8 replies to this topic

[Banni]

Hi,
I'm a bit confused.
When I go to the Mini in the morning, even in the cold it starts with the choke on, and drives totally fine.
But if I turn off the engine and then try and start again it won't, unless I wait about half an hour in which case it starts fine!
Any suggestions?
Cheers

[tom1234177]

Coil or condenser has gone, check you have the correct voltage coming from the coil, and it isn't getting stupidly hot when the car is running, dispensor's are few quid worth swapping for a try.

Edited by tom1234177, 02 December 2011 - 11:09 AM.

[AVV IT]

It sounds like you might be "flooding the engine", (filling the cylinders with an excessively rich air-fuel mixture that cannot be ignited because the mixture exceeds the upper explosive limit of the petrol, sometimes even fouling the spark plugs.) Basically too much petrol is going into the cylinders to the point that it becomes too wet to ignite. This used to be a very common problem when all cars had carbs, but it's pretty much unheard of in modern cars since the introduction of fuel injection. The reason the car starts after half an hour or so, is because some of the petrol will have evaporated in that time allowing it to ignite again and for the engine to restart. Every time you try and restart it before this time, you make the problem worse by pumping yet more fuel into the cylinders as you crank the engine over in an attempt to re-start it.

Many things can cause and contribute to flooding, although it's most commonly caused by drivers who pump the accelerator pedal when trying to start the car. Other contributing factors include an or over rich fuel mixture, poorly adjusted/stuck choke, poor spark and the timing being out.

Edited by AVV IT, 02 December 2011 - 11:06 AM.

[liirge]

Coil or dispensor has gone, check you have the correct voltage coming from the coil, and it isn't getting stupidly hot when the car is running, dispensor's are few quid worth swapping for a try.

There is no such thing as a dispenser, however I have a feeling I know what you are on about, Condenser maybe....

When it refuses to turn back on have you tried to see if you get a spark at the plugs, to do this take a spark plug out ensure the HT lead is still attached and then rest it on the engine,ensure a good earth point (head stud) is touching the plug. Then turn the car over with the ignition on and see if the plug is sparking, if not you know its an ignition problem

Assuming it is:
OP
You haven't said anything about the car, such as model etc. I deduced that it was a carburetor model, however it is impossible to diagnose anything without knowing what type of distributor you have.

Assuming its not an electric pick up Dizzy, and it uses points, condenser and normal coil (not coil pack), it is a reasonable to deduce that heat is affecting something, The two likely things are the condenser and the ignition coil itself, however its rarely the coil, so go with the condenser - replacements are cheap and widely available from most motor factors.

.

Edited by liirge, 02 December 2011 - 11:14 AM.

[tom1234177]

Yes Condenser! sorry

Edited by tom1234177, 02 December 2011 - 11:09 AM.

[liirge]

It sounds like you might be "flooding the engine", (filling the cylinders with an excessively rich air-fuel mixture that cannot be ignited because the mixture exceeds the upper explosive limit of the petrol, sometimes even fouling the spark plugs.) Basically too much petrol is going into the cylinders to the point that it becomes too wet to ignite. This used to be a very common problem when all cars had carbs, but it's pretty much unheard of in modern cars since the introduction of fuel injection. The reason the car starts after half an hour or so, is because some of the petrol will have evaporated in that time allowing it to ignite again and for the engine to restart. Every time you try and restart it before this time, you make the problem worse by pumping yet more fuel into the cylinders as you crank the engine over in an attempt to re-start it.

Many things can cause and contribute to flooding, although it's most commonly caused by drivers who pump the accelerator pedal when trying to start the car. Other contributing factors include an or over rich fuel mixture, poorly adjusted/stuck choke, poor spark and the timing being out.

On an SU HS OR HIF carburetor pushing the accelerator on start up will not alter the mixture on start up enough to create a flooding situation, this usually only applies to carbs that have that feature built in. I would say if the mixture was too rich to flood the engine in this manner the OP would not have to use the choke to start his car in the morning.


Accelerator pump

Liquid gasoline, being denser than air, is slower than air to react to a force applied to it. When the throttle is rapidly opened, airflow through the carburetor increases immediately, faster than the fuel flow rate can increase. This transient oversupply of air causes a lean mixture, which makes the engine misfire (or "stumble")—an effect opposite what was demanded by opening the throttle. This is remedied by the use of a small piston or diaphragm pump which, when actuated by the throttle linkage, forces a small amount of gasoline through a jet into the carburetor throat.^[4] This extra shot of fuel counteracts the transient lean condition on throttle tip-in. Most accelerator pumps are adjustable for volume and/or duration by some means. Eventually the seals around the moving parts of the pump wear such that pump output is reduced; this reduction of the accelerator pump shot causes stumbling under acceleration until the seals on the pump are renewed.

The accelerator pump is also used to prime the engine with fuel prior to a cold start. Excessive priming, like an improperly adjusted choke, can cause flooding. This is when too much fuel and not enough air are present to support combustion. For this reason, most carburetors are equipped with an unloader mechanism: The accelerator is held at wide open throttle while the engine is cranked, the unloader holds the choke open and admits extra air, and eventually the excess fuel is cleared out and the engine starts.

Source: Wikipedia,

Edited by liirge, 02 December 2011 - 11:13 AM.

[Sprocket]

Modern fuel injected engines still flood on cold mornings if you just move the car from the drive onto the road, and you don't let it warm up before switching it off. I know of several modern cars that have done this. The flooding problem does not magically dissappear because of fuel injection, it's likelyhood is however reduced.

[ace01]

Another potential cause is vaporisation of the fuel in the float chamber. When the car is running the movement of the fuel combined with movement of the car would keep the heat from causing a problem. However, when you stop, the heat from the now hot exhaust can vaporise the fuel in the float chamber/jet and cause the problem described.

As has been said a few more details of the carb would be good, additionally do you have a heat shield between the carb and exhaust manifold?

[canadiankev]

Does your car turn over and just not fire up? I had a problem where when the engine was hot it wouldnt start and within minutes the battery was flat, it turned out when the engine was hot the starter was drawing to much power and flattened the battery but if engine was cold it started everytime