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I'm pretty sure that and the diesel variant are the only ones available Paul. I can't see it will do any harm and it's on offer at Halfords right now at £5 for a 500ml bottle.

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I bought a 4A a couple of years ago that suffered from running on. The previous owner claimed it was down to the high compression cylinder head.

It was fitted with H6 carbs and when removing the damper I could see fuel welling up through the jets. After a fair bit of research I replaced the jets, needles and valves. The car was fitted with an electric fuel pump at the back of the car. Apparently an electric fuel pump can supply fuel at up to 6 psi pressure whereas the original mechanical pumps run at somewhere around the 1.5/2 psi. So I ditched the electronic pump and bought a new mechanical pump. At the same time I replaced the pipework which was rubber all the way from the back of the car to the front (fire waiting to happen!).

It hardly ever runs on now, I put it down to changing the fuel pump - often original is best.

I also only ever use Shell Nitro.

Worked for me.

Edited by BarryG
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Interesting, Barry. My car also has an electric fuel pump. When the enging was overhauled in 2007, it looks as if the then owner tried to maximise output by removing the mechanical fan and fuel pump. I'll bear this in mind, although for the time being I'll follow up on the other key suggestions first.

 

Best wishes Willie

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Quick update - just started the car for monthly-ish warm up during the winter. Smooth tickover at 70C, blipped throttle and turned off. No run-on. However, realised fan had not kicked in. Restarted and ran until fan cut in. Then blipped throttle and switched off - obvious signs of "chuffing"! I haven't tried Redex yet and will definitely do so, but not until I take it for a blast. I will also follow up on the action of the electric fan and Peter's recent pressure regulator item. Hats off to you guys, you certainly seem to have put me on the right trail!!

 

Best wishes Willie.

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Quick update - just started the car for monthly-ish warm up during the winter. Smooth tickover at 70C, blipped throttle and turned off. No run-on. However, realised fan had not kicked in. Restarted and ran until fan cut in. Then blipped throttle and switched off - obvious signs of "chuffing"! I haven't tried Redex yet and will definitely do so, but not until I take it for a blast. I will also follow up on the action of the electric fan and Peter's recent pressure regulator item. Hats off to you guys, you certainly seem to have put me on the right trail!!

 

Best wishes Willie

Willie, To complete the test logic: run it up until the fan is running, disconnect the fan then switch off. If it still runs on then its not the fan. If it does not run on it points to the fan lighting sparks.

Peter

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I did try a fuel regulator Peter, I bought a Filter King one. It certainly helped but it never completley stopped the run-on. What I did not like with the electric pump was the banging when you turned the ignition on, plus it worried me how the previous owner had run the power cable to it.

I'm sure there are often more ways to skin a cat ????

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Guys

 

This is sort of related.....Having fitted a replacement mechanical fuel pump to my 4A, I had a problem with "running on" and chronic float chamber flooding.

 

I tried all the usual measures but it just seemed that the fuel pump was pumping out too much fuel!

 

I fitted a regulator, as per Peter's suggestion above and I have to say the car runs more smoothly, the float chambers do not overflow and the "running on" issue has disappeared

 

For me, a cost effective solution.....worth a try!

 

Cheers, Nick

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The strange thing is you would have thought that the float chamber valves would stop any more fuel getting into the float chambers irrespective of pressure. I fitted Grosse ball valves (at least that is what I think they were called), when I researched it they were considered go be the best.

I do remember when I first got the car and removed the carbs dash pots, you could see the fuel welling up through the jets and then running down into the cylinder head. This was with the ignition off ie the pump not running. So begs the question how can that happen?, it would seem that pressure is retained between the float chamber and the jets.

My logic when I bought the mechanical pump, I also bought a spare repair kit which is nice and small and fits in the toolbox, whereas an electric pump would require carrying a spare pump.

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The f/c valve will open if the feed pressure is too high. I think SUs need no more than 2-3psi

The fuel surface in the f/c is at atmospheric pressure so weeping at the jet indicates the fuel level set too high. The f/c inlet valve is in effect a constant level device like the ballcock in a domestic water tank.

Peter

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Brilliant, thanks for the explanation Peter, that makes a great deal of sense. I do remember I considered playing with the float level at the time, but dismissed it as the manual referred to bending what connected the float to the pivot using a certain diameter bar as a type of 'feeler gauge'. I dismissed making this adjustment as the diagram in the manual was not the same as my float arrangement. From what you have said though it would appear essential that if you have an electric pump you will have to fit a pressure regulator otherwise fuel will continue to flow. It does appear to be a very common problem though. I think by switching to a mechanical pump I have achieved the correct end result.

Once again thanks for the explanation Peter I have learnt a lot.

Coming to an online auction site any day now one fuel regulator and an electric fuel pump. ????

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Thank you Peter for the reminder about isolating the fan. I'll see what I can achieve later. My car as a late TR4 has CD175's fitted. With my wife's eager assistance we replaced both the floats and fuel control valves late last summer. Glad I did as the valves were slightly different! No smell of fuel now, so I assume the electric fuel pump isn't the major contributor. Any thoughts on the max pressure setting for CD175's? I assume the regulator is graduated to achieve an accurate setting.

 

Willie

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Update for Peter Cobbold - I took the engine up to temperature and waited for the fan to cut in. It "chuffed" once or twice,but not every time. Disconnected the fan, and it stopped cleanly each time. Conclusion, it seems to be the fan!! I will still add Redex to the fuel and would appreciate it if anyone can send a clear wiring diagram for a cut-out switch [Kenlowe fan, negative earth]. The other helpful comments I will keep under review and will use if there is any hint of a recurrence.

 

Best wishes to everyone Willie.

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An additional point came to light late last night down the pub. An electrical engineer overheard me talking about the running on, and the fact the fan was the problem. He lost me in the technical detail, but he appeared to recommend inserting a diode in the line to act, as he defined it, as a kind of "electrical non-return valve" to inhibit what the fan is doing. Does this make sense to you guys in the know? A confirmation of it being a good idea or not would be appreciated. Maplins sell them, many at £0.09 each, so very cheap!

 

Willie

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Hi Willie,

I was thinking something similar yesterday.

A diode inserted in the positive feed to the fan would certainly stop any voltage/current being fed back from the fan when working as a generator.

The fan could take up to 20amps when switched on - this is what you have to cater for.

When spinning as a generator it would be very low current.

 

However this is only the situation when the fan is wind milling (not under power) and in this condition the relay should be open circuit.

So more thought required.

 

You do have it working through a relay.

 

Roger

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Thanks for sharing your thoughts Roger. I'm thinking the design will be for me to have an override switch with which to cut power to the fan immediately prior to turning the ignition off. The car already has an override "On" switch, and I see Maplins do a toggle switch decorated with "On/Off" so just a case of ensuring the switch is set back to "On" when firing up. My brother is quite adept at making up circuitry, so the exercise will stop him getting bored! He has already created dual-purpose circuit for pause wipe [1 to 25 secs] as an alternative to wipers On constantly. [Just operate existing switch or rotary one].

I don't have a radio, so the blanking plate offers plenty of space for extra switches.

 

Willie

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If you have a relay between the switches, & the fan then you can wire the main (heavy current) feed to the relay from a circuit which does not go through the ignition switch. The fan is then isolated from the ignition circuits.

 

Bob.

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  • 4 weeks later...

Hello All,

 

People mention that the electric fan can act as a dynamo, but is it not the case that the heater fan motor can do the same?

 

Many years ago I had a Herald, and if I had the wipers and the heater switched on when I turned the ignition off, the wipers would continue for almost a full sweep, until the heater fan stopped spinning.

 

Could that produce enough current to fire the plugs?

 

Charlie D.

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  • 2 weeks later...

Hi, I agree with all of the previous suggestions but a couple of other points to check that may be contributing to the over run problem. Possibly obvious but worth a check! Check that the idle speed is not too high and that both carburetors are in sync at idle. Check that the ignition timing is not retarded and that the auto advance and retard is operating correctly. If the ignition is retarded then the exhaust valve may be getting hot enough to ignite fuel. If you still experience the problem with the over running when you have sorted any ignition isolation issues(fans etc) I would definitely check the timing! Hope this helps! I have always allowed an engine to tick over at idle for a short time (10 sec or so) before switching off. Good luck!

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