GT6 MK3 Fuel Vapourisation

[markcro]

Nice clean car! Very clean!

[John Bonnett]

Quoted from RedRooster

Bastard car.

Surely it hasn't packed up already?

[RedRooster]

Yes 3 times so a 2_1/2 hr jouney took 6_1/2.
In the end i proped open the bonnet to get some airflow which helped but didn't cure it.
Took some temp readings, gauge at 75, carbs 40, Inlets 77,.dizzy 49, coil 49, spare coil 47, cant remember the fuel lines but they were not excessive.

[John Bonnett]

Quoted from RedRooster

Yes 3 times so a 2_1/2 hr jouney took 6_1/2.
In the end i proped open the bonnet to get some airflow which helped but didn't cure it.
Took some temp readings, gauge at 75, carbs 40, Inlets 77,.dizzy 49, coil 49, spare coil 47, cant remember the fuel lines but they were not excessive.

Some impressive temperatures. Did it cut out when you were driving or just when you were stationary or in slow moving traffic?

[RedRooster]

Every time at a junction or roundabout in traffic.

[GT6 M]

Ahaaa, yer on Webbers or Dell,ortos,
I tek it that the rubber O ring is still free,ish between carb an mani.!!!

if its tight, nee flex,  it,ll give the symtoms ye experiancing.

M

[markcro]

Just something to check: as part of my months of search and heat shielding, I found that the voltage to my coil was varying with temp. Some days perfect, other days the voltage dropped way too low and that is when what I thought was vapourising was the issue. So check the voltage to the coil, or test with a cable directly from the batt to the coil. In the end I ran a new circuit directly to the coil.

[Nick Jones]

I also am inclined to wonder about ignition issues.  I'd suggest "hot-wiring" the coil feed directly to the battery next time you have an issue and see if that makes any difference.

I also note your Malpassi Filter King regulator. These are good kit but it is well placed to pick up alot of heat so I also be tempted to pour a bottle of cool water over it next time you have an issue (after trying the hot-wiring)

Nick

[RedRooster]

I think i have some wire in the boot to run another feed to the battery.

The dellortos have the cup washers fitted to the inlets so they are at the correct tightness.

Good point about the filter king i will try that.

Spoke with some locals last night they said there car was reading between  33 to 37 ambient temperature yesterday! The forecast was for 30.

[RedRooster]

It did it again in the mega Le Mans traffic jams.
Hot wire from the battery no differance, spare coil no differance, bottle of water over the filter king no differance, it took an hour to cool down this time, the only good thing about it was we saw most of the cars drive by to the club parking so didn't need to walk around the circuit so much.

[GT64fun]

Huco now fitted, plumbed and wired. I have added an inline tap where the flexi fuel pipe comes into the engine bay, so I can change the filter without having to jack the car up when the tank is reasonably full. It is an easy short level run from the filter to pump. I have routed the pump to carbs line around the back of the bulkhead and managed to thread the pipe round the back of the washer bottle, header tank servo etc. The pipe is very thick walled but surprisingly flexible. I dont think there are any potential chafe issues here but I will monitor.

I ran about half a pint of fuel through the system before connecting up to the carbs. It fired up easily and on restarts after a short stand, there are a couple of pulses from the pump as it tops up the carbs. I let everything get nice and hot (fan cycling on and off a few times) and then went for a run.

First impressions are good. Pump and lines are warm, but much cooler than the mechancal fuel pump and the original copper pipe next to the head, which are almost too hot to touch.

Siverstone Classic in a couple of weeks, so bigger tests to come!, but so far so good.

A couple of photos attached.

Regards

Ian F 😉

[RedRooster]

Back home again safe n sound, bit cooler today with some light cloud cover, so bit of a love hate drive back.

Sunday quiet back roads, long undulating & fast, up on cam (new roller rockers working well too), full throltle VvvrrooommMM off we go, 6 cylinder on song, this is what the car was made for, I love my GT6.

Into a town, elderly / hungover drivers dwaldering about, oh no the temperatures going up, stay alive you b@stard, I hate my GT6.

Clear the town VrrooommmM were off, I love my GT6, repeat for endless villages & a few hours....

RR

[John Bonnett]

It may not be the definitive answer but Jerry's car never missed a beat in the stop start traffic leaving Powderham yesterday and it was a hot day. So result looks promising.

[John Bonnett]

The fan blowing cold air directly onto the fuel pump appears to have solved the problem on Jerry's car. It had quite a severe test over the Silverstone weelend a and never once gave any trouble.

[GT6 M]

this something I wastrying to tell a Capri X Pacowner on Sun

he said his car starts hunting when in town  / traffic.
its not cutting oot as such, butt, runs quite bad he said.

reason, the  air temps going up,
ye aint got nee facility to alter the ign, nor the fuel delivery amounts

as the air gets hotter, it gets thinner,
butt, the fuel sucked in, still remains the same
so yer engine gets moer fuel than needed., so runs rich


then, after fuel has got hot too, ye will most likely be suffering frae vapourisation probs too,
so then, engine goes frae being too rich, to getting nee fuel at all,
hence the eventual conkin oot.

Any one wid a ECU fited, wid a ex sensor reading will tell ye, { if they actually have took notice of this,  tink Nick will be onto this.}
that the ECU will decrease fuel amount as temp gets higher, and also it retards ign too.

mine does, and can tek 15-20 exta fuel oot at idle
butt, wen engine is cold,or, moer specific, no much heat coming oft ex to heat the inlet manis, then ECU actually  Adds fuel, upto 10-14%
which slowly goes doon as temp raise, till its detracting fuel.

this can be reduced by switching engine fan on, and it drops to 12-15 %
as moer hot air is being shifted thru me vents.

Me self, after all the mods ye done / tied, this seems tobe logikal culprit
as modern fuel boils alott sooner than olde fuel frae pre Ethanol times.

Can try running it on 100LL avgas,
as this is designed to not gas off as much, nor change as much in its structure.

can also try running yer fuel thru a external cooler, befoer it gets to carbs
and also  try running wid yer fan on { if electric } and having the bonnet propped open by say, a couple of bogg rolls
see if this extra opening, letting hot air oot will help
{ the vents in me bonnet worked  to get rid of fuel vapourising when I ran PI., along wid other mods }

M

[John Bonnett]

I think most of us believe that the problem is a result of high under bonnet temperature which is probably more from the radiator than the exhaust manifold.

My suggestion to lower the under bonnet temperature is to fit a 72 degree thermostat. A Triumph engine builder ran some tests and found a higher power output when running a cooler thermostat so the only downside would be a less efficient heater..

[RedRooster]

Is there any mileage in plumbing in a return to tank line at the filter king input so that some fuel is circulating which would keep the temperature down?
RR

[John Bonnett]

Quoted from RedRooster

Is there any mileage in plumbing in a return to tank line at the filter king input so that some fuel is circulating which would keep the temperature down?
RR

Would you not T it in at the end of the line by the last carburetor?

[RedRooster]

I suppose you could, just didn't want to rob the carbs of fuel.
Will need a one way valve inline back to the tank i guess as well.

[glang]

Sounds sensible to me John then with a regulating valve to ensure that the recirculating flow leaves enough pressure to supply the max demand of the carbs....

[RedRooster]

I have a spare fuel tank filler hose with a vent line from the Beam, was thinking i could use that for the return.

[GT64fun]

Following up on earlier comments re breathers and possible contributory factor to vapourisation, I went searching for mine on the Mk2 GT6.

Being unable to find it I checked my w/s manual and Canley's website.

It appears that the Mk2 doesn't have one, presumably relying on the small hole in the filler cap. Canley's parts diagrams show one for the Mk1 but not the Mk2. The red workshop manual (issue 2 for this section) says no breather on the Mk3 (implying present on the Mk1 and 2) so not quite correct.

Regards

Ian F 😉

[RedRooster]

Been thinking about this & doing some research.
My Red top has a max flow of 35 gal/hr (2.2l/min) & a 2litre engine needs 0.68 l/min at 6000rpm, so plenty of reserve in the pump.

The more i read about recirculating the fuel the less i see a downside about it, so rather than do a gash test job i might as well do it properly. I can use a double fuel banjo on the last side choke, then reduce this down to 3/16 (brake pipe 7 times less area than the fuel feed) route the pipe across the bulkhead, clip it to the chassis and run brake line back to the filler neck on the fuel tank.

Anyone any comments?
Brad

[glang]

will you include a valve in the return to allow some adjustability or rely on the calculations? It certainly sounds like you've got plenty of spare capacity with your pump....

[RedRooster]

Quoted from John Bonnett

My suggestion to lower the under bonnet temperature is to fit a 72 degree thermostat.  

Haven't used a thermostat for over 2 decades, use those drilled out blanking sleeves after having a thermostat seize on me.
RR