Fuel Vapourisation?

[David Morris]

Hi there,

Now that the weather is really hotting up, I had an unfortunate experience today, which if I am honest I have had once or twice before.

The Javelin ran well on a trip of around 6 miles to the local supermarket , and although it was hot weather, the temperature on the gauge did not get over 75°C. Parked up and did the shopping, as you do.

Coming back to the car about half an hour after arriving, it absolutely refused to start. Not a peep! I went through the normal checks, a good spark was there and I took off the filter bowls. I would say that they were not entirely full. Empted them out and checked the jets while I was there, everything OK.

Decided to let the engine cool and went to read a magazine in the supermarket. Came back after about 20 mins, pumped up the fuel into the bowls with the manual pump primer, and she started immediately! My diagnosis was fuel vapourisation. Was this correct?

If so, can anyone give me a tip for overcoming this. I had recently filled up with a different fuel and I have heard that modern unleaded fuels are more prone to this than older mixes. Is this true? Do types of fuel vary?

I have wrapped the exhaust pipe that goes between the two heads with heat tape to try and keep the general engine area cool.

Would an electric fuel pump help? Another symptom is that she is not exactly willing to start from being left for a few days. Priming the pump manually helps, but a quick squirt of Easystart gets her going first time! I have recently rebuilt the pump with a fresh gasket and valves.

Any help would be gratefully received.

All the best,

David

[Keith Andrews]

I am no expert on Javelins
It was/is the peactice of manufacturew to have a non heat conductiong space between the inlet manifold and carb. Conduction of latent heat to the carb thu this route is the normal cause for vaporisation of fuel.

I do not believe there is enough latent air conducted heat from manifolds and engine, in the engine compartment to cause vapourisation in carbs.
I nelieved so many yrs ago...then was shown by an old school mechanic, who sat a carb with fuel in, on spanner on the an engine block.
He explained issues 'vapourisation' crop up on older engines/components.
Can be traced back to worn butterfly bushes, incorrect mixtures, and other air leaks....also a spark plug worn or damaged (dropped on the ground) on installation.

U say u had low fuel level in the bowl...the jets are at the bottom, this will not effect fire up... a low fuel level will it will effect hi load situations and hard cornering

it absolutely refused to start. Not a peep! I went through the normal checks, a good spark was there and I took off the filter bowls. I would say that they were not entirely full. Empted them out and checked the jets while I was there, everything OK.

A quick 'fix'...carry a aersol can of Ether 'engine start'.
Check if have spark...yes
Squirt into carb, and get a fire, but reduses to start, a fuel supply problem.
If there is fuel in the tank, pump working, then the engine will fire up, maybe will take a 2nd shot of gas. No firing then bad spark.

If flooding occurs or is the issue, press the accelerator gently to the floor, and hold there...turn engine over till fires...Do not lift accerator between turn overs...what ineffect u are doing is using the engine as a pump to pass access fuel right thru and out of the engine, and re priming with a good fuel mix

[Keith Andrews]

Pat has reminded me of another "long Shot"
Replaced the coil recently?
A very common issue with boats stuck out on the Auckland Harbour...
They head out, then just die...will not fire but have spark and fuel...
Sit around for a while, then presto off again , then dies
Same again.
They have a 6V coil on a 12v system.
A 6V coil on a 12v system needs a ballast (resistance wire) or a ballast resistor (a ceramic block thing) in the circuit after the ign switch.

Sometimes a change in capacitor is also required to prevent premature burning/wear of points when changing removing a 6V ballast system on 12v battary coil to 12v coil.

[Tony Fearn]

Hi David.

A wise man once told me that, in the pre-war cars at least, over use of 'Easystart' might just blow a hole in the top of the pistons, so be careful.

Tony.

[Keith Andrews]

Yes....
The issue arises when ppl have a problem, and dont fix the issue
And they use an intial squirt then keep squirting to actually run the engine on ether rather than petrol...This isa in effect running the engine on extremmely hi octane, hot burning fuels AND WILL Cause DAMAGE.

Used occasionaly As it was intended for easy START...a 2 sec squirt, climb in the cab, fire up is not enough to cause damage for a couple of intial fire cycles.
Mis use, over the decades was produced a misconception of the product.

[David Morris]

Hi all,

Many thanks for all the advice. I was crusing around the Internet last evening and found the following that seems to describe my situation exactly :-

'Fuel vaporisation.

After an engine is shutdown, the temperature of its various components begins to stabilize; the hotter parts such as cylinders and oil cool, while other parts heat up due to the lack of air flow, heat conduction, and heat radiation from those parts of the engine which are cooling. This heat soaking is worse from 30 minutes to one hour following shutdown. During this time, the fuel system will heat up causing fuel in the pump and lines to "boil" or vaporize. During subsequent starting attempts, the fuel pump will initially be pumping some combination of fuel and fuel vapour. Until the entire fuel system becomes filled with liquid fuel, difficult starting and unstable engine operation will be experienced'.

This describes what happened to me in a nutshell!

I have electronic ignition and the spark seemed OK in the bright sunshine, so I suspect my problems seem to stem from fuel. I also found that different makes of fuel apparently have different vapouration levels. The national standards for this seem to allow quite considereable variations between brands. Perhaps my filling the tank with a different brand from usual has introduced a problem?

Anyway, I suspect the mechanical fuel pump may be a contributory factor. My Javelin's rather sluggish cold starting performance may mean the pump's valves are not too good, and this might be worsened when the fuel is nearly vapourising after standing on the hot tarmac. How do Jupiters get on with electric pumps? Do they ever suffer from fuel vapourisation, especially in the more traditionally hot areas of the world?


All the best, and thanks for all your help,

Regards,

David

[Keith Andrews]

I agree with PAt, look else where

After an engine is shutdown, the temperature of its various components begins to stabilize; the hotter parts such as cylinders and oil cool, while other parts heat up due to the lack of air flow, heat conduction, and heat radiation from those parts of the engine which are cooling. This heat soaking is worse from 30 minutes to one hour following shutdown.

This is normally a issue with cast iron blocks and manufolds that retain heat for longer periods...in engine compartments that have liitle head space. Flat AL engine blocks are not prone due to the greater spread of area that heat retaining parts cover.

For vapourisation to take place, the engine would have to have been run really hard AND HOT for long periods, Steel fuel lines run right next to, if not actually touching exhaust manifolds.
Vapourisation in a fuel pump maybe possible with a worn faulty pump, a pump in good condition and no air leaks before it...no cant see how even if vapoiisation would cause an engine not to start...unless the rear fuel lines are steel and run right next to and above the exhaust pipe.

A hot day...hot days are also falsly blamed for all sorts of things, from running hot to vapourisation...Again if these things occur on a hot day, thats a sure sign a problem with cooling system is present...Dirty, leaking, or partly blocked.

Yes modern fuels do have some more volitile components, like toluene..
But it is not enough to cause the fuel boil...

During this time, the fuel system will heat up causing fuel in the pump and lines to "boil" or vaporize. During subsequent starting attempts, the fuel pump will initially be pumping some combination of fuel and fuel vapour. Until the entire fuel system becomes filled with liquid fuel, difficult starting and unstable engine operation will be experienced'

.
It takes very little 'new' fuel thru the pump into lines to very quickly reduce temps in the lines..removing Any vapourisation if it did exist, carb drops in temp almost instantly.

This describes what happened to me in a nutshell!

So does what Pat says....
And fuel pump in poor condition, a air leak befiore the pump, a starter moter that has been over heated with poor solder joints on the armiture causing high resistance when hot, a condensor in bad condition, hi voltage coil on std 6 or 7mm leads, inlet manifold/carn butterfly leak, poor timing/stuck advance, flooded engine, crap in the carb/line and tank filters.

[David Morris]

Hi there,

Thanks for all the advice. However, I have probaly misled some contributors by using the word 'sluggish' when starting. A better description would be that she is reluctant to burst into life after being left standing for a few days. The battery and starter moter turn her over fine, so no problems there and she starts immediately again during use, once you have awoken her from her slumbers. The electronic ignition gives a good fat spark too.

I don't think this is caused by water getting into the cylinders either, as you usually get firing on less than four pots to begin with when this is present. She is just giving the symptoms of being empty of fuel until this arrives, and then she bursts into life.

Previous Javelins have been the same, and were totally cured by giving the fuel pump a few goes with the hand primer before trying to start. It's just that doing the same to my present Javelin does not give the same result, and hence my suspicions that all is not well with the fuel pump.

Thinking back over the problem and all the advice I have had, I still feel I had a nasty case of vapour lock and need to sort this out asap.

Many thanks,

David

[Keith Andrews]

She is just giving the symptoms of being empty of fuel until this arrives, and then she bursts into life.

I would be looking at things like
1/crud build up in the fuel lines
2/Air leak or cracked fuel line
3/Fuel pump Damaged diapham and or non retturn valves
3/Blocked fuel pick up and or fuel filters
4/Damaged carb gasket
5/carb float valve bad seats

If these things have not been rebuilt for a long time, a combo of them

From an ex hot rodder's point of veiw...
If the lines/pump etc are old, we would simply pull the whole lot from inside the tank to carb out...replace/rebuild and forget for another 20 or 30 yrs...
And yes I know, many do not have the tools, workshops to make parts or carry out this work themselves, so I do speak from the piont of veiw to being able to do so

If you run the car around a few miles, kill the engine and coast to a stop, pull the plugs, what do they read?

[Forumadmin]

When hand priming the fuel pump you should hear the fuel squirting into the float chambers. After about 4 primes you should feel resistance. That is assuming some fuel has evaporated from the chambers.

It could be that the fuel is not vapourizing correctly; are the chokes working?

If left for more than two weeks the fuel in the carbs looses its high volatility components; so may take that extra bit to get started.

[David Morris]

Hi there,

I was reading the Spring issue of Practical Classics today and there is an interesting letter on page 90 from an owner of a Morris 8 with apparent fuel vaporisation problems.

In reply, the magazine mentions that petrol companies produce different blends of fuels to suit the weather. In winter, they apparently market fuels that vaporise more easily and conversely in summer the fuels are less easily vaporised by an alteration in the blend recipe. The article argues that running a classic with the 'winter' blend of fuel in the tank could cause vaporisation difficulties on subsequent unexpectedly hot days. This might be the case if you have not done many miles since filling up in winter and start using the car in the warmer weather, or perhaps, dare I suggest, if the petrol companies have been caught out by the current unseasonal heatwave?

To be fair, the PC article does then suggest several other factors on a vehicle that might just as easily cause the effect noticed by the Morris 8 owner. These include many of the very useful tips already provided by the Jowetteers in this thread. However, I thought the fuel blend vs weather was an interesting observation.

All the best,

David