Fuel Vaporisation?

[MKTR]

Hi All,

I realise that there has been lots of discussion about fuel vaporisation and ethanol before and I have taken steps such as having HS6 carb shields, using E5 petrol, and opening the bonnet when hot.  However, I still need to crank the engine a few times after parking my TR4 before it will start - and as is often is the case it is fine when cold.

Some other symptoms are causing me to question if my issues are actually related to heat sink etc or if there is something else to consider:

1. The inline filter just before the carbs is always empty and I can see petrol spurting in when the engine is running. Even if I undo the pipe connections and prime the line and filter to full, it quickly reverts back to empty/almost empty after parking when hot.  It does not affect the running of the car but it seems odd to me.

2. I have a few drips of petrol under the rear SU carb after a run and the car cooling down again.  It shows no leaks on start up or when running.  I cannot tell if it is from the carb reservoir or the needle jet, but suspect reservoir.

Maybe it is all down to vaporisation and the build up of vapour pressure, but perhaps there may be something wrong with pump return valves or needle valves?

I have checked the needle valve and float seetings and there is petrol in the reservoirs, even after parking hot.

Grateful for you comments.

Mark

[RobG]

Hi Mark,

If it helps, my filter always stays full after running and petrol can be seen again at the next start.

I assume the fuel pump button valves keep the fuel in the lines, so I suspect your valves are letting it drain back.

RobG

[trchris]

Hi Mark

A few have fitted electric fuel pumps to help with this issue and because replacement mechanical pump quality is not good my filter also stays full if you have fuel in the float chambers it maybe another small problem (ignition? ) causing your bad hot start
Chris

[MichaelH]

+1 for mechanical fuel pump valve leaking back.

Michael H

Edited August 24, 2023 by MichaelH

[MKTR]

Thanks Rob, Michael and Chris - I think I will fill the lines and filter, disconnect from Carbs, and see if gravity drains fuel back down.  If yes then I can replace the valves and hope they are ethanol resistant.

Mark

[Z320]

Hi Mark,

the max level in the petrol tank is about 4 - 6“ higher than the carbs.

Your petrol filter on the front carb should stay full as long your petrol tank is full,

While the petrol flows back through the pump if the petrol tank is lower than 3/4 full.

The petrol can not built up any vapour pressure in the carbs or float chamber because EVERY float chamber is vented to the atmosphere.

Without the ventilation the carb/engine can not work.

A lot is told about problems of „air“ in the petrol supply, but this are flammable gases and the TR carbs are ultimative simple.

I see no reason why this should cause any restart problems, I guess there is another problem on your TR.

Ciao, Marco

edit: please notice this post , the max fuel level is only 2" higher than the carbs

Edited August 25, 2023 by Z320

[RJSTR4A]

Where's your inline fuel filter mounted?  If between the fuel pump and carbs, especially if between the thermostat housing and float bowl, I suggest you replace it with standard 1/4" fuel line.  This placement puts it aft of the radiator and over the hot manifold.  It is not stock either. The air gap in the fuel filter is perfectly normal. But, in that position it is hit with radiant heat from both sides. And the air gap permits the fuel to vaporize much more easily than if it was flowing through a continuous line sealed at both ends. 

Also, be sure the fuel line routed properly around the water pump and not touching any of the radiator hoses. 

Good luck.  

Bob

1966 TR4A - 23 yr owner

[Z320]

This is where my metal and glas „filter“ is fitted, only used as a gauge.

I expect it cools the hot petrol down, heated up before by the mechanical pump.

Just another theory?

Edited August 29, 2023 by Z320

[MKTR]

Thanks everyone - this has given me much to consider.

I filled up the filter and left it over the weekend, and lost no fuel to gravity.  I also tried to push the petrol back through the pump with a large syringe and there was firm resistance.  As such, I am confident that the pump and button valves are working fine.

The forum seems to have different opions about having an in-line filter between the pump and carbs, but I like the abilty to see if petrol is flowing and more confidence that fine particles are not reaching the needle valves.  So I guess that leaves me trying to protect the fuel line as best I can.  I do need to re-route the line to pass in front of the water pump.  I am still not finding the reason for a petrol drip under the rear carb though.

As to re-starting not being a fuel issue - I will need to check everything out again.  I have a new coil mounted away from the engine block, and I have points and condenser from the Distributor Doctor.  Anything else to consider?

Regards,

Mark

[stuart]

I dont like those inline filters.With the mechanical pump you have a gauze filter and a glass bowl below it for the sediment if any to collect in. If your getting noticeable sediment in the bowl then its time to change your tank.

Stuart.

[Z320]

I‘m with Stuart.

But I also like to see the petrol and cut out the mesh.

Because this metal/glas „filters“ are a fantasy product:

the mash is too narrow and already blocked long before dust is visible.

I wrote a post about my brakedown some time ago here at this forum.

Very simple: a inline filter is made to change and kick it in the bin - not to clean

Edited August 29, 2023 by Z320

[Michel Higuet]

For the air gap in the fuel filter I have the same and it is not a problem for me, Yes I filled the filter but the filter returned on his normal state with air gap.

 I had a few drips of petrol under the front SU carb from the connection of the jet to the float bowl, but to remove the choke linkage arm off the jet if you wrong slightly the jet to access the screw you tear the inner tube ( more breakable when old ) that's what happened to me.

Some sale you as replacement the joint in the float bowl as a simple O-ring, no good, the real joint is tubular.

I will fixe the jet to the float bowl and test it on the bench with petrol, then inserting the jet and fixe the bowl and twist no more the jet to fixe the choke linkage arm.

If the joint is ok maybe only tighten the nut is maybe sufficient.

 

 

[MKTR]

Many thanks to everyone who has contributed so far.  What I have done before/since is:

• have SU heat shields fitted
• replace the fuel pump diaphragm and valves with new ethanol resistant parts (just in case)
• re-routed the pump to carb fuel pipe in front of the water pump and wrapped with heat shield fabric
• changed all 8mm and 6mm rubber pipes
• replaced in line fuel filter
• checks all carb hose links and float valves
• changed my points condenser again

The good news is that I appear to have solved the drip under the rear carb and suspect the 6mm hose was cracked slightly.  Starting also seems slightly better when hot, but it is not like it is when the car is cold.

The bad news is that I cannot seem to keep a good level of petrol in the in line filter.  It is fine when just idling on the driveway, but when viewing after a good run out, the fuel level is almost empty.  I cannot be certain but it looks like there is a bit of petrol pulsing into the filter after the engine has stopped, suggesting that the petrol level in the carb chambers is reducing.  However, there are no obvious leaks.  Perhaps the carbs' heat is still drawing petrol in?

I guess that if there is no obvious reason for this happening, or any more tips, and the car still runs OK then I should either put up with it or remove the in line filter and not see the problem.

Regards

Mark

[Z320]

I like „not see the problem“

[Michel Higuet]

3 hours ago, MKTR said:

Many thanks to everyone who has contributed so far.  What I have done before/since is:

• have SU heat shields fitted
• replace the fuel pump diaphragm and valves with new ethanol resistant parts (just in case)
• re-routed the pump to carb fuel pipe in front of the water pump and wrapped with heat shield fabric
• changed all 8mm and 6mm rubber pipes
• replaced in line fuel filter
• checks all carb hose links and float valves
• changed my points condenser again

The good news is that I appear to have solved the drip under the rear carb and suspect the 6mm hose was cracked slightly.  Starting also seems slightly better when hot, but it is not like it is when the car is cold.

The bad news is that I cannot seem to keep a good level of petrol in the in line filter.  It is fine when just idling on the driveway, but when viewing after a good run out, the fuel level is almost empty.  I cannot be certain but it looks like there is a bit of petrol pulsing into the filter after the engine has stopped, suggesting that the petrol level in the carb chambers is reducing.  However, there are no obvious leaks.  Perhaps the carbs' heat is still drawing petrol in?

I guess that if there is no obvious reason for this happening, or any more tips, and the car still runs OK then I should either put up with it or remove the in line filter and not see the problem.

Regards

Mark

I send a pic of the filter on my TR4a...

 

When the motor is stopped the fuel line is still under pressure because in the mechanical pump there is a valve who doesn't allow the fuel to return.

"Perhaps the carbs' heat is still drawing petrol in?" to draw fuel through the jets you need a flow of air so a running motor.

"bit of petrol pulsing into the filter after the engine has stopped" in direction of the carbs I suppose.

I don't know but maybe ( a big maybe ) with a good run out your pump can cope with difficulty with the demand of fuel ( not the pump but his outlet valve ), the level is low in the float bowl and after the stop they still ask for fuel. ( when you open the line at the filter do you still have pressure? It must give a short giggle  ).

RobG already pointed to this "I assume the fuel pump button valves keep the fuel in the lines, so I suspect your valves are letting it drain back." I think the same

Easy to replace the two valves but in the right direction!

 

 

 

 

 

 

 

[RobH]

1 hour ago, Michel Higuet said:

When the motor is stopped the fuel line is still under pressure because in the mechanical pump there is a valve who doesn't allow the fuel to return.

This is not necessarily anything to do withe the non-return valves. . The mechanical pump works on a spring.  The cam and lever compresses the spring and it is the spring pressure on the diaphragm which does the pumping. When the engine stops, the spring is usually still compressed to some extent so still pumps fuel until the needle valve in the float chamber shuts off the flow.  The fuel in the pipe and your filter will still then be under pressure from the spring.  As fuel in the float chamber evaporates, the residual pressure will keep the chamber topped up until all the remaining spring travel has been used up. 

 

 

Edited September 14, 2023 by RobH

[MKTR]

Thanks Michael and Rob,

As indicated, I have replaced the button valves with the diaphragm so all should be OK.

At lunch I added an 8mm pipe non return valve just before the carbs, just to check if that made any difference and maybe indicate if it is the button valves.  However, there is no difference and I still lost fuel from the in-line filter.

Perhaps there is an issue with the fuel pump pressure, particularly when it is hot.  Is there anyway to check the outlet pressure, or is it a case of try a new internal spring?

I would like to ignore this but I also want to rule out anything that might fail soon.

Mark

[RobH]

Why do you expect the in-line filter to stay full?  Having it horizontal like that means there will always be an air bubble in the upper section as air will get back from the carb float chambers.  It will only stay full if you mount it vertically and at a lower level than the float chamber. 

[Z320]

The anti return valves are not 100% sealed and the petrol flows slowly back when the petrol tank is less than about 3/4 full

[MKTR]

12 minutes ago, Z320 said:

The anti return valves are not 100% sealed and the petrol flows slowly back when the petrol tank is less than about 3/4 full

 

29 minutes ago, RobH said:

Why do you expect the in-line filter to stay full?  Having it horizontal like that means there will always be an air bubble in the upper section as air will get back from the carb float chambers.  It will only stay full if you mount it vertically and at a lower level than the float chamber. 

Thanks again - I guess I presumed that if the carb chambers were full and the petrol pump had a non-return valve then there would always be fuel at the same level as initially primed to.  I did not realise that the valves leaked, so that is a good point to learn.

If I am worrying unneccesarily then I accept that and will try to ignore the levels or take out the filter.  Fingers crossed that nothing is actually wrong.

Regards,

Mark

[Z320]

Your worry is needless.

Sadly there are some mates out there making newbies worry about „air trapped“ anywhere

[Michel Higuet]

I can be wrong and it was long time ago but but if I reminder well, after changing the diaphragm I still didn't have fuel pressure, the outlet button valve was not working, open and the pump was not able to build a pressure in the system.

On my pic of the fuel filter after one week the fuel is still there at the outside of the filter. Seems no return to sender.

Sometimes you might think that there is some sort of voodoo magic around the TR but personally I still believe that the explanation is logical. :-)

 

 

[TR Micky]

Fuel vaporization has always been an issue with the four pot engine after a good heat soak.
My TR3a has had the problem badly this summer after standing in the heat, so I decided enough is enough I'm going to cure this problem.
1. Remove the old AC petrol pump and fit a blanking plate, make or they are readily available from Moss or Revington.
2.I fitted a small Facet pump (Up to 150BHP at around 1.5 to 2 psi.) as low on the bulkhead as possible via a small bracket with the pump ideally mounted on exhaust mounting bobbin close to the position of the old pump it will require a small amount of pipework made to suit, and remember to fit an inline suitable fuel filter. This pump is a pusher pump so it only required to push fuel to the carbs, as fuel is gravity fed to the pump from the tank.
3.Wire the pump, which only consumes about 2 amps via an ignition feed and fuse with a 5amp fuse (turn ignition on fuel is pumped to the carbs.)
4.This is only half the job done the final bit that makes it all work 100% is to fit a fuel return pipe back to the tank using 4.5mm rubber fuel pipe this size is ideal as it is a good push fit on to brake pipe which is ideal size to solder a piece of brake pipe into the filler neck, the flow rate can be controlled by a motorcycle tap fitted in the return pipe near the carbs this return requires just a trickle back into the tank. This arrangement also has the advantage of keeping the pressure off the needle valves cutting down on flooding issues and the tap can be turned off isolating the system during the winter months if required.  
5.Turn on ignition count to five; it is now picking up cold fuel hit the start button, instant start in hot conditions even after a hot engine soak.
I have had this system running for over six years with no problems and cure’s the embarrassment of starting a hot TR3a when you are surrounded by a crowd.
Try it, Total cost around £70.00.

 

[MKTR]

Just a quick update and to say thank you to everyone that contributed.

As noted earlier, I had marginal success with replacing most parts through to the carbs, and I even added some heat refelctive material to the pipework to help.  However, when checking the carb balancing I noticed an issue that might have been the problem all along.

With the air filters off and the engine just stopped, I noticed petrol flowing out of the top of the jets and dropping down into the inlet manaifold.  This I suspect was why my fuel level dropped in the in-line filter, and then why I had issues restarting later.

Although I had adjusted the SU float needles as per previous forum discussions, I had done this on the bench and had not done the additional step of seeing where petrol level was in the actual float chambers (when full) and their impact on the jets.  A couple of washers under the needle valves and all is well.  No drips, no fuel loss, and much better hot starting.

Mark

[Michel Higuet]

21 hours ago, MKTR said:

Just a quick update and to say thank you to everyone that contributed.

As noted earlier, I had marginal success with replacing most parts through to the carbs, and I even added some heat refelctive material to the pipework to help.  However, when checking the carb balancing I noticed an issue that might have been the problem all along.

With the air filters off and the engine just stopped, I noticed petrol flowing out of the top of the jets and dropping down into the inlet manaifold.  This I suspect was why my fuel level dropped in the in-line filter, and then why I had issues restarting later.

Although I had adjusted the SU float needles as per previous forum discussions, I had done this on the bench and had not done the additional step of seeing where petrol level was in the actual float chambers (when full) and their impact on the jets.  A couple of washers under the needle valves and all is well.  No drips, no fuel loss, and much better hot starting.

Mark

Yes a lot of people jump on the culprit the famous vapor lock, yes that exist but most of the time it is not the problem. There is no Voodoo Magic on a TR but yes sometime it is not easy to pinpoint the problem.