GT6 MK3 Fuel Vapourisation

[GT64fun]

John

Did Triumph not actually do this this as a later production modification, ie the heat spacer and pump with longer arm.

In other words the problem has always been there to a degree and I suspect Triumphs are not the only cars to be affected by this issue.

Regards

Ian

[John Bonnett]

Quoted from GT64fun

John

Did Triumph not actually do this this as a later production modification, ie the heat spacer and pump with longer arm.

In other words the problem has always been there to a degree and I suspect Triumphs are not the only cars to be affected by this issue.

Regards

Ian

It sounds like a good mod but i just wondered if the actuating lever on the pump is long enough to still be operated by the cam when the pump is stood off by half an inch or so.

[RobPearce]

The late Spitfires with the spacer would have been fitted with a different pump which had a longer lever. Unfortunately they're rather hard to obtain these days.

[Nick Jones]

Quoted from John Bonnett

I've just checked with Jerry and he assures me that he always uses 97 and 98 Octane fuel. The odd thing Nick is that i never had the problem on my GT6 which essentially is the same as Jerry's but without the side valances. I was interested in your theory about the temperature of the fuel pump but the inlet pipe although i didn't check it cannot be that hot surely? Perhaps the next step is to take off the valences and see if it still happens.

Thing to remember is that some components of modern petrol, (a right witches brew) start to boil at temperatures as low as 40ºC, further reduced at pressures below atmospheric (in pump suction line) and in areas of high velocity (pump valves).  The idea that really high temperatures are needed is wrong IMO, though certainly they make things worse.  Also, subtle things such as a slightly restrictive tank vent or in-line filter before the pump, that slightly reduce the pressure in the pump suction area could easily be enough to tip the balance.

Nick

[John Bonnett]

Quoted from Nick Jones

Thing to remember is that some components of modern petrol, (a right witches brew) start to boil at temperatures as low as 40ºC, further reduced at pressures below atmospheric (in pump suction line) and in areas of high velocity (pump valves).  The idea that really high temperatures are needed is wrong IMO, though certainly they make things worse.  Also, subtle things such as a slightly restrictive tank vent or in-line filter before the pump, that slightly reduce the pressure in the pump suction area could easily be enough to tip the balance.

Nick

Nick you really are a genius. Jerry's car is a slow filler which does indicate a problem with the tank breather. Perhaps as you say this could be a factor.

[markcro]

I spent some time on this last summer. I insulated the copper fuel lines from the fuel pump all the way to the carbs (I used rubber fuel line), I fitted carb heat shields and I exhaust wrapped the manifold and the entire down pipe back to the centre section. I also fitted an electric (Huco) fuel pump. It completely solved my hot start issues. I also note that it has drastically reduced under bonnet temperatures. (the gear stick used to get very warm on hot days but now it gets mildly warm)

Since I did all of this in one hit I can’t say which was the most effective. But I would guess the electric fuel pump would have a big part to play.

[timireson]

To prove it is the fuel I'm sure u can get "a system" that removes the ethanol obviously the cost per litre would go up but would be a good comparison.bim sure I read about it somewhere.
Tim.

[John Bonnett]

Thanks to your input I have a plan. Opinion seems to indicate that fuel boils in the pump. So I'm going to suggest to Jerry that we put a small motorcycle radiator fan in the side valance and blow cold air directly onto the pump. I can roll up a cylinder to duct the air where we want it. Hopefully this might solve the problem.

[markcro]

I have a clear filter fitted after the pump and it was always full of liquid petrol. On stopping the engine while hot the filter would quickly empty. Normally it wouldn’t empty. So that let me to believe that the fuel was boiling and creating back pressure to push the fuel back down out of the filter towards the fuel tank. So I would have said that boiling in the carbs was the big issue. Makes sense since the carbs are sitting over the exhaust manifold cooking like a frying pan.

[GT64fun]

Ok so project Huco has kicked off, with some stainless brackets fabricated to mount the Huco pump on the front side of the n/s suspension turret. I looked at other positions but this seemed the best option, particularly as my bulhead is aleardy full with a servo, electronic ign box and a T2000 washer bottle. I managed to fabricate a two part bracket (mocked in CAD initially), to pick up on the two engine mount to turret bolts and the front/top wishbone bolt. The pump should get a reasonable supply of fresh air in this position and is well away from the block.

The route from the fuel line to pump is quite easy and I will probaly add an in-line tap (because I already have one) and pre-pump filter, which will pass nicely over the top of the turret at about the level of the top of the side valance. The tap will allow me to shut the line off to change the fuel filter as with my current arrangement, if the tank is more than half full fuel flows out of the fuel lines when I disconnect the filter and I have had to jack the front of the car up before to deal with this (I dont like clamping fuel/brake lines).

So the next step is the routing for the pump to carbs. I'm keen to try and improve on the original 'round the head route' due to heat soak which looks difficult anyway from my pump position and round the back looks equally tricky.

Time for radical thought and I would appreciate comment on this. Triumph in their wisdom have provided some very nice holes in the main chassis members forward of the radiator, which seem to offer a route from one side of the engine bay to the other avoiding the hot bits. Using 7.6mm rubber fuel line (proper SA30 R9 stuff) there is a route forward from the pump, through the chassis rails in front the rad and up under the overflow bottle to the carbs. I may add a second in line filter at this point and use it to reduce from the 7.6 dia to the 5.6 diameter required for T piece between the carbs (already a bit non-standard here). The route is well away from heat sources and if I sleeve locally over the pipe, pretty safe in terms of chafe. The fuel line will fall slightly and then rise to carbs, but I dont tink this is a problem as there is rise and fall in the original system. A fwe photos attached.

Any comments or advice please.

Regards

Ian F

[Nick Jones]

Hi Ian,

I'd just worry a bit about what could happen in an accident....... 🤔

I would say run it around the back.  You can get insulating sleeving like this random selection https://www.heatshieldproducts.com/automotive/thermal-and-heat-shield-sleeving/thermaflect-sleeve.

My Vitesse injection system has the pump at the back and the pressure line run up the RHS of the car.  The gains made on that side are lost by the original line being used for the return.  The fuel gets warm (40 - 45ºC), to the extent that we have have problems with the tank overflowing just after filling as the fresh fuel picks up the heat and expands.

Nick

[Dannyb]

I agree with Nick about what could happen in an accident. I think this is why Triumph moved the fuel line round the bulkhead and not round the front of the engine.
Why not re-run the pipe from the tank along the right hand side of the car and then it just pops up on the correct side for the carbs, you can also put the pump in the boot.

[dusz]

I do not like the idea of the fuel pipe passing through the holes without suitable grommets. Vibration will cause the pipe to chaff aginst the unprotected edge and could result in a fuel leak.
I know it is more work but if you are fitting an electric fuel pump has anyone considered running the fuel line down the right hand side of the car so you do not have to root it around the engine? I have to add that I do not know the GT6 and don't know if it would put the fuel line closer to the exhaust.

[GT64fun]

Hi  All.

Thanks for the comments. Nick I did think about accident scenario. Perhaps the forward route is too risky although I think the chafe issue can be solved as the holed have nice rolled edges. Danny/Dusz the tank outlet is on the n/s, so rerouting to o/s of the chassis would be a fair bit of re-plumbing (support clips on chassis etc) and the exhaust downpipe is on that side in the engine bay, although as Nick says, he went this route with his injection.

Perhaps I'll try the round the back route first and see how it goes (I can then leave the existing pipe in place for the time being).

Regards

Ian F 🤔

[markcro]

My thoughts: I was going to re-route the fuel line to behind the block as suggested. But after thinking about this for a while, I reckon the line at the back will soak up just as much heat as it will do at the front. If you think of it, the air comes through the rad into the front of the engine bay, flows back past the engine block and then hits the bulk head. So the average temp under the bonnet must be relatively the same no matter where you are in the bay.
So in the end I left the fuel lines in their standard position around the front of the block but I insulated the entire run from the pump to the carbs. I just used rubber fuel line slit down the middle so that it fit snugly over the original copper lines and just cable tied it. It look neat as well.

I also had no space to fit the Huco pump on the bulk head, so I mounted it to the side of the engine block in the original position but with a heat shield added between it and the block.

This is just my thinking, I have no figures to back it up.


P.s. Wow! The white chassis above is spotless! I would be embarrassed to show the oily, filthy, tar like state of mine!

[Piero franchi]

if you read back on this topic, you will see I have a friends herald I am playing with, fitted with a spit 1500 engine, this herald and my own spitfire (used once for the le mans trip) are both doing prity much the same thing.

I took the friends herald out yesterday for a short trip, on the outward journey the carbs and there set up was standard, once normal temp had been reached the engine started to play up a little, holding back after a short stop at traffic lights etc, not running to bad on the straights.

on the return trip, I desided to do the same quick mod I did to my spit mk4,
I disconnected the breather from the rocker cover to the carbs, (you have to put a pipe from one carb to the other or they will suck in to much air)

and low and behold, A much happier running car, as said before, this is not the be all and end all, but it does remove some hot air going into the carbs.

one thing to note, my spit mk4 is running pancake filters, soon to be removed and reverted back to the original type filter box, with cold air coming from the front of the car via the filter box tubes.
my spitfire runs worse than this herald 1500. (my guess is these open type filters arnt helping by allowing very hot air into the carbs)

the herald 1500 has a standard filter box, with no tubs as yet (as we have not long acquired this car and not got round to fitting it yet)

I must say, I have noticed a lot of people complaining of fuel vaporization, are mostly breathing in hot air from there filters, BUT NOT ALL  

[RobPearce]

I drove Tessa down to visit Toby on Friday. She's been exhibiting hot fuel problems ever since the engine change, which I put down to the Herald fuel pump I fitted (because the original was for the early engine and doesn't fit the later block). On the way home she conked out completely after a stop at the Co-op, and wouldn't run again. Fortunately I was outside the local tyre centre who had a booster pack to let me play, but actually that wasn't really needed. I cadged a bottle of cold water, poured it over the carbs and pump, and bingo, she was running perfectly again.

So the problem isn't the routing of the fuel lines or the pancake filters (Tessa has the correct cold-air-fed filter box). It's heat in either the pump or the carbs. I'm going to fit an electric pump and see.

[john2502]

Interesting stuff and will be interested to see the findings you guys get.

I have never had any issues at all with the GT6 and fuel vapourisation and I've driven, stopped/re-started in hot weather and heaving traffic quite a fair amount over the last couple of summers of almost daily driving without this happening once.

Yes the cab gets quite toasty and the temp gauge does go up a bit but the car hasn't even stuttered. Running a standard fuel pump (which i think is the original or very close to the same age!) standard fuel line routing as well as standard carbs and airbox setup. Only difference being that it has aluminium radiator cowl/valences as opposed to the card ones (can't imagine this makes much of a difference)

I run on standard 95 unleaded from either Shell or BP and seems totally fine.

It used to happen sometimes on the mustang i had but that was cured with a phenolic spacer between the manifold and carb, quite a different setup though that

[RobPearce]

Yes, bizarrely my GT6 doesn't seem to suffer fuel vapourisation, or at least, not badly, despite being on the original setup with no spacers or heatshields. And Tessa didn't used to on the old engine.

[Kev W]

My GT6 is totally standard as well and in a great state of tune as I've had it on a rolling road but my blood runs cold when I see a traffic jam on a sunny day and I prepare to brake with the handbrake so I can keep the revs up in stop start queues! I am definitely suffering from vapour lock as when the traffic starts to move freely and I can get the revs up the coughing and spluttering soon stops! I've put a carbs heat shield on and even modded it to have a double skin but alas to no avail, I have a standard airbox also. I'm seriously considering an electric fuel pump! 🤔

[John Bonnett]

I'm pretty sure Nick has got it right with his theory that the problem is fuel boiling in the mechanical pump. This is borne out by a story i heard recently that when John Kipping was on a rally in Africa they suffered with vaporisation and pouring cold water over the pump got them going again. If this is the case, an electric pump mounted away from the heat should be an answer. In the case of Jerry's car, I think we are going to try to fit the fan to cool the pump. There isn't a lot of room so it won't be straightforward.

[RedRooster]

Insulated the stainless fuel pipes with HT sleeving, that's the last thing to try & I'm out of ideas then, not long before LMC traffic jams so will find out then if I've cured it.
RR

[John Bonnett]

Quoted from RedRooster

Insulated the stainless fuel pipes with HT sleeving, that's the last thing to try & I'm out of ideas then, not long before LMC traffic jams so will find out then if I've cured it.
RR

We've already done that Brad and still have the problem albeit less so. But you must have an electric pump so perhaps the sleeving will cure it for you.

[RedRooster]

Hi John,
Yes facet red top & filter king with a gauge.

Cheers
Brad

[John Bonnett]

The intention is to fit the fan on the valance and this should blow cold air onto the coil and the petrol pump. I have no idea whether it will work but I've enjoyed making up the assembly for Jerry.