GT6 MK3 Fuel Vapourisation

[John Bonnett]

Having lagged and insulated the petrol pipe from the pump to the front carburettor on Jerry's car I believed we'd put the problem behind us. But not so. Lining up in the queue for the ferry the engine cut out. Once it had cooled and the bowls refilled all was well. I never had this trouble on my GT6 and the only difference is that Jerry has side valances fitted and I didn't. I can only think that the divers side valance is holding the heat in the engine bay.

I'd be interested in what you think

[Piero franchi]

having had this on my spit mk4 and now on a new addition (a friends herald with a spit 1500) I have spent some time thinking about it.

nothing new in saying its defiantly modern fuel.

the question is what to do about it.

I for one am going to take a temp reading of the carbs, inlet and exhaust manifold, fuel pump and its pipes.

I dont suppose these will be out of spec as to how triumph intended, but simply to gauge any changes i make.

defiantly will be wrapping the exhaust, possibly might enlarge the water pipe that runs through the inlet manifold.

carb heat shields will do very little

a well maintained water system will help. but the problem is not heat,  so trying to lower the heat of the running engine will result in problems else were.

what i will aim to do is to cool were the fuel runs through

[Nick Jones]

Modern fuel with ethanol definitely more prone to vaporisation.  It's brewed for injected cars with high pressure fuel systems.

For total stoppage I suspect the vaporisation has to occur at or just before the pump.  The pump itself will be warmed by heat from the engine block with the lowest pressure in the fuel system, and thus the most likely spot for the fuel to turn to vapour, at the pump inlet.  The pump will not pump vapour well at all......  The situation is then made worse by the loss of fuel flow allowing the pump to heat up further.

Making sure that the pipe to the pump is run well away from heat source will help, as will using a pump with an insulating block between it and the engine.  Alternatively, using an electric pump located near the tank should help.

Most later carb fed cars had a recirculating loop with a return line to the tank from a restrictor just after the carb(s).  Purpose of this was to ensure that the pump always pumped at full rate regardless of the demand from the engine, with the flow of fuel keeping the pump and lines cooler.  This does eventually heat the fuel in the tank but hopefully you are not stuck in traffic long enough for that to be a problem.

Nick

[bob dunn]

https://scontent-lhr3-1.xx.fbc.....b044&oe=57CFA62B

[bob dunn]

How about a Le Mans vent.

[Nick Jones]

Quoted from Spitfire6

Hi,
If you think Ethanol or vaporisation is a problem; try higher octane fuel that is less volatile and contains no ethanol.
As read on internet.
Busy looking for link.

Cheers,
Iain.

Don't think it's solely down to the ethanol content (though it certainly doesn't help) and not sure that many of the high octane fuels are ethanol free these days either?

Nick

[efp]

Would something like this help you find the point in the circuit that has the highest temperature?

http://www.maplin.co.uk/p/infr.....gUnrSd8WDRoCLAjw_wcB

[JohnD]

Quoted from Piero franchi

defiantly will be wrapping the exhaust, possibly might enlarge the water pipe that runs through the inlet manifold.

carb heat shields will do very little

Piero,

Please search around, here and on other sites, for the many discussions of exhaust wrap.    There was a thread recently in which someone had actually done some measurements of the effect of wrap. It was significant but tiny.   Damned if I can find it though, sorry!   And the wrap does weird things to the metal of the manifold and down tube, or primaries if you have a tubular manifold.   I think it goes hypoxic, the metal gets blued and the metal flakes away.

And heat shields DO work!   The exhaust heats the carbs by radiation.  Put a metal sheet in the way, and it will absorb the heat.   It will get hot in doing so, but because it has a much larger area than the exhaust or carb not very much.    The heat it will re-radiate towards the carb will be from a much cooler body, so the carbs will heat up less.

Lastly, almost all the heat under the bonnet comes from the radiator, not the exhaust or the engine block.   I built my race Vitesse Silverback with a rear radiator, and it was a cold car to drive!   No heat unbder the bonnet, no heat inside the car (no heater, either!)
John

[nang]

Most later carb fed cars had a recirculating loop with a return line to the tank from a restrictor just after the carb(s).  Purpose of this was to ensure that the pump always pumped at full rate regardless of the demand from the engine, with the flow of fuel keeping the pump and lines cooler.  This does eventually heat the fuel in the tank but hopefully you are not stuck in traffic long enough for that to be a problem.

Nick
[/quote]

Just about to suggest this but you beat me to it.
My Mk 5 Cortina had something similar as do diesels
Tony.

[Piero franchi]

Like I said, I had NO END of trouble with a spit mk4 that I bought a couple of years back with its sole purpose of being used to take me to La Mans

I have read a lot of talk on this subject, but have not heard of any data.

so its my intention on investing in a lazer thermometer and seeing whats going on.

I am of a different opinion, and ill explain,

first off, with regards to My Spit mk4, this car had no engine valances, no carb heat shields either,

it would be run from cold out side my workshop with the bonnet up, after a while, she would get fuel boul flooding.

SO one thing I can conclude, is in MY case at least, it was not a problem caused by heat from the cooling system.

(I think I posted my problems either hear on club triumph or the sideways forum),

I fitted a fuel regulator as many people blamed the fuel pump for over pressurized the carbs, the car run a tad smoother bit it did not stop my problem,

so one thing I can say its not from the pump to the carbs, as I fitted my fuel reg close to the carbs, and ran a new fuel line away from any heat straight to the carbs.

I cant say this enough, I believe the cause is the fuel, the solution is the challenge.

you defiantly dont want to change the core temp of the engine, the challenge is to cool were the modern fuel runs through.

I make bio diesel and that has given me a in site to the challenges of changing fuel's,

with the GT6 and spit, we have a exhaust and inlet manifold right next to each other, the radiant heat is massive, the radiant heat from the head to the inlet manifold is huge as well,

(remember with my spit mk4, it was sitting idle and it still had problems)


if any one did remember my La mans trip and the car prep issues, you will remember on the night before I left, at around 10 or 11 pm, I stopped listening to all I had read, tried to de stress and work out what was going on,

what I did was to disconnect the hose from the rocker cover to the carbs, I had to block each end of the hose but the car ran a whole lot better. I believed at the time, this could have been adding pressure to the carbs, and adding the fuel boul flooding

IT DID NOT cure the problem mind although it did make it possible to make the trip, both ways on its own steam, with the backing sun on Saturday, I was forced to do a pit stop and fab a pair of heat shields from some thick alloy sheet at the side of the road for the carbs, this to did NOT resolve the problem.

now going back,
with a car thats sitting idle, bonnet up, fuel reg fitted, no engine valances, Whats the problem??????     fuel

one thing to note, I think the use of pan type air filters is a massive no no if you have this problem, mine had them fitted, my friends new herald 1500 has original box type

I believe there is a lot to be had from re fitting the original air box and making sure you are getting fresh cold ish air into the air system,

there is cooling to be had from this air.

thats s why in my instants, my inlet manifold was always hotter than the carbs,

I tig weld, and believe you me, alloy will sap any heat from were ever it can get it, them carbs will soon be as hot as the heat source,

the colder charge of air is with out a doubt cooling the carbs to a degree

we need to re think the whole system,

one thing I will bet you, if I was to run fuel of yesteryear I would not have these issues

[JohnD]

Piero,
Lets look at the symptoms to reach a diagnosis.

"My Spit mk4, this car had no engine valances, no carb heat shields either,  it would be run from cold out side my workshop with the bonnet up, after a while, she would get fuel boul flooding."

You correctly (IMHO) found this was because under conditions of least fuel use, the pump pressure was overpowering the float valves in the fuel bowls.

BUT, " I ... disconnect[ed] the hose from the rocker cover to the carbs, I had to block each end of the hose but the car ran a whole lot better. I believed at the time, this could have been adding pressure to the carbs, and adding the fuel boul flooding."
Difficult to see how that could contribute.  Was there a high crankcase pressure, and a lot of blow by into the inlets?   You say, "IT DID NOT cure the problem"

And flooding is the opposite of fuel starvation due to vaporisation.


You make your own biofuel?  Wow! Respect!  Can you change the recipe, to alter it's vapour pressure?  I understand that 'petrol' is a mixture of compounds with different VPs, but they do interact.
John

[Piero franchi]

and what happens to something when it vaporizes????

I would say it expands first,

it would be easy to believe that the fuel bouls were simply flooding due to to much fuel and not flooding because of to much pressure casuesd by the expanding vaporizing fuel

[Piero franchi]

dont forget, I fitted a fuel regulator as close to the carbs as possible

[Piero franchi]

if memory serves, I do believe I run a short fuel line from a Jerry can straight to the manual fuel pump to eliminate a air leak

[Piero franchi]

You correctly (IMHO) found this was because under conditions of least fuel use, the pump pressure was overpowering the float valves in the fuel bowls.

I never said this or found this to be the case!!!!

[John Bonnett]

Quoted from Nick Jones

Don't think it's solely down to the ethanol content (though it certainly doesn't help) and not sure that many of the high octane fuels are ethanol free these days either?

Nick

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.

[RedRooster]

Had a bit of grief with this as well, usually on hot summer days in traffic.

I had the problem with Strombergs & a mechanical fuel pump as well as triples & an electric one.

To date, heat shields under the carbs, stood the coil off & heat shield, changed to Stainless fuel pipe in the engine bay, took the rear bonnet seal strip off & replaced with small sections to get some air out, also aux cooling fans in the valance to bring cool air in, electric fan on manual switch as could never get the hysteresis right on the capillary.

Last thing to fit before Le Mans is sleeving over the fuel pipes.

It's definitely vaporization as with all the fans on it behaves itself but i'd rather not drive around sounding like a Dyson.

RR

[Piero franchi]

having just done a resent google search on the matter,  you come across lots of classic car owners all the with same type of problems, all have slightly different set of serconstances but the underline issue is the same.

different makes and different models, we with are triumphs are no different,

some get away with it as there set up is slightly different, maybe they have a straight through head, maybe they have a very large grill with good air flow,
all this is not the point,

the point is, there is a lot of trouble now that was not around in years gone by, this was never a problem,

in years gone by, when there was a similar problem, YES we could look at it in the way most people are trying to diagnose it today,  only things have changed, and that is our fuel.

like I said, what can you do about it!!!!!!!

I dont want to rely on a car that can only run a high octain fuel.

I know when driving abroad, late at night, you sometimes dont have a choice were you fill up or with what

I will try this !!!!!!!!1

I am going to run my friends herald 1500, I will bring with me, some thing or a way of cooling the intake manifold, maybe water in a bottle who knows,

I will drive it till is starts miss behaving and then will stop, I will keep the engine running and I will attempt to cool the intake ONLY,  no fuel lines or fuel pump.

I will report back honestly even if its not what I think its going to be, no point in missleading people

[RedRooster]

Can you take a video when you do that

[Piero franchi]

dont panic, its not like I dont understand the problems with cold water on or near a hot exahust 😉

[GT64fun]

This a problem that I have had with my Mk2 GT6 on a couple of occasions over the last year (luckily idling at home on the drive after a run) but experienced much more seriously last weekend when driving to and from an MOT test. The car has the standard (original & rebuilt) fuel pump, coil spaced off, standard radiator, engine bay valences and radiator shroud, an electric SPAL sucker fan on a Revotec controller, standard fuel pipe routing in copper, carb heat shields and K&N filters. (Oh and Shell V Power usually)

To be fair it was a warm day 20 deg C and the car was getting a bit hot, as I seemed to hit traffic which ever way I tried and when vapourisation  occurred the engine just cut and I had to limp off to a relatively safe position (on the starter) to try and resolve it. Luckily I had my basic tool kit. The filter immediately upstream of the pump was empty (seen that before) and taking the top off the fuel pump there was a hiss of pressure and showed the fuel merrily fizzing away in the bottom of the chamber. I broke the fuel line just upstream of the carbs and having reassembled the pump, managed to hand prime so that fuel flowed through the pipe. I then reconnected it to the carbs and it immediately restarted. It happened a further 3 times before I finally got home. Oh the joy of classic cars.

The carb heat shields have definitely reduced the running temperature of the car bodies, but my feeling is that the problem really is the mechanical fuel pump in contact with the hot block as that is where I can actually see the fuel boiling. The routing of the fuel pipe around the front of the head may be an contributory factor (this has been discussed previously) but presumably Triumph did this to expose it to fresh air entering the engine bay. Long term I have a number of ideas including an upgrade of the radiator, but initially and with Silverstone Classic (and then the RBRR) looming, I am thinking about fitting a Huco suction pump on a bracket fixed to the rear of the nearside suspension turret (ie off the block). Stainless shielded fuel pipe is also another relatively easy option and I am tempted to revert back to the mechanical plastic fan as the engine heat does seem to cycle a bit with the electric fan and if it is set too low the fan is coming on early and staying on late, almost as if it is fighting the thermostat.

I will update as to the effect of the pump change, but any comments welcome and I will  follow the rest of the thread with interest.

regards

Ian F 😲

[John Bonnett]

This does rather confirm Nick's theory that the problem is petrol boiling in the fuel pump. In Jerry's case the problem is nothing to do with coolant temperature; it has always been on Normal. So the question is, can the fuel pump be stood off from the block with an insulator fitted and still operate mechanically?

[Piero franchi]

like I said, different people have slightly different issues, but all have the same underline problem.

Its interesting in yr case you saw the fuel boiling at the pump, a solution for YOU may well be to go electric

I on the other hand when fitting my fuel regulator purposely fitted a temp clear hose so I could keep a eye on fuel or lack of it.

its funny who the likes of Kenlow made a lot of money back in the day when they were first changing our fuels

[RedRooster]

I sleeved the thermostat as well, but had the same problems before & after.

[Piero franchi]

O and before I head off out, read this, be it with a pinch of salt.

http://www.carbkitsource.com/carbs/tech/articles/TuneUp/CarburetorTuneUp08.html

this is NOT a fuel pump getting hot problem like some of you hear, BUT its still a modern fuel problem.

like I said in the start, we need to know whats going on with OUR particular car, as the modern fuel affects different cars in different ways