S3: Difficult start - only when heat soaked

E-Type
1

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?

2

Hi Phil, After that 20 minutes then you have given the whole engine a good “heat soak”. So this might cause a vapor lock in the fuel system, or alternatively the "Opus’ has heated up and has quit working until it cools down. Of course i hope you realize Phil that you might have shared a little more info about the car!

3

Had the same problem several years ago. It was vapor lock caused by the stuck ‘valve’ that allows gas to go back to the tank. It is composed of a ball and spring. Just cleaned it up and problem solved.

4

Where should this valve be Mel?

No OPUS in this car. Running on Lumenition. What other info would you have liked John?

5

Found it. …

6

Well…what yr…does it still have air injection or not…how much of the federal stuff is still on it. stick or auto. The point is that if you feed us info in small bites…we might get fed up and pass over the request.be helpful so we can !

7

Yeah, me, too in my 1971 Series III V12. Mechanic said time for a carb rebuild, and that helped immensely - and in most other ways, too. Another recommendation is to use non-ethanol fuel as it has a higher boiling point than ethanol gas. It could be a float problem, where the float is letting gas drip down into the intake manifold flooding the engine. I’m guessing that when your does start it’s belching our dark gary smoke indicating flooding.

8

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

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 - click on the image for a good look).

tn_20170330_085828.jpg1200×675 96.7 KB

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 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.

9

Interesting - I never thought of the NRV playing that specific role and the need/reason for continuous return flow. I’ll check mine today. When I turn on the ignition, the fuel pump runs continuously, which would indicate the NRV is working properly. New NRVs cost about $48! And new spring goes for about $2. This is from XKS Unlimited.

I’m a bit new to the E-type and am learning when to refill the gas tank. Seems it runs out shortly after the low gas warning light comes on [ask me how I know!], even though the level gauge shows just under a ¼ tank. I generally like to refill at or before the ¼ level in all of my cars to keep the in-tank pump from straining at very low levels and picking up trash. However, I see your point in using the filter to help keep the tank clean.

10

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.

11

All great info as my 74 4 spd OTS had similar circumstances last Summer. Figured out if I gave it 1/4 choke with no throtle it would fire right up. Will chk my none-return valve upon taking her out of storage…Hopefully come May as our Rocky Mt. weather can be iffy at 8,367’ ASL.
Cheer’s,
Todd