Anti run on valve

[unicorn]

Hi all when my car is warm and I switch off the engine it seems to run on a few seconds then stop. I read somewhere there's an anti run on valve but cannot find one on mine I have a uk rhd model with standard 2 litre engine. Can someone please post a photo of the valve and where it is supposed to be so I can either find it or fit one if it's missing
Thanks in advance

If it makes you smile it's the right car

[Hasbeen]

Unicorn, I don't know about anti run on valves, I know they were fitted standard to the ZS carbs supplied on 7 for the US, & many OZ cars. I don't know if you could attach something to SUs to do it.

I have always used the "wet out" technique on cars that ran on. It is usually caused by a bit of carbon deposit in a combustion chamber or on a piston, glowing red hot, & continuing to ignite any incoming fuel, after the ignition is off.

The simple answer in the old days, when lower quality petrol burned much dirtier, leaving lots of carbon deposits, & still today when it happens is to cool that bit of hot carbon.

When turning off, give the thing a rev to say 2000/2500 RPM, turn the ignition off, then floor the accelerator for a second or two. The incoming charge will put the fire out on any stray bit of hot carbon, & prevent that run on.

Be sure to get your foot off the throttle a few seconds before the engine stops spinning, so any petrol is blown out the exhaust, & a film of oil can be deposited back on the shiny bits.

Let us know if it works for you.

Hasbeen

[john 215]

Hi,

As Hasbeen say's never seen one on a UK spec SU carbed car.

They were fitted to MG Metro's over here ' back in the day ' and basically opened up when the engine was turned off and killed manifold vacuum.

Cheers John


LIVE LIFE A QUARTER OF A MILE AT A TIME!

1976 Speke FHC BEAUTY FITTED WITH OVERDRIVE GEARBOX

1979 3.5 FHC CURRENTLY GARDEN ART !

1982 2.0 DHC NOW A 4.6, BUILT NOT BROUGHT !!!!

[unicorn]

Thanks both if I get the problem again I will try that hasbeen. I only had this car at the end of last yr and it's only done 200 miles over last 3 years mot's. It ran on when I took it for a run last October. Not taken it out on a long run this yr and have done a fair bit of work on her over winter including work on the cooling system but will be this weekend on a charity run so hoping the work done will have fixed the problem. I didn't have this problem on my previous tr7 and there wasnt a valve on there. The only car I ever had this problem with was my old 2.3 vauxhall Firenza which ironically also had twin SU carbs the problem with that was the cooling system which after I overhauled it fixed the problem so fingers crossed
Thanks for the help and info both, much appreciated
Chris

If it makes you smile it's the right car

[Hasbeen]

Chris I had it badly in my race prepared TR3A engine in my Morgan +4 in the early 60s. The wet out system worked on it. Then the Renault 12 my lady drove for years was bad.

She never could manage the wet out technique. She would leave it in gear, clutch in, brakes on, turn it off then let the clutch out. It sure stopped the thing, but is not a technique I'd recommend.

Hasbeen

[Cobber]

You could always try sparkplugs a heat range cooler, the hot spot may well be the plugs themselves. Hotter plugs retain more heat and cold plugs dissipate the heat more.

"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"

80'Triumph TR7, 73'Land Rover (Ford 351. V8),
'89 Ford Fairlane
'98 MG-F, 69'Ford F250.

[FI Spyder]

The theory behind the anti run on valve was to open a sizeable pathway for air to get into the the intake manifold when the ignition was turned off (drops the manifold pressure as mentioned). This extra charge of air turned the fuel air mixture to very lean such that any hot spot wouldn't/couldn't ignite it assuming you weren't running rich to begin with. Guess it was only needed in emissioned N/A type cars.

- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

[unicorn]

Thanks all I changed the plugs and didn't happen when I took it out. Next problems I noticed a nasty grinding noise when cornering hard and fuel gauge not working. Is there any way of testing a gauge and sender on the bench as I have spares of both but no idea if any of them work ok before I try to fit them. Low fuel light comes on but fuel gauge is staying at 3/4 but drops when ignition off so I'm thinking sender is most likely

If it makes you smile it's the right car

[saabfast]

My gauge was like that when I got the car. I could see that the level unit in the tank was new looking so tried a gauge from a spare dash. That cured it.

Alan
Saab 9-5 2.3t Vector Auto Estate
'81 TR7 DHC

[sonscar]

The fact that the gauge reads 3/4 when turned on and goes off could be due to either the sender or the gauge itself.The gauge has two coils wound in different directions and mine exhibited the same symptoms.A new sender failed to fix it and involved a good amount of work.On removing and testing the gauge one of the coils was disconnected,luckily I managed to repair it.As it is a relatively comfortable and easy task to change the gauge I would try that first(bearing in mind that it too could be faulty).Just my experience,Steve..

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[dursleyman]

Swap the gauge first its a bit of a fiddle but probably easier than the sender unit. Fixed mine that way.

[unicorn]

Thanks for the replies I have 2 spare gauges and tried changing those but both read zero when fitted so I'm assuming they are both faulty. Is there any way to test them when not on the car before I dump them and buy new?

If it makes you smile it's the right car

[FI Spyder]

You can test the sender on the bench with an ohm meter (multimeter). there are three connections. One is the ground. One of the others turns the low fuel light on and off so it should read open or closed depending on the position of the arm. The other connection is fuel gauge. As the arm sweeps the value should change fairly smoothly. I'm not sure of the values as I didn't write them down.

An interesting aside is I soaked the outside of mine with Metalready to get some surface rust off. Some got inside and it is not good for the resistance coil (which I found out when doing it for the dash light potentiometer). and the resistance was not smooth with the sweep of the arm. I put it in any way and when in the presence of gasoline it returned to smooth action and has been fine the last 8 years. The whole system is analogue and the reading is based on the resistance in the circuit. That means even if you have a good sender and gauge you will have incorrect reading if the electrical connections are not clean or wire is broken although the reading will be low (if resistance is high) rather than high.

As mentioned as yours reads 3/4 when it should be lower I would suspect the gauge rather than sender unless the sender arm is some how hung up on it's sweep.


- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

[Workshop Help]

Uhhh, I'd be more concerned about the nasty grinding noise than the gas gauge.

Mildred Hargis

[unicorn]

It's booked into a garage for Friday to investigate the noise I'm just working on the bits I'm more comfortable with and I leave the more major work to the local garage

If it makes you smile it's the right car