Newbie Warning. 1970 Fiat 500F. Purchased and taken into shop for tune up, overall general safety upgrade and road safety to enable licensing. While there shop recommended upgrading ignition to 123. After pickup at the shop the motor surged at speed and backfired at idle. The shop claims he thinks it's a sticking valve and claims it was like that when we brought it to him. (though I don't recall it ever backfiring during test drive and subsequent delivery to shop) I have tried to do the timing and put new fuel in. The surge is gone but the backfiring at idle is still there. I am handy with tools but in no way even a backyard mechanic. Any suggestions as to which direction I should go now.
:bang:

I don't know that engine, but generally I'd think it's a timing issue, although a valve that's not closing properly is a possibility.

Still, get a manual -- they're almost absurdly simple engines, designed to be taken apart at the side of the road by Italian housewives.

Being neither Italian nor a housewife so it's will take me a bit longer! I too beleive it is a timing issue and I am seriously wondering if perhaps the 123 distributer was installed 180 degrees out. Sure would like to see a photo of one installed on someone elses ride.

If the car was running perfectly before the distributor was replaced and now isn't, I've also got my money on mistiming. I also run a 123 distributor and have had no problems. They are not difficult to install and set up the static timing and once done, the engine should be started and run and the distributor rotated until the advance is correctly set.
I'm also not Italian nor am I a housewife
I'll post a photo of my setup tonight.
Chris

Thanks Chris! This is my Sweethearts toy and I would like to get it going right. Hopefully I can do that and then take the time to get the bodywork done to make it look pretty for her.

You've come to the right place - the bb is full of friendly types who have a wealth of advice and experience in and around these little gems.

Welcome and post a photo of your wee machine some time.

Chris

Good morning;
Whilst I would agree that timing is a probable cause of the back-firing, for the time it takes (not a lot), I would check the tappet settings. A tight inlet valve adjustment would cause a back fire as some of the 'bang' would be coming back through the slightly open valve. The settings are:- COLD--inlet and exhaust--0.15mm

It's always hard to tell at a distance and as we don't know what was done during the 'tune up', all I can advise is a methodical approach checking everything carefully and if possible, only making one major change at a time.

I can guarantee that you'll get good advice here, beginning with that from the hobbling one above

Here is the promised photo of my 123ignition distributor mounted on my 500 engine prior to rebuilding it as a 695. It won't give you a lot of information though.

Chris

Thanks guys! Nice shot of your engine bay there Chris. Don't think I will ever get this one that clean. My Lady wants it as a daily driver in the summer and not really a show car. She had a 1973 VW Bug but it was in my shop when it burnt down in Nov 2012. I am heading out there now to see what other kind of trouble I can get myself into. Here is a copy of the paperwork the shop gave me listing all they did.
In case you're interested, here's what the mechanic did for the tune-up and safety:

To inspect and check over for Safety Inspection and carried out relevant work. Carried out and Fitted new:-
Front Kingpin assemblies due to worn.
New Wiper Blades due to split.
Replaced Steering box assembly due to leaking oil.
Renewed Steering Idler System due to badly worn,
Renewed Brake Master Cylinder and fitted 4 new Wheel Cylinder and bled Brakes.
Changed engine oil, Spark Plugs and Valve Cover Gasket, checked and adjusted Valve Clearances.
Fitted new electronic ignition distributor, renewed ignition leads.
Renewed fuel pump due to leaking and pumping out oil.
Rebuilt carburettor with new gaskets etc and cleaned.
Fitted new fan belt.

Parts

2 King pins
Steering Knuckle Bushes
2 Wiper Blades
Steering Box
Main Brake Cylinder
Stop Lanip Switch
2 Wheel Cylinder (Front)
2 Wheel Cylinders (Rear)
Air Filter
2 Spark Plugs
Valve Cover Gasket
Electronic Distributor
Carb Kit
Fan Belt
Shipping and Duties etc.
Shop Supplies
Brake Fluid
Safety Inspection

In: Help setting ignition timing on Fiat 500 F thread. In post #3, Chris, you say that when you are 10 degrees of TDC the rotor should be pointing towards the engine block. Mine points away. Might that be the problem?

Hi CS welcome to the forum. I bet that was quite a big bill that the shop gave you?

Regarding the timing. It is quite easy to set the timing 180 degrees out, by putting the distributor in incorrectly but the car wouldn't even attempt to fire.

When you rotate the engine, I tend to stick a 17mm spanner on the bolt on the end of the dynamo to rotate it, a full rotation of the timing marks will result in the distributor/rotor arm rotating 180 degrees so when it is pointing towards the block it will line up on the distributor cap with HT lead 2 and will provide a spark to ignite cylinder 2. Rotate the engine 360 degrees again so that the timing marks are again lined up at 10 degrees BTDC and the rotor arm will have rotated 180 degrees and the rotor arm will point the opposite direction and line up with HT lead 1 on the cap. It's because both pistons go up and down together. You should statically time the timing with the rotor arm pointing away from the engine on cylinder 1.


Static timing cylinder 1. Rotor arm pointing away.


Cylinder 2 rotor arm pointing towards block. Ignore the marks on the belt it is the ones on the back of the flywheel.


I hope this helps.
Tony

CsFiat said:

In: Help setting ignition timing on Fiat 500 F thread. In post #3, Chris, you say that when you are 10 degrees of TDC the rotor should be pointing towards the engine block. Mine points away. Might that be the problem?

Click to expand...

It could point either toward or away from the block - my error in that post, sorry. The important issue is that the plug lead from the distributor cap fires the correct cylinder. If your rotor is pointing away from the block that is OK so long as that lead goes to the cylinder on the compression cycle. As Tony states above, if your rotor was 180 deg out, the engine would not fire at all.

They did adjust the valve clearances so that will be worth rechecking (engine cold).

I don't know why they ditched the entire steering box when it may have only needed a new seal and gasket. Being Canadian, I'm guessing that you have a LHD 500 because RHD steering boxes are like hens teeth. Maybe LHD boxes are cheap.

And the fuel pump was discharging oil ...

Let us know how you get on.

Chris

Okay, so Tony's answer basically eliminated the timing problem. (and yes that was a big bill they handed me) I find I can't get the RPM anywhere near 1200 before the backfiring starts. I guess judging by the comments from The Hobbler comment that the tappet settings are the next thing to check. Can one take the valve cover off without having a new gasket at hand or is it better to wait and order one.

I doubt that anything he did was cheap as the final bill was anything but 'light'. I did a bit of work today before heading out to run errands in the big city but had no luck at all. It seems to run fine above 1200RPM but does not like to wander below that at all. I guess valve clearance is next.

Okay Chris and Tony, I re-read your posts and I have this question. On my 123 distributor cap, (as received from the mechanic), the post marked 1 on the cap has the lead that goes to spark plug two and vice versa. Does that make any sense?

You can remove the valve cover and reuse the gasket if you are careful and if they haven't coated both surfaces with some sort of 'adhesive' sealant.

I just checked my distributor position and have posted a few photos. When cylinder 1 is about to fire, the rotor points nearly parallel to the block. This is the final position where I got smooth idle and acceleration. My engine idles at 800rpm and the 123 is setup for standard advance and yes, the engine was rebuilt correctly.

Prior to the rebuild, the ignition leads were aftermarket and quite long so it was easy to interchange them. Now I have the post marked 1 going to cylinder 1, though it doesn't really matter so long as the cylinder nearing the top of the compression cycle is about to get the spark.

Sorry to add to the confusion,
Chris

Okay Chris, now you have really messed me up regarding the distributor cap as it appears now that the lower section faces the rear of the vehicle (hence one can clearly read 123 Ignition) and your cap is running parallel to the engine block! Sorry if I am a little slow on the uptake, as I said at the very beginning of this thread, "Newbie Alert"! (oh and not much of a mechanic either!) By the way, mine base has the label in the back and the cap runs perpendicular to the block.

Put the distributor out of your mind for the moment and go back to the basics.

Was the car running (idling, accelerating etc.) OK prior to their tune-up?

Do you still have the original distributor?

Check the valve clearances with the engine cold.

Set up either the 123 or your original distributor according to the manual. No manual? You need to invest in one - they are cheap and worth the money.

You may need to lean on a mechanical mate - I'm spoiled for choice as my elder brother and one of my brothers-in-law are both very good mechanics and they live close. They like big V8 yank machines and are constantly poking fun at my love affair with small Italian cars. Nevertheless, they have been a big help over the years and I have learned lots from them.

Once all of the static mechanical stuff has been checked, then move on to the distributor itself.

Chris

PS: Nice little car - like the number plate

Have a manual, don't have the original distributer, yes it ran well before 'tune-up', live out in the boonies in my wife's end of the country with no mechanical mates to rely on.

I am planning on checking the valve clearances this morning and I found the instructions for the 123 online so I will try that after the valves.

As to the number plate my Ladie's VW she lost in the fire was called DaizyBug. She likes to name them something special.

Well, found out the gasket is glued on so I will have to wait until I can source a new one before I can check the valve clearance.