Difficult start - only when heat soaked E-Type

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jagwit
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Location: Pretoria
South Africa

#1 Difficult start - only when heat soaked E-Type

Post by jagwit » Wed Mar 29, 2017 10:54 am

My V12 starts on the first crank when cold - using choke, no throttle application required.

Its starts equally well when hot - if being restarted within, say, 5min of being switched off with about 25% throttle.

Trouble is when it has stood hot for say 20min or longer. Then it will crank for an embarrassing amount of time before lazily coming to life. No amount of throttle seems to help. I also wait until I can hear the fuel pump has filled all the carb fuel bowls.

Any ideas why this is?
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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jagwit
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South Africa

#2 Re: Difficult start - only when heat soaked E-Type

Post by jagwit » Thu Mar 30, 2017 8:02 am

With the aid of input received from Jag-lovers, I believe I have solved this issue. (Will test the car later today)

Before I continue, I should add two (relevant) symptoms worth mentioning:
- when starting the car, I always allowed the fuel pump to "settle down". This meant the clicking of the fuel pump came to an almost complete stop, clicking only once every 2-3 seconds. This is an important clue that confirms that fuel was not FLOWING to the engine and back to the tank!!
- When it did start eventually (being heat soaked), there were no clouds of black smoke indicating 1) that the engine was NOT flooded and 2) by virtue of not starting, there was inadequate fuel levels in the carbs.

There is a non-return valve in the fuel line (see picture - right click and select "view image" for a good look).
tn_20170330_085828.jpg
tn_20170330_085828.jpg (103.72 KiB) Viewed 1911 times
Whilst it may prevent fuel from draining back the way it came, I believe its purpose is two-fold:
1) to allow continuous fuel flow from the tank to the engine and back to the tank (to purge the system of vapour during heat soak conditions);
2) to still create sufficient pressure to the float bowls for fuel to enter the carbs as needed.

The NRV on my car had one or two problems:
1) either it was stuck (because this car has stood for many months at a time, its possible that fuel evaporated leaving the residue to effectively "glue" the check ball to the housing); OR
2) the spring in the NRV was too firm such that pressure generated by the fuel pump could not overcome the force needed to open it. (It could also be that the original fuel pump in my car does not generate sufficient pressure - which I doubt)

SOLUTION:
1) Opened the valve to free the ball bearing (it was very clean otherwise);
2) I inserted more copper washers between the two halves to reduce the spring pressure on the ball bearing so that it would open easier. With three washers it was opening clearly too easily with pump clicking away furiously (NRV hissing and buzzing angrily), with two washers the pump settled into a rythmic clicking which sounded acceptable. One can hear fuel squeezing through it with the ball buzzing inside as it oscillates from side to side;
3) with one washer the fuel pump would again come to almost stop, so clearly the NRV spring was then too tight - even though free to move.

I therefore settled on two washers. Now the fuel pump no longer comes to a complete stop indicating that fuel is flowing continuously.

When operating my cars, I try to drive the fuel tanks right down to empty, as far as I dare. This I do in an attempt to suck up any dirt into the fuel filters to keep the tank clean. Then I fill the tank and I also add 500ml of two stroke oil (only my old cars) before filling. This 2SO in the fuel has many benefits for these old cars but the 2SO may also help to avoid this NRV getting stuck when standing for a long time.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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#3 Re: Difficult start - only when heat soaked E-Type

Post by jagwit » Thu Mar 30, 2017 4:44 pm

Hmm.... This is becoming interesting!

So, this morning I had the NRV working very nicely buzzing away happily when I had the fuel pump running - with two copper washers. Then I drove to my parents about 25Km away for tea (mostly highway). Starting the car there about an hour later, she still cranked quite a bit but not as much as I expected, so I could not convince myself that there was an improvement worth mentioning.

When I got home I let the car stand for 30 minutes and then switched the ignition on. Surprise!!! The fuel pump again came to an almost complete stop (very similar to the way it did before I started work on the NRV). Listening at the NRV, I could hear fuel flowing in very slow bursts but not as continuous as before. Again it did not start with the confidence I was hoping for. Am I concluding that the NRV is somehow temperature dependent?

Now I fitted a third washer again and now its buzzing away when the pump is running and the pump sure is clicking away merrily. I could also hear what sounded like bubbles being squirted through the NRV.

Not sure when I'll drive it again but will report back soonest.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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jagwit
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#4 Re: Difficult start - only when heat soaked E-Type

Post by jagwit » Mon Apr 03, 2017 2:45 pm

One 50km trip with ONE heat soaked start. I see that some use a bit of choke with heat soaked starts and I have to try that as well.

It did crank longer than a cold or short-off hot start, but not anywhere as long as what it was doing before "tuning" the NRV. I'll have to do a lot more heat soaked starts before I'll know for sure if there is an improvement, but I have now determined that even with a substantial amount of fuel being pumped back to the tank, there is still an adequate amount going to the carbs as I did not suffer any sustained full throttle :mrgreen: fuel starvation issues during this last trip.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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Adamski
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#5 Re: Difficult start - only when heat soaked E-Type

Post by Adamski » Tue Apr 04, 2017 5:28 pm

I have fitted a translucent fuel filter on the downstream side of the valve. This enables me to see the fuel flowing when ticking over.
I suspect there's just too much heat once left and the inlet manifolds are vaporising.
I try to switch the fans on before I stop the engine to cool things down a little. It usually starts on the third good crank over.
Adam
S3 V12 E Type FHC Manual 1972-owned since 1978

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