So what is the truth? The Italians told me I needed an additive in my tank to run on unleaded fuel, the English told me I didn't.

So if I haven't used an additive and I should have done, how many miles before I would expect to see a problem?

What would be the symptoms?

What damage would have occurred and what would be the solution?

Thanks for your help!

Regards, Ian

^
If the engine hasn't been prepared for unleaded you do need an additive.

Failure to use it will cause burned out valves and stems.

-Tazio

The lead (tetra-ethyl lead, not the same stuff as on the church roof) in fuel was added initially as an octane booster. It was then found that it also lubricated the valve seats allowing cheaper softer materials to be used for the valve seats.

With unleaded fuel, harder valve seats had to be fitted. So as Tazio says, if its not got them trouble will come.

Without the lead or hardened valve seats, the valve seats will gently wear, receding into the head allowing the valve to burn. Damage will also occur to the stem and possibly the guide as combustion gases escape early.

How long will this take? That's an impossible question. It will depend on how much lead had coated the seats before unleaded fuel was used. Some people have used engines for years without trouble. How it is used and for how much will also affect time. First symptoms would be valve clearances closing up. Mostly when we check these we expect them to have opened, so this is a good early warning.

If the engine is running fine, valve clearances are ok and a compression test shows ok, all is currently well. Additives are available, so these can be used. Search elsewhere on these forums to find recommendations.

If problems are discovered, its head off time for new seats and valves, possibly also guides.

I'm definitely with the English on this one- I think valve seat additives are largely unnecessary in a Fiat 500 engine.
My experience with unleaded fuel dates back to my early days of Fiat 500 ownership in New Zealand when leaded fuel was discontinued altogether in the early 1990's.
At the time I was employed as a mechanic at an independent workshop where we specialised in Italian cars but worked on a comprehensive range of vehicles including dyno tuning of everything from 1920's Alfa Romeo racecars through to modern turbocharged vehicles.
Certainly cast iron headed vehicles such as Minis and Fords often suffered from severe valve seat recession, closed clearances and burning especially when run at prolonged high RPM on unleaded fuels.
Interestingly we found that all the alloy headed Fiat engines were remarkably tolerant of unleaded fuels and experienced no significant decrease in valve sealing or compression over long periods.
At that time I drove a 1972 Fiat 500F as a daily driver which had an original 500 head and valves with 650CC barrels and pistons. Our experience suggested that no additive was necessary but I decided to carefully monitor valve clearances and compressions to verify this.
Over a period of several years I regularly checked compression and valve clearances and despite significant heavy use of the vehicle with prolonged high speed running no ill effects were observed.
In fact I still own this vehicle and the engine is still running fine with excellent compression 22 years later having travelled around 30,000mls on unleaded fuel with no adverse effects.
My view is that if the engine is in good running order and properly maintained it should be able to handle unleaded fuels without any additives required.

I too thought that with an alloy head, the car would have had hard enough valve seats to cope. The car has now done 2,500km in my hands, 2,000 of which was coming back from Italy - all with an additive. So I have done only a few hunded km with no additive since we got here.

There was a reason for my question, of course!

After three days to do those 2,000km with no problems, all the issues have started since we got home! First it wouldn't idle, so I stripped the carb and freed up a partially seized throttle spindle.

Then it came home on flatbed after refusing to start, having driven perfectly to the destination. I think the dizzy had moved.

Then it started spluttering and I thought a good run would sort that as all it had done in recent weeks was short starts and stops. One minute it runs sweetly, then misfires, then stops firing, then picks up and back to normal, then repeats the process. Its like driving a baby kangaroo! Anyway, it came back on the end of a rope last time as it wouldn't make it up the hill home! It seems to be getting worse.

I decided it might be fuel, so stripped the fuel pump. Couldn't get the right overhaul kit, so we now have a new pump and inline filter. I took the pickup out of the tank to make sure that was OK and blew down the fuel line (quite hard work!!). I am now at a loss. I have perfect ignition, points gap, timimg, plugs, leads etc I am sure.

I have clean fuel arriving at the carb, I have checked the float movement, cleaned the main jet again and again, but the problem remains.

When it runs perfectly, it sounds really sweet, crisp exhaust note etc - spot on. Do I buy a new carb? It's not the original carb as it is an IMB 10, whereas it should be a 2 or something, but a new one is really expensive and no guarantee of a fix.

I am completely stumped!! I thought these cars were so simple and reliable - right now we have lost faith and we daren't go anywhere!

Help!

Ian

My first guess would be ignition condenser or points for those issues. Kangarooing is more likely ignition although everyone aims at the carb first.

Rather than we all guess, do some basic diagnosis.

1. Check condition of ignition points. If in good condition ensure gap set correctly and distributor shaft does not have excessive play.
2. Any signs of burning of points, replace the condenser. Might be a good idea to replace anyway. Get a good one, not a cheap one.
3. Set the ignition timing.
4. Check the valve clearances.
5. Do a compression test.
6. Check condition of spark plugs. Colour of tip and condition may help diagnosis.

And use high octane, quality fuell...!!
This particularly car has probably run on (Italian) 98 octane fuel with an additive.
I suggest to use Millers VSP+ additive, together with low or no ethanol BP Ultimate or Shell V-Power.

Interesting stuff.

We have always used an additive in ours which has a 650cc 126 engine.

My philosophy is that it can't do any harm to use an additive....... can it??

1) Points are new, gap is spot on (well, within one thou!)
2) Condenser is new too.
3) Ignition timing is perfect (well, within 1 degree!)
4) Valve clearances were reset within the last 100 miles
5) Not done a compression test.
6) Plugs are new and perfectly gapped, looked lightly black, but then the car was on choke.

It is the intermittent nature of the problem that is confusing me. Sometimes it ticks over or runs perfectly. Wouldn't a compression problem give me a permanent problem?

Ian

Suffered the exact same problem on my 500 back in the late 70s before the advent of unleaded. Turned out to be a broken LT lead between the coil & dizzy.

The wire had broken within the insulation leaving no outward sign of failure - put that down to work hardening from vibration over time.

I've being running my fiat 500L for over the last 10 years, it has now over 80k miles, all on unleaded fuel, no additives, and driven at top speeds must of the time. I do a lot of long straight road driving, avg 4k revs at 90 kph.

I've come across the hopping problem in 3 different cars, 1 of them mine. 2 were down to the wire from the coil to distributor, it will look okay but inside breaking up, it should be repleced during a service/points change to be safe.

The 3rd was down to the wire damaged going into the condensor, i guess i did this while moving the distributor while setting the timing and trying not to get burned. It was a new condensor fitted, discovered the wire after stripping carb, changing plugs, redoing points, checking valve clearence.

I suspect you gentlemen are geniuses!

I will replace that wire asap and double check the condenser. That diagnosis explains the first breakdown - actually diagnosed as the coil! When I went to fix it, I got a nice belt off the old coil, so never found out what was wrong, I just reckoned that in checking the connections I had accidentally repaired whatever was wrong!

It would certainly explain the current issue and why everything fuel related is doing nothing to help.

It also puts my mind at rest that we have bought a good little car!

Fingers crossed, but I bet you are right!

I will let you know!

Your honour and your dragonship, I thank you!

Ian

First, congrats on a 2000km troublefree trip. Your butt must still be buzzing.

Second, I agree with the diagnosis of a bad wire--or ground, or other electrical contact problem. Check everything while jiggling.

Third, there was a lot of discussion on unleaded fuel in the UK 500 group list and I got the impression that the 500 was fairly impervious to damage that way. Of course, all those with heroic stories of many miles on unleaded might be running cars in which valves or seats had been replaced in the past with ones designed for unleaded; after all, replacing valves in a forty or fifty year old car would not be unheard of.

I am giving my 500L (slowly, as funds allow, being converted into a replica Abarth 695) a paint-work 'refresh' this winter. Whilst it is at my friend's bodyshop, I will have the engine out, fit a 'warmer' cam and fit a slightly modified head. I have had larger (36mm) inlet valves fitted and harder valve seats all round. I decided to go this way as it was going to have new inlet seats, so it might as well have hardened exhaust valve seats at the same time. I have heard a variety of stories as the requirement of 500s for hardened valve seats, but decided not to risk it. Continual use of 'leaded' additives will work out quite expensive over a fair bit of mileage, so the harder seats may well prove to be the more economical proposition. My reccomendation is; if the opportunity arrises, fit the harder valve seats.

Well, maybe you aren't the geniuses I was hoping you were!! I have replaced the coil to dizzy wire - no change. I have replaced the coil - no change.

I was going to change the HT lead, but the one I received is only a few inches long as if the coil is supposed to be the same side as the dizzy, which it isn't - it is on the neaside inner wing - miles away!

I will order a new set of leads and see what happens - if it isn't the HT - what next? The coil to the front of the car - where exactly does that wire go? Through the bulkhead towards the back seat and then?

Will keep you posted!

Ian

The coil on my car is mounted on the inner wing on the same side as the distributor. I think that's where it is meant to be. Also, check all ground connections, whether wired or something like a screw to the chassis.

Hi Ian,
Your Coil is in the correct position for your year- later models had it mounted on the other side near the distributor which means a much shorter coil and low tension lead.

You can move the coil over to the distributor side simply by extending the positive lead around the back of the engine bay and then you can use a much shorter coil lead and low tension lead to the distributor.

One thing that you may want to check is that you have a correct 12V coil- I have found several 500s over the years that have a 6V coil fitted without a ballast which leads to all sorts of intermittent ignition problems.

I had one case recently where the owner told me that he had replaced all the ignition components including the coil and had the same problem- turned out he had replaced one incorrect (6v) coil with another identical new incorrect one and the problem persisted...

Check and ensure that the coil has 12V stamped into it somewhere- if in doubt use a ballast resistor in line with the positive wire and retest.

Regards, Damon

This is definitely an ignition issue.

Follow the low tension all the way from the ignition switch to the coil, to the points and from the distr. baseplate to its body. That last one can be troublesome on any car due to constant flexing as the baseplate rotates. They can break inside the insulation. Needs to be replaced with the right cable. Ordinary insulated cable is not flexible enough.

Check that nothing fouls or earths out as the distributor baseplate moves.

A worn/faulty ignition switch can cause this, so don't assume it will be in the engine bay.

Check engine earth cable.
Then examine carefully the HT leads and their connectors for signs of tracking, and then the distributor cap inside and the rotor arm. Any signs of tracking, then replace.

Plus the coil checks as above.

Losing my temper now

The new HT leads are fitted. I found a loose connection at the ignition switch and was quite convinced that once the HT leads arrived, the car would be perfect again - how wrong could I be?

She wouldn't even start! I double checked everything - all adjustments spot on, everything else is new apart from the carb.

Then I remembered I had some Easy Start in an aerosol. So I removed the air cleaner clips and the rubber pipe and sprayed for a couple of seconds straight into the air intake. Started instantly and ran perfectly and as soon as the Easy Start had been used, back to the misfiring and then it stopped.

Did it again to prove the point - same results. So what does tell me?

Fuel or ignition?

I have fuel and a spark - what the h*ll is wrong?

Angry and lost!

Ian