There's probably a post on this somewhere but I thought I might "cast the net" to see what I get so to speak...
My 500 (650cc conversion) won't start when the engine is hot. Checked spark ok, smells of fuel if I keep cranking. Starts great when cold, idles fine.
But after a long drive, I stalled it at a set of traffic lights and it wouldn't start. If I wait 5-10 mins or so it will fire up. Checked the compression all good. Not running points or condensor, as I have a hall-effect Hot-Spark ignition points conversion. So should be better and reliable.


I'm going to check the valve clearances next, then replace the coil. Does anyone have any suggestions that I may have missed....?
Heat soak? Vapour lock as I'm running 98 octane., but I can clearly smell fuel if I keep it cranking.

For an engine to run you need spark & compression timed correctly and a fuel/air mixture in the right proportions.

You have spark.

You have checked compression and are checking valve clearances.

The car starts and runs when cold so presumably the timing is OK.

My only thoughts are to things that malfunction in the heat of an engine bay.

They are electrical bits and pieces - condenser (you don't have one), coil (these definitely play up) etc. and fuel delivery. The pumps either work or they don't so it should be OK. However, the IMB carbies are renowned for playing up in the heat. It may need a rebuild, new float, new bakelite mount etc.

Chris

Yeah, thanks Chris. Carb was rebuilt, spacer is new as is fuel pump. Whole engine is brand spanker. The old previous 500 motor ran fine (just gutless) and never had this prob. I'm hoping its valve clearances and/or coil. I'll keep you posted.

It's always difficult to diagnose these at a distance. replacing the coil and checking everything else is a good start.

Let us know what happens.

Regards,
Chris

I would check the following, listed in order of probability:

1. Ignition dynamic timing (timing while engine is running at idle speed).
2. If using a Weber 28 IMB make sure the fuel enrichment piston "choke" is returning all the way back when choke lever is returned to off position. Cable will need to be adjusted.
3. Fuel mixture when hot.
4. Idle speed setting. Too high can make hot starts harder because throttle is held open too much.
5. Try using a lower octane petrol. Unless your compression ratio is up over 9.0/1, higher octane petrol is harder to ignite.

John

John and Spiderman, I find that when hot it's best to have the throttle down about halfway for hot starts, like you would on a motor scooter.

All good ideas....but its difficult to pin point the problem because by the time I've faffed about checking coils, idle jets, timing etc., the engine has cooled down considerable enough for it to start.
Its just going to be a process of elimination......that's why I asked if anyone else has had the same/ish sort of issue.

I have the same issue, please post if you find a solution.

I would say vapor lock. I use to have the same issue and when I installed an electric pump the issue went away but now I am on here looking and posting because I have another "Fuel" issue. haha
Feel free to look at my post and see if you can offer any ideas on my issue.
Hope you find a solution soon.

Hi there,

I don't come on the forum very often as it's my son who has the 500.
I notice that you have fitted a Hot Spark contactless system. Did you retain your old coil. Because the Hotspark is a solid state switch, it breaks the primary to the coil quicker and "cleaner" than a points system. Because of the faster delta change in the magnetic field as it collapses, it produces a higher voltage in the secondary. Also the solid state device has a much lower resitance than the points so it can saturate the coil better producing a higher energy spark. If you have an old standard coil and it's near a heat source it could be breaking down as it gets hotter from the higher duty cycle of a solid state switch.
I would always recommend fitting a High Voltage coil such as a Flame Thrower or a Lucas Sports which are built to withstand higher voltages and decent silicon HT leads when you convert to electronic ignition.
You can get "Electronic" coils such as the Bosch Blue High Voltage/High energy coil but I think it is probably overkill for a 500/650/695cc car.
The fact your car dies suddenly would point more to an electrical ignition problem than fuel evaporation which usually manifests itself by stuttering as the mixture weakens. But then again ...
Best of luck
Richard

Question...When it dies does it do so slowly or suddenly?

Evening. I have been having the same issue of not hot starting. I am looking into many of the solutions I have read here but I wanted to test an idea and got this answer. While it would not start when it is hot I push started it with no problem at all. Started right up when push started. I hope this provides some possible insight. Any ideas?

Thank you!

124spiderman said:

......... Not running points or condensor, as I have a hall-effect Hot-Spark ignition points conversion. So should be better and reliable..........

Click to expand...

UPDATE: "Hot-spark" was a "No spark".

Try again or have you got the point(s)?

Chris

Aloha. My name is Kerry and I have a 69 Fiat 500 in Hawaii. The car has a rebuilt 650 engine and tranny. I am suffering from the same hot start problem that seems to be getting worse as I contine to track down the problem by spending time and a lot of money on parts. I have a new carb, plugs, wires, fuel pump (and a electric secondary). I do have a Hot Spark ignition with a standard coil so I am intrigued and excited about Mattsdad's suggestion. I was otherwise thinking vapor lock as after I iced the carb, the car restarted (could just be everything cooled off?). I am ready to wrap the exhaust and even rig up a carb fan. Any body have or know how tp cure the problem - it is zapping the pleasure out of my Fiat 500 experience. Kerry

TonyAllenORL said:

Evening. I have been having the same issue of not hot starting. I am looking into many of the solutions I have read here but I wanted to test an idea and got this answer. While it would not start when it is hot I push started it with no problem at all. Started right up when push started. I hope this provides some possible insight. Any ideas?

Thank you!

Click to expand...

Hi all

If this is the case then perhaps the problem is the starter drawing too much current when it's hot, thereby restricting available current to the coil, especially if that is also hot. If I understand it the starter on the 650 is located differently to the 500 (is it engine or gearbox/bellhousing driven??). The only difference between push start and electric start is the starter motor.

Thoughts?

J

Konrod said:

Hi all

If this is the case then perhaps the problem is the starter drawing too much current when it's hot, thereby restricting available current to the coil, especially if that is also hot. If I understand it the starter on the 650 is located differently to the 500 (is it engine or gearbox/bellhousing driven??). The only difference between push start and electric start is the starter motor.

Thoughts?

J

Click to expand...

J starters can get gummed up and not spin as freely as they should and hence when attempting to start they will draw more current. It used to happen on mine and as a temporary measure a sharp whack on the outside with a spanner would free it up and allow it to spin again.

However having said all that hot starting is such a common problem on 500's that it would mean that a lot of 500's suffering from issues with starter motors which I really can't see.

In my experience hot starting issues are quite often down to incorrect tappet gaps, coils or condensers breaking down when hot. The engine does run quite hot so I think there is always going to a degree of fuel vaporisation which is inevitable. On the later Polish built 126's they added a manual flap on the fan housing to allow a blast of cooler air to be directed onto the carb to assist. I guess they wouldn't have done this if they hadn't recognised there was an issue.

Tony

Interesting point about the flap on the later 126's. I'd agree fuel vapourisation is likely, supported by comments about hot starting with the throttle half or fully open, as well as the electronics being heat sensitive - this isn't limited to 500s.

The point I was making was in response to the comment that bump starting enables the car to start when hot - if so then it can only be starter motor related as the rest is constant. It is quite possble to be a common problem - how many of us have new starter motors? Even new re-builds will generally transfer the old ancillaries over, and that makes them 40+ years old - brushes may be new but the winding assemblies won't be. I can't believe this was a generic or even common problem when they were new in Italy so it has to be age related.

Having this read lots of the threads (i have the problem as well:bang, I think the reality is that there is no single magic bullet. They run on the edge when hot so any degradation anywhere will have an impact, and degradation in any of the fuel delivery or ignition components will have the same symptoms.

Having said that, next time I have the problem I'm trying a bump start just to see what happens.....

No I agree with everything you say but the one thing that has changed that everyone overlooks is fuel. Modern unleaded fuel burns hotter, therefore there will be a tendency for the whole engine to run hotter.

Our old workhorse engines were designed for leaded fuel, unleaded fuel tends to require the timing to be retarded a few degrees to run most efficiently.

Most people when they encounter hot starting problem will naturally go back to basics, checking the timing being one of the first things and I bet you 99% of people will set it at what the manual says 13°BTDC. Doing the timing with a strobe light sounds like the ideal solution but in reality doing it by ear on a 500 is much better. My car runs about 2 or 3 degrees retarded, I think it is retarded I can't really remember, it maybe advanced but that's where it runs best.

Maybe next time you have the hot start problem slacken off the distributor and give it a tiny turn in either direction and see if it improves it at all?

Tony

Did you solve the starting problems? What about the valve clearances, did you check that?