Difficuilt to start gt6 engine when hot

[Alfie]

Been trying various fixes to get my Mk3 gt6 engine to start easier when hot, at the minute i have to floor the throttle with a little choke and keep cranking till it fires up this can take 10 to 20 seconds which i think is to long. The carbs have been fully overhauled, engine has new rings with honed bores with hardened valve seats for unleaded. Also fitted new dizzy arm from dizzy doctor online in case it was faulty when hot as ive read there was a batch of dud ones. Electronic dizzy fitted from H&H.

When the engine is cold it start first turn on the choke so my thought is its running lean plus the possibility of fuel vaporization, this i have tried to overcome by insulating the copper fuel pipe around the carbs plus Ive fitted a stainless heat shield and wrapped the exhaust manifold and exhaust system in heat wrap to cut down on heat radiation, once the engine does fire up the choke is pushed home and it ticks over happily, the exhaust fumes smells rich to me which contradicts the lean theory so i am now at a loss as to what to do next. The engine pops when on throttle over run which indicates its running lean, i adjusted the jets to enrich which took the popping away on throttle over run but still had the hot start issue.
This problem occurs even if the engine is stopped for 5 mins for say a refuel at a petrol station, just the other day i had to push the car away from the pumps and lift the bonnet to cool the engine down for 10 mins at which point the engine started.

Any advice welcome, and just in case it helps ive fitted a fuel regulator and gauge then tried various fuel pressures from 2 psi to 8 psi which makes no difference to the hot starting problem.

[JohnD]

How is your fuel supply to the carbs routed around the engine, and do you have heat shields to protect them from the exhaust manifold?
I'm thinking fuel vaporisation due to excess heat.

JOhn

[Alfie]

The fuel line has been re routed along the bulk head in rubber pipe clipped to the bulk head and any copper lines have been covered in a heat reflective sleeve. There is a stainless heat shield behind the carbs between the carbs and exhaust manifold.

The one area that has direct contact with the block is the mechanical fuel pump, ive changed this (metal top not a glass bowl top) to eliminate it but now are starting to think an electric fuel pump may be the way to go. Ive read the electric fuel pump was chosen when fuel vaporization caused the engine to cut out in hot weather not poor hot starting so still not convinced the elec pump is the way to go.

I seem to be making more questions than answers so far.

The dash pot oil is general engine oil, why do you ask

Any advice guys from some body who has manged to cure a poor hot starting Gt6 engine.

[Royboy66]

Hello Alfie ,

Has the issue started since you changed the pump ?  

Some 'new'  metal top mechanical pumps are not great !

Just. Thought

Roy .  

[junkuser]

Pump pressure too high certainly can force fuel past a needle valve that behaves itself when engine is running, but it seems that you have covered this point.

Warm engines require a leaner mixture than cold ones, so become rather sensitive to richer mixtures, particularly when starting, which you also appear to be aware of.

"at the minute i have to floor the throttle with a little choke" is leaning off the mixture, as wide open throttle simply lets in air on a constant depression type carburetor with no accelerator pump and a little "choke" would cam the throttle rest position up with little or no pulling down of the jet, which is your logic behind using this method.

Have you tried just leaning the mixtures a tad by adjusting jet level?

I still suspect a needle valve sealing problem causing an elevated fuel level resulting in a richer mixture that a cool engine can tolerate but not a hot one.

[JohnD]

The original fuel hose/pipe route was around the front of the engine, perhaps so that Triumph could avoid the expense of heat protective coverings.

A way of testing the overheat hypothesis would be to simulate a ten/ fifteen minute run (if that would cause the restarting problem) with the bonnet up.   If there is no problem restarting then, you need to look at  fuel vaporisation rather than anything else.

John

[glang]

This problem is very common in the triumph sixes and I dont think the fuel line causes it as its the fuel in the carb bowls that is used for the starting and running afterwards for quite a while on tickover. I suppose it could be vaporisation in the bowls but where does all that fuel vapour go? This could be tested by refilling the bowls with the manual fuel pump lever (if your model has one) before doing a hot restart to see if theres any improvement.
However if the compression, timing and carb adjustments are all ok I suspect its down to the high temp in the engine/engine bay affecting the combustion process so on my vitesse Im working on reducing it as much as possible. This means a monster electric cooling fan that will run on without the ignition, exhaust manifold wrap and if possible additional air venting (ideally in the top of the bonnet but this would be the last step).  

[don cook1]

Maybe its the condenser, these break down when hot and cause your problem.

[Alfie]

Thanks for all the replies guys.

Ive fitted electronic ignition and replaced the rotor arm with one from the Dizzy doctor online.

Today i took the car for a good hours drive parked up for 10 mins with the bonnet closed then tried to start the engine with no joy, even after trying the full throttle scenario. Lifted the bonnet to check the glass filter bowl on the King fuel regulator/filter and surprise surprise the bowl was totally empty tried to manually pump fuel with the lever on the mechanical pump but no resistance in the lever so cranked the engine over still no fuel being supplied to the glass bowl so slackened one of the fuel rubber hose clip's on the front carb and slid the rubber fuel pipe off the copper pipe at which point a pressure hiss could be heard with a strong smell of petrol, replaced the rubber pipe , cranked the engine and the glass bowl started to fill with fuel then the engine started.
There is never a fuel issue when the engine is running, no starvation under heavy throttle or poor tick over how ever if the engine is ticking over for a number of minutes at stand still and the twin electric cooling fans kick in the revs drop due to alternator load then after a few minutes the engine stalls, lifting the bonnet shows no fuel in the King regulator glass bowl.

This all points to fuel vaporization which must be creating an air lock in the fuel supply pipe that the manually pump can not overcome so fuel starvation occurs. What i need to find out is the air lock in the new mechanical pump which would indicate the no resistance in the pump manually lever i felt when i tried to manually prime the system or is it in the pipe from the mechanical pump to the carbs either way it points to heat build up in the fuel pump transmitted from the engine block plus the hot air being blown over the engine bay by the electric cooling fans.

If this is the case how can i overcome this, would fitting an electric fuel pump be the answer and also why would triumph design a fuel system that was unreliable to say the least OR is it modern fuels that have made the problem worse.    

[JohnD]

No pressure should build up in the carburettor float chamber.  There is a vent tio lete ai/gas/vapour out.

If you have SUs see: http://sucarb.co.uk/technical-carburetter-maintenance-settings-flooding
If Stromberg see: https://www.triumphwedgeowners.....anual_-_complete.pdf

JOhn

[Alfie]

With what you have said JohnD regards no pressure build up in float chambers, i need to re create the hot start issue then drop the carb fuel bowls to see if there is fuel in the float chambers which should be the case if the float needle valve is closed so causing the build up of fuel vapor pressure in the carb fuel supply pipe.

[Jonny-Jimbo]

Reading what you said at the start my guess would have been fuel vapourisation in the hot engine bay. Used to happen on the Lotus Elan, so when stopping or filling up, Dad had to pop the bonnet to allow the hot air out and this prevented the vapour lock.

[RedRooster]

Getting the hot air out from the engine bay helps, have you the long bulkhead to bonnet seal fitted? If so try smaller sections.
On my car I also have aux fans in the valances bringing colder air in, 75mm IP56 rated.

RR

[GT6 M]

On my car I also have aux fans in the valances bringing colder air in, 75mm IP56 rated.

RR[/quote]

Would it be no better to them sucking the air  oot!!

As for the rubber bulk head strip,

I did this yonks ago, and with fan on, the fan shifts the air thru this bigger gap,
moer hot air gets out, then moer cold air can get in, simples.


Rooster, try this for yer Avatar,

http://www.therevcounter.co.uk/filedata/customavatars/avatar603_2.gif

M

[Alfie]

I am wondering if maybe there is a pipe in the wrong place or missing, has anybody got a photo of there MK3 GT6 engine carburetor side so i can compare.

[RedRooster]

Quoted from GT6 M

Would it be no better to them sucking the air  oot

Probably, but I mounted them at the front of the engine valance, so there they are best pushing.
Still got to sleeve the fuel pipes before the run to Le Mans Classic, the traffic jams there are a good test if I have cured the problem.
RR

[Alfie]

The SU electronic fuel pump has arrived, fitted beside the fuel tank in cool air. Ran the engine until upto operating temp then swithched off for 5 mins and trued to start again but no luck had to lift the bonnet and leave for 15 mins to cool down, the engine then started after a littl cranking over.

So my thought is to pull the carbs off and check over the float height and also the fixed jet height in relation to the carb body, both carbs were overhauled so there may be something i have missed or set incorrectly when overhauling them.

Does any body know what the measurement is between the top of the fixed jet and carb bridge?  

[nang]

Not having this problem with the Spitfire but have run a rubber pipe around the back of the motor. Do your carbs have Waxstats fitted? If working these will weaken the mixture. Although, saying this your description does sound like evaporation.
Tony.

[Alfie]

Don't have the waxstats fitted. One of the many things Ive done was to run the fuel line around the rear of the block on top of the bulkhead which made no difference so next move will be to strip the carbs and check them over.

Any body have the correct the height the fixed jet is below the carb body bridge.

[Jonny-Jimbo]

I would have thought that round the back of the block would have more stagnant hot air than round the front of the bock, where although there is hot air, it is at least mainly moving.

[efp]

That's something that has puzzled me: early spits seem to have had the fuel pipe from the pump to the carbs routed around the sharp end of the engine, as it were, over the thermostat housing.  But mine, and most others I've seen, have it routed at the bulkhead end now.

Maybe a red herring but I agree, it does seem logical that the front end would be a bit cooler, albeit not much,  and as the pipe run is longer I'm wondering if Triumph didn't originally do it that way for a reason.  Though Thomason does suggest that the aft routing from FH50001 on the Mk4 was to reduce heat pick-up in the pipe.

Can't think it makes a huge difference, but intrigued. Someone with more patience than me and having one of those infra-red thermometer jobbies , might like to investigate one day

[drofgum]

Hi,
I think the re-routing of the fuel line was related to crash safety. The back of the engine being less exposed.
As far as temperature goes, routing the line between the water pump and the thermostat housing doesn't strike me as a cool route for the line.
                                                                                         Regards,
                                                                                         Paul

[efp]

Not sure I can agree Paul.  Surely the he main source of heat has to be the exhaust manifold which as discussed  elsewhere here, gets ludicrously hot, while the water system  gets to maybe 120 max internally?  Makes sense to me to route the pipe in the cooler air flow at the front.

But as always, I defer to those with more knowledge than me.

Best
John

[RobPearce]

Also, bear in mind (at some risk of being shouted down like I was in the Courier many years back), the fuel that's passing (fairly quickly) in front of the engine has just come from a pump that's bolted to the block. I know my old Mk1 Vitesse used to fill the glass bowl with vapour when it was warm.

[Martins Stag]

So to add my two pennys worth I have my fuel pipe routed round the front of the block in rubber pipe and it seems to be ok. It is a 2.5 litre. I do have a Facet fuel pump mounted by the battery and I have got rid of the mechanical pump as it couldn't pump enough pressure under load! Not sure if this helps or hinders.
Martin