Technical Greeting + a few questions

[Factotums]

Hello everyone and greetings from Bulgaria,

Me and wife always had a dream of owning a classic Fiat 500 and two months ago we managed to achieve it. We are the second owner of a 1971 Fiat 500L with 72k km on the clock. Our tiny spicy red pepper ( named him Peperoncino ) is one of the best decisions we've made. It is a pure joy of a car - every time I tinker with it I smile, every time I drive it - a grin.

Most of the bodywork has been completed already, so we got it as you see it - Rosso Medio. Only 1 problematic spot is left and that is the shelf above the engine which has rust where water gathers through the intake vent. I will redo the carpet cause they have ruffled and faded but all the rest is ok . Got a new fuel tank -old one was leaking everywhere.

What is not ok is the unsteady idle. Honestly the car was better off a week ago and progressively got worse but still driveable.

I have tried adjusting the idle according to the manual, screwed in the throttle till it is slight faster than engine rocking, then started playing with the mixture.

I have set the rocker clearances when cold today and the car became louder but noticeably quicker - there was zero clearance on both cylinders and all 4 valves - the gap is 0.15mm on all 4 now. Had to change the gasket on both carb and valve cover - worse thing to do since the old one broke into pieces and were stuck on the head.

I have set

The problem is kinda weird the engine rocks a bit (pivoting left and right), i have changed all the rubber mounts and the spring, the old one desintegrated. I start cold with choke on and all is good albeit loud, then gradually lower the choke but BEFORE it is warm with half choke on it cuts off on traffic lights if i don't keep slight revs up. When it completely warms up with choke off - it rarely cuts off or stalls, it just feels a bit more vibratey than normal.

I think I either have not set the mixture correctly or the ignition gap ( set it to about 0.45 ).

So the questions are as follows:
- what can cause that rather rough idle (without misfires at revs)
- is it normal for the engine to become louder after the rocker adjustment, sounds more rattly than before.

Any help will be greatly appreciated.

 

[Goldnrust]

Hi, welcome to the forum! I'm glad you're enjoying your 500, it looks lovely

Sorry to hear of the challenges, as I'm sure you're aware, classic cars are always a bit of a work in progress! haha.

It's to be expected that there's a bit more valve train noise when you have some clearance instead of none, especially when the engine is cold. It's not a quiet engine in general and mine certainly sounds like a bag of spacers when cold! That said, once the engine is good and hot, I mean after 20-30mins of driving, you'd expect those valve train rattles to have quietened down quite a bit. The adjusters are quite coarse, and it's easy for the clearances to shift as you tighten the lock nut down, so might be worth another check?

Ultimately slightly loose and rattly wont do much harm, apart from being noisy, but too tight a valve clearance can lead to the valves being held of their seats when the engine is hot, leading to temporary loss of compression and at worst damaging the valves or seats.

The symptoms you describe with stalling on half choke is similar to my car, which I believe is 'normal'?! I have the hand throttle cable installed, and use that to just hold the idle a little high till the engine comes off the choke.

For the idle mixture setting, you want to get the car good and hot, then as you say raise the idle speed just a little and then turn the mixture screw in 1/4 turn at a time. Each time you adjust it, give the car a few seconds to settle, maybe rev the throttle, see how it returns to idle. If when you turn the mixture screw in the idle sped comes up, keep going bit by bit till it starts to stumble/slow down and then turn it 1/4 back out. If on the other hand it immediately gets worse then try turning it out 1/4 turn at a time till you see no improvement in idle quality/speed. Then you can adjust the idle speed screw back down to a normal speed.

You mentioned changing the fuel tank, have you been through and cleaned the carb also? If the fuel tank was in poor condition it would be likely that some debris made it into the carb and could be blocking some of the idle circuit passages which would make it impossible to get the idle mix right no matter what position the screw is set.

Likewise the base of the carbs can warp, leading to a poor air seal to the manifold. It would be worth removing the carb and checking it for flatness.

On the ignition side of things, you're looking for a points gap of 0.5mm, and a spark plug gap of ~0.7mm. Ignition components are cheap and available, so it might be worth replacing some of them if you're unsure of their history. A member of here recently chased a difficult to solve problem down to a simple faulty spark plug! Plugs, leads, distributor cap, points, condenser, etc are all easy to swap out and test.

Hopefully that's plenty to get thinking about. With these basic olds cars it's usual something simple and easy when you find the issue... but somehow that doesn't make getting to the bottom of the problem in the first place any easier!!

 

[Factotums]

Hey,

The noise definitely quieted down at operating temp, the compression was fine when we measured it so I hope that problem was avoided.

When i had the carb off I checked if it is warped by trying to rock it on a table and it seemed completely flat BUT i was not that thorough and did not clean it after the tank change, honestly I am a home mechanic up to the point that I can do the required but i learn along the way sooo next step - cleaning the carb.

When I got it, it refused to start because of a blown condenser ( the flatbed guy reversed the battery ..... ) so I took apart practically everything connected to the ignition, replaced all condensers, checked the leads, fitted a new battery, cleaned the point, cleaned the spark plug but did not set the gaps to 0.7, they were 0.9 so i will do that as well.

Priceless input thanks a lot!

 

[Goldnrust]

It sounds like you’re on the right track.

Good news about the compression test, I didn’t want to mention it and scare you too much!

0.9mm is definitely too big a spark plug gap for an old fashioned points system, but I would expect that to show up at high load at speed, rather than in poor idle quality. Still it’s an easy and free thing to test.

Let us know how you get on when investigating the carb

It’s a very simple carb, you just need to keep track of where the various small parts go. Take pictures as you go to refer back to and if you get stuck I’m sure someone will be able to offer advice!

 

[the hobbler]

It sounds like you’re on the right track.

Good news about the compression test, I didn’t want to mention it and scare you too much!

0.9mm is definitely too big a spark plug gap for an old fashioned points system, but I would expect that to show up at high load at speed, rather than in poor idle quality. Still it’s an easy and free thing to test.

Let us know how you get on when investigating the carb

It’s a very simple carb, you just need to keep track of where the various small parts go. Take pictures as you go to refer back to and if you get stuck I’m sure someone will be able to offer advice!

The 500 (110) engine does have a habit of the valve clearances closing up, so now that you have got the engine running better, another check of the clearances (COLD) won't go amiss. As "Goldenrust" has already mentioned, both the carbs and the phenolic spacer have a habit of warping, so letting air bleed in and affecting the mixture. The best way to check, and rectify, this problem is to flatten them down on a sheet of fine "wet 'n dry" emery-paper (wetted with WD40 or a very thin oil, on a FLAT surface--glass or similar))---you might be surprised as to how much warpage there is on the base of the carb (and possibly the spacer). If you have had corrosion problems in the fueltank, there is always the chance that a small pice of rust has got caught in the carb, or the idle jet---this will also affect the idle adjustment. Goldenrust's description for adjusting the idle was good. Let us know how you get on---solving these problems can often help other members sort intermittant problems.

 

[Factotums]

Ok, so I did have some time today to quickly recheck the clearances and I overdid them a bit I guess - 0.2 instead of 0.15. Done correctly - much quieter now.

I will clean the carb over the next few days and report back.

 

[Noah500]

Welcome! 1971 500L - excellent choice

 

[RobertM]

I would also agree to cleaning the carb, I had problems with my fuel tank getting sediment into the carb and making it run poorly or sometimes not at all.

Typically what I did to clean it in a hurry was to remove the carb, pull the 4 screws out of the top plate, and blow everything out with a bit of carb cleaner without completely removing everything.

In addition to replacing the tank it might not be a bad idea to replace your fuel lines from the tank to the back of the car, there's only a small amount of bent metal line, and in the case of my car when I removed that section it crumbled in my hands. The entire fuel line took me ~2 hours to replace.

 

[Factotums]

A small update - fuel lines replaced with the tank.
Stuck read left drum - ordered full rebuild kits for all 4 sides, going after that problem next week.

The noise valves were due to higher than spec clearance ( i did set them at 0.15 BUT they had grime and sludge on them so that was more than 0.15)

Carb is off the car and ready for cleaning, it was warped but very slightly - still dragged it on some wet sand paper soaked in WD, completely flat now.

I will post pics and more updates in the coming week.