggestions.

Out of the bat I think the accelerator cable is moving ok and not accelerating. But I will check.

I will also put rubber ring in the idle jet. It was not there before but I saw some other post that had it.

 

[phoenix1]

Get rid of the points and condenser and fit electronic kit the you can eliminate the dizzy faults.

 

[rmribeiro]

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.

 

[rmribeiro]

Vídeo of it:

https://photos.app.goo.gl/gBCQCbBAHtYujCKg8

 

[rmribeiro]

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?

 

[F123C]

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.

 

[rmribeiro]

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.