Tuning Backfiring at idle 1970 500F

[CsFiat]

Well, sorry for the delay. New coil installed and I am slightly discouraged as there is still not much change in the situation. The car runs better since the install of the 'pipette' in the bakelite drip tray but it's still rough and on a test run it cutout a couple of times. Top end is still sluggish also. Not sure what to try next. I think I will basically start from the start again and see if that gets me anywhere.

 

[CsFiat]

Can the voltage regulator cause a drop out in the coil. The 'cutout' I mentioned seems like for 1/2 a second the power was turned off. So it does kind of a lurch then continues on like nothing happened. Re-timed and the idle/run seems better.

 

[Vitesse]

Hi Michael the voltage regulator is all to do with charging the battery. The car uses a dynamo as opposed to an alternator. A dynamo will not produce much voltage at idle so the voltage regulator cuts out the dynamo at low speed when the dynamo output voltage drops below the battery voltage. This stops the dynamo drawing current from the battery, once it reaches a higher speed and the dynamo is producing a higher voltage level than the battery the dynamo is cut back into to allow it to charge the battery. It also has a regulating switch which prevents the voltage from the dynamo getting too high and effectively frying the battery.

So the answer to your question is no because the battery is providing the low voltage to the coil and is a different circuit from the charging circuit.

It's difficult to say where to go next, if you are sure the timing etc is ok then it could be possible that your cutout could be caused by fuel starvation?

Tony

 

[CsFiat]

I kinda thought that but wanted to make sure. I am pretty sure the timing is okay (getting that part pretty down pat now ) I do note bubbles in the fuel filter but someone said that was not unusual. The 'mechanic' that did the original work said he "Renewed fuel pump due to leaking and pumping out oil." and considering the fine job he did in other areas there might be a problem in that area too. Is the fuel pumps something one can take apart and check or am I looking at a replacement? Thanks

Michael

 

[Vitesse]

The one on my car you can take apart but I have a spare that is a sealed unit. If you have a ring of screws around the top then you can. I must admit I never have taken one apart but the manual actually recommends a periodic inspection to check for sludge and crud that may have built up inside. I guess it makes sense as you can get sludge etc. in the bottom of the tank that builds up over the years.

Here is what the manual says, I hope it is clear enough to read.

 

[Paolo66]

I've taken mine apart before and it is really easy. Be careful and go for it. There's also a measurement for how much the pump rod should stick out from the spacer. Off the top of my head I think its 2mm but check in the manual first

 

[CsFiat]

I have a manual that I got offline. The one you have there Tony does not strike me as the same one that is on ours. . . . I think the fuel pump is the next place for me to work on. I am guessing that if there is enough bubbles coming up from the pump then you might get a 'bubble' that would interfere with the proper operation of the motor. I will see if I can squeeze it in the weekend somewhere. The seal if I remember correctly looks like some kind of liquid gasket. Have to take a closer look before I start. Thanks again for the help guys!

 

[Vitesse]

Hi Michael that is from the official Fiat workshop manual produced in Milan for English dealerships, I refer to it as the 500 bible. It goes into every tiny detail of the 500. I think they are quite rare but it is about an inch thick.

Air bubbles in the filter between the fuel pump and carb are quite normal at tick over. I would imagine that once the engine is being driven at speed these will obviously go but I don't imagine anybody has actually managed to get themselves in a position to witness this. Well I hope not.

 

[gordinir8]

Hi Michael that is from the official Fiat workshop manual produced in Milan for English dealerships, I refer to it as the 500 bible.

This is an older post but is this workshop manual you are refairing available to buy? Maybe a good copy?

 

[Paolo66]

This is an older post but is this workshop manual you are refairing available to buy? Maybe a good copy?

If it's the same one as mine and I think it is, I got a reprinted copy off Ebay. It has an orange cover and as Tony says is about an inch thick. It goes into most things in a bit more detail and covers models from D up to L. Worth the money in my view.

 

[Paolo66]

You can find it here Thomas.

http://www.ebay.co.uk/itm/Fiat-500-...945243?hash=item3ae3435a5b:g:X6IAAOSwkShY~x6l

 

[gordinir8]

Thank you if you say it worth then it is, I will go for it.
There are things that missing from Haynes manual and I hope they are there.

 

[the hobbler]

Yes, that workshop manual is well worth it! The projection of the fuel-pump operating rod is 1-1.5mm on the outside of both gaskets and the spacer, JUST AS THE ROD STARTS TO BE MOVED OUT by the lobe on the cam-shaft.

 

[Paolo66]

Yes, that workshop manual is well worth it! The projection of the fuel-pump operating rod is 1-1.5mm on the outside of both gaskets and the spacer, JUST AS THE ROD STARTS TO BE MOVED OUT by the lobe on the cam-shaft.

Be aware Thomas that measurement is for a 500 engine and pump. If you have a 650 engine the measurement is 1.5-2.0 mm. I've just been through all this when putting my engine back together and found I had been running with a 500 pump on a 650 engine. The 500 pump only has only got just over 1mm movement in the mechanism and I had 2 mm movement on the rod. All sorted now with a 650 pump and correct spacing.

 

[fiat500]

I've never measured that dimension and so must have been lucky to escape the problem.
From experience in the future I would have to measure carefully because I would fit the thicker 650 spacer on a 500 engine. Incidentally, I would try to do the same at the carb because fuel evaporation after leaving the engine a few minutes when hot appears to be much reduced on the later engine.

 

[g8rpi]

I wonder what happened to the original thread. @CsFiat are you still on here? did you get the car sorted?


Robert G8RPI.

 

[the hobbler]

With respect gentlemen, being that Gordinir8 has a 650 engine in his car, the information I supplied was out of the Haynes manual for the '652cc 126' manual, and NOT the 500/500D manual (which strangely, does not give that measurement in either the 'engine trouble shooting' section or the fuel-pump section) which is manual that I have--a proper 'Fiat publication' edition.

 

[Vitesse]

This is the original one dated 1963. I bought it off eBay years ago, it's got that old book smell! Mine is a ex library book so it's in quite good condition covered in cellophane.

 

[the hobbler]

That is exactly the same as my copy, except mine is quite as smart! It was gifted to me by a friend who was helping sort out an old Fiat dealership that was shutting down. My (mechanical) parts manual came from the same source and is of the same age.

 

[Nick Striker]

I’m curious about that hole too. Just rebuilt my carb 28 ran it stopped and fuel and vapors were coming out. Very scary. What do you think I did wrong.