Technical 1973 Fiat 124 Berlina Sedan inconsistent timing

[SeanLChin]

Hi everyone,

I just bought a 1973 124 special sedan. I have had a couple of issues that I could use some help with.

At low rpm the timing is super in consistent. When I used a timing light the timing mark jumps around. At high rpms the timing mark on the crank pulley stays advances and is consistent.

The engine has also been dying at stops and after I give it a lot of throttle.

Yesterday, I drove the car around and the and it was idling at like 3,000 rpms, but then after a 5 -10 minutes it went back to low idle speed and was really rough.

The car feels pretty good at speed, but it won't idle right and dies at stops.

Also how hard is it to switch to electronic ignition?

Any advice you have to fix this would be greatly appreciated.

Thanks,
Sean

 

[varesecrazy]

rconlon

 

[F123C]

A worn timing chain can cause the ignition timing to vary.

Also wear in the drive gear that drives the distributor from the camshaft.

Check that the mechanical advance unit isn't worn, hasn't got sticking bob-weights or broken/detached return springs (there are 2 springs, one should have free-play, the other should not). Iirc, this advance unit is just under the large circular rotor arm, so no need to remove the distributor to check it out, (just remove the distributor cap and unscrew the rotor arm). When refitting the rotor arm, note that there are 2 locating pins underneath, 1 round, 1 square, so it'll only fit one way round.

The standard ignition system (points and coil) is quite adequate if maintained.

Fitting an electronic ignition system to the distributor won't cure timing scatter if it's being caused by any of the above problems.

I don't know if the U.S spec 124 Sedan has a manual or automatic choke, but your problem with high idle speed sounds like an Automatic Choke problem. You could try running the engine with the air cleaner unit removed to check if the choke flap is opening fully (i.e. is vertical) as the engine warms up. The choke has a connection to the throttle (accelerator) linkage to provide a fast idle when running on choke - so if the choke stays on, the idle speed is very high, but 3000 rpm is crazy high, 1500 is plenty. Check also for any sticking linkage and that you have a little free-play in the accelerator/ throttle cable.

If your choke is manually operated, check for a sticking linkage, and sufficient free-play in the accelerator cable.

An air leak can also cause a high idle speed, but this won't cure itself, so I'd concentrate on the choke function.

Varying/incorrect ignition timing won't cause the idle speed to hang up at 3000 rpm.

The erratic idle speed after a run might be due to the idle speed having been incorrectly adjusted, someone might have adjusted it on the choke fast-idle speed adjuster screw instead of the idle speed screw at the throttle stop.
To check if this is case, with the choke fully off i.e. choke flap in the vertical position, there should be a small gap between the fast idle speed adjuster screw and the stepped cam plate that it engages with to raise the idle speed when on choke.

Al.

 

[SeanLChin]

Awesome. Thank you so much.

The high idle was caused by sticky choke linkage (manual choke), and the roughness was caused by a vacuum leak on emissions related stuff. I plugged the leak and now the timing is pretty consistent. After I fixed that stuff I adjusted the idle screw, and now it's pretty good.

I think next, I'm going to rip out all the emissions equipment. I live in California and if your car is pre-1976 you don't have to do emissions testing.

Thanks again,
Sean

 

[F123C]

Hi :wave: Sean,

Thanks for the update and I'm glad to hear you've sorted the problems.

I had a number of 124 Sedans in the 1970's (I worked as a Fiat dealership Mechanic) and thought they were great cars, imho better than what Fiat produced subsequently - if I could find a rust-free one over here, I'd buy it in a heartbeat! (I've also had several 124 Sport Coupes ). By 1973, i.e. your model, Fiat had ironed out most of the little niggles. In Europe. the 124 Sedan was voted 'Car of the Year' when it was first introduced.

The British TV Presenter, James May, recently did a series called 'Cars of the People' - one episode covered the long and successful history of the 124, incl. after the design was sold off to Russia, the total of all variations of the 124 produced was something crazy like iirc 40? million units . If you're interested, you might be able to find this series on YouTube?

After I had written my above post, I remembered that afaik all the 124 Sedans had a manual choke, it was the subsequent 131 (Brava in the USA?) that had an automatic choke - another retrograde move by Fiat imho. Sorry if I gave you a wrong steer. :doh:

It's always great to find out what was actually causing the issues and how they were rectified. This way, we can all potentially learn something, plus it can be invaluable to anyone who does a search before posting a query, to have as many real-world causes of issues as possible to check out.

Regards,

Al.