Starts good on a cold start. As it warms up, it

Sounds like your fuel shut off solenoid isn't doing its job. I'd replace that first then adjust the choke if it's still not running right.

That sounds like a fuel/air mixture problem.

Just to confirm .. it is a carburettor, not fuel injection?

As a general rule of thumb (with carburettors..) if it backfires through the exhaust/muffler .. the fuel mixture is too rich.

If it backfires through the carb/air filter, the mixture is too weak.

It could also be a 'sticking' float in the carb.

When an engine is cold the fuel is rich .. lots of fuel .. that's how a choke works.. However, when the engine warms up a rich mixture causes problems. The car may splutter and stall, run sluggish or cut out.

a bad engine coolant temperature sensor will cause cold no start conditions.your coolant sensor main sensor during cold start condition because when engine coolant cold PCM will cause rich fuel mixture for cold start up when engine coolant and oxygen sensor warms up cause engine goo in close loop lean mixture.but coolant sensor is the main information sensor if bad it will cause many problems.

sounds like the choke is sticking closed or needs to be adjusted and the carbon build up from this condition is glowing red hot in the combustion chamber so when you turn off key the fuel keeps lighting off and you have run on. that is if the vehicle has a carb if it is fuel injected then i would check to see if injectors are leaking some older FI. cars had cold start valves and they went bad all the time

I am going to guess at the easiest first .
I will attempt to explain my reasoning without going into it so far as to bore anyone...

Coolent tempreture sensor ;
When the car is cold it starts fine , as it warms up (coolent temp sensor) the ECM is signaled to decrese the rich fuel mixture (choke).

Test coolent sensor for variences in reading with an ohm meter to verify the sensors condition.


Plugged fuel filter;
Cold start , fuel is sedentary allowing particles to settle (paired with the enrichened fuel mixture of cold start), Then when warmed the particles are clogging the filter and the fuel enrichment of the cold start is no longer helping the starving condition...

Its hard to diagnose with what little information you have provided.
If you are ghetting a code , take it to the nearest AutoZone and get a free diagnostic done.

The computer runs the fuel mixture rich when cold and then leans out as it warms up into closed loop, a common problem is the regulator leaking, if you remove the upper part of the intake and then turn key on and watch for fuel leaks, another trick is to remove the throtlebody and use a light to see if fuel is puddling up on the top of the intake, make sure to dissconnect module connectors to avoid a false start or spark that will cause a fire, i would almost bet its the regulator, hope this helps,

for one thing the cabureter need rebuilding, and the choke repaired, fix that exhaust leak, most of what you describe relates to fuel, also run some combustion cleaner through the engine, its been running rich and there are deposits causin dieseling when you shut it off, all of this is easy for an older mechanic

Hello,
The car may be hard to start because it may need a normal tune-up. If the spark plugs are pretty used, they will slowly stop burning as much fuel because the spark slowly gets lesser and lesser. On a cold day the fuel is harder to ignite with a small amount of spark.
Normal idle when its cold means that your cars idle is probably too high. If you lower the idle, the choke on a cold day will keep the idle a little higher until the motor warms and then it will kick back off. If the idle is too high, it will run very rich, smothering itself with fuel, and causing the idle to stay low. When the car warms, its creating better spark when its warm, and with the idle being too high its running at a fast idle.
The car wont start sometimes can be the cause of a few things. If the ground is bad on the fuel pump, it wont make a good connection sometimes for when you turn the key on, the fuel pump dont pump the fuel to the engine. Another one can be that your accessory switch can be loose going to the fuel pump. I think its your ground though. Good luck! Hope this helps.
Have a nice day. -Steve

If yours is a Mikuni carb, here's what I did to make my choke work manually on a 1986 Plymouth Voyager:

http://imhdd.ms11.net/CHOKE/choke.html

Your problem is more likely a distributor-timing problem, than a carburator problem. The richness of the fuel acts like a constant choke, and the car runs fine until it warms up.

Once the car is warm, try manually advancing the spark. If that helps, then take the distributor to a repair shop that can tell you if the vacuum advance is working properly.

Remember, the spark must be +10 degrees advanced when cold.

Good Luck