Over fueling on a pi

Engine Oily Bits, Ignition, Fuelling, Cooling, Exhaust, etc.
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Wolfrace1973
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Over fueling on a pi

#1 Post by Wolfrace1973 » Sun Oct 17, 2021 2:36 pm

Hi, my sparkplugs are black from, I guess, over fueling, all of them. This is causing a weak spark and not starting. The choke cables fully retract from the throttle and mu. New spark plugs started the car immediately but after being run for a while we're black again, idles OK at 800-1000 rpm,. How can I adjust on a mk2 pi please

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Alec
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Re: Over fueling on a pi

#2 Post by Alec » Mon Oct 18, 2021 2:10 pm

Hello Wolfrace,

the Lucas injection system only works properly if the rest of the engine is set correctly. That said you probably don't know what been done to it in the past or even if it is the correct unit for your engine..

However, make sure the plugs and points, if still fitted are right, timing is right and also check the air cleaner is clean.

You say the choke cable is free but the overfuel lever needs to be clear from the actuating spindle. Unfortunately this is very difficult to see as it is on the block side of the metering unit. If you disconnect the choke cable from the overfuel lever, pull the lever forward and you'll feel resistance which is the lever enriching the mixture setting. There should be some free play (just a little) from full off to starting to apply choke. It's easier to do than explain.
Is the engine in good general condition?

Let us know how you get on.

Alec
0465

MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.

Tinsmith_Skippy
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Re: Over fueling on a pi

#3 Post by Tinsmith_Skippy » Tue Oct 19, 2021 8:33 am

I would check your vacuum pipes to see if they are letting air in.

A simple check is disconnect the pipe at the air adjustment screw and put your thumb over it, it should stall the car, if not you have leaks either the throttle body butterflies or vacuum system.

Most checks on the pi are vacuum and pressure related. These gauges are worth having to highlight problems. The car at idle the vacuum should read around 13 hg. If the reading is low then it is a good possibility there is a leak or the engine is not producing the vacuum.

To find leaks You can temporarily disconnect the brake and distributor vacuum lines plugging the outlets on the throttle bodies. Put jubilee clips on the metering unit vacuum pipe to ensure there is a good seal. Bear in mind if you are disconnecting vacuum distributor you will have adjust the advance to 8 deg or slightly more if it sounds right. Process of elimination reconnect the vacuum pipes to find if anything is leaking. If the engine is not producing enough vacuum at idle then it would pay to get the metering recalibrated work under your vacuum conditions.

There is the red training book by Lucas which goes through the aspects of the system.
Link Here
http://www.tr6pi.com/Lucas%20Petrol%20Injection.pdf

I’ve added this link to some photos of the gauge I’ve made but a brass tee is just as good to make one.

https://photos.app.goo.gl/KixrhmvP1g6mAX74A

All best Ross

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david_lall
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Re: Over fueling on a pi

#4 Post by david_lall » Tue Oct 19, 2021 10:00 am

Clean the plugs with a wire brush and check their gap. Also convince yourself that the electrical side and timing is fine. Let's also assume all the vacuum hoses are in good order and the tappets are correctly adjusted.

If the MU (Metering Unit) is over fuelling there won't be any issue starting with clean plugs.

Once the car has warmed up listen to the exhaust, you'll hear and smell if it's rich. It might not be too bad but when you drive you'll feel a lack of power especially going up hills. Down hill probably won't be an issue. A full throttle blast on the motorway will probably make you think things are getting better...

If all this happens then you'll have to reluctantly accept excessive wear inside the MU and it'll need an overhaul.... From experience it needs doing perhaps every 50,000 miles - sometimes more, sometimes less.

The symptoms you have described do suggest you've pretty much done the above and that the second fueling band in the metering unit is over fuelling.... It does have minimal adjustment but tbh they don't go out of adjustment and it's highly unlikely it was originally set up incorrectly. I'd be almost certain something is worn and needs replacing...

... Personally I'd recommend Prestige Injection now being run by Carl, send the MU to him for a proper overhaul
David Lall

1972 Triumph 2.5 PI Estate Royal Blue
1968 MG 1300 Saloon Connaught Green
1978 Carlight Casetta Caravan
http://carlightrestoration.blogspot.co.uk
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Wolfrace1973
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Re: Over fueling on a pi

#5 Post by Wolfrace1973 » Tue Oct 19, 2021 11:25 am

Thanks very much for all your feedback, when the weather breaks I'll go through all the suggestions and report back.

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