Military Lightweight Forum

Hi all,

I am at a my wits end trying to figure out what is going on with my carb or perhaps it is some other issue.
Mine is a late Series 3 Lightweight with 2.25 petrol 5 Bearing engine, 8:1 compression ratio, ducellier distributor and Weber 34 ICH carburettor. Manual fuel pump, seems to be pumping fine. New engine oil, fully rebuilt, fresh coolant in the radiator.

Here is a video of the most recent start I did yesterday. AWFUL.
https://photos.app.goo.gl/m2tuejaRaE34C7Zs9

There is even a dreadful pop at the end and a hiss. I had to press the accelerator to get it to keep going.

History to date:
My old Weber carb had a worn butterfly shaft, so I got a new one from Paddocks.

With the new carb, In the last few months I have successfully started and run on all cylinders, driven the truck and been pretty happy with it's running condition at high RPM and rich mixture. In other words it was functioning at 1.5 turns in of the idle screw and fully screwed in Mixture Screw backed out two turns (factory starting settings).

However getting it to idle on low RPM has always been an issue and now starting it is even not happening.
Here is a summary of all the things I've tried:

I originally fitted the Weber Carburettor with the help of a local expert who used to own and run the local Land Rover service workshop and distribution for Bearmach. But it would not idle properly despite our best efforts. We have eliminated all other possibilities and have even carried out an engine leak down compression test. Everything is perfect but the carb will not idle while following the manufacturer's instructions and settings.

We are only able to get the engine to idle with the mixture screw fully removed (taken out entirely!) and the idle speed adjustment screw more than 1.5 turns in. So it runs horribly rich. We believe it is a problem with the fuel and air flow passage to the lower section of the carb (below the throttle shaft and butterfly plate).

The upper section of the Weber 34 ICH and the bowl and float seem to be okay. There is no fuel leaking into the carb from a fuel level problem in the bowl or with the float. The jets and emulsion tube are all clear and clean. The gasket is seated and we even tested making a tiny cut in the inside edge to allow a hole in the lower casting to not be covered / fouled.

Paddocks have given me a full refund but I can't see how it is not something I can fix or address.

Now I can't get it to do anything really. What you watched above is my best attempt. This was after dismantling the carb and cleaning with carb cleaner.
Could it be the inlet manifold? Could it be a vacuum loss somewhere? Why would it just stop working?

Any thoughts or things I can try are welcomed wholeheartedly.

Thanks all.

Just thinking laterally as a lot of carburettor problems are actually ignition problems.

Check that you are getting a decent spark by holding the king lead 1cm from an earth point then have someone crank the engine. A spark should jump this gap, watching a spark across a plug is not helpful as the gap is very small & there may be no such spark under compression. If no spark until the king lead is only a short distance, then check the distributor condenser or replace it.

Check that the ignition leads are in the right sequence.

Check that the carbon brush inside the distributor cap springs freely up & down so it can rub on the rotor arm centre.

Check that the coil terminals are correct ie that you are running with a negative spark, a positive spark will invite poor running.

Check that the coil is not too hot to touch. If it is there will be insulation deterioration internally & a reduced output.
Check that the CB points gap is correct if not the dwell angle is increased so the coil heats up because it stays on for longer.

Examine the sparking plugs to check that the gaps have a biscuity brown appearance, not oily or dripping with fuel.

Have you tried running with fresh fuel? As for timing I never did it by the book as the book was written in the days when petrol was proper petrol, I adjust the timing to give the smoothest running not the most revs.

Check that the vacuum advance mechanism moves freely. Also check that the points insulating block can freely move on the locating shaft & that it is not binding a little.

Hi Alex,

Clive has mentioned it, (Hiya Clive! ), and I'm not saying I'm right, but from what can be seen and heard it does sound like the firing order may be wrong. Unfortunately the leads/distributor cap can't be seen in the video.

Regards,

Thanks Neil and Clive.
Thanks a million for the helpful suggestions.
I will go through it this weekend and come back with an update. I'm pretty sure the cables are on the correct plugs bur perhaps the cap is on funny ?
Will check
Thanks!

Bonjour Alex,

Sorry, I missed an episode...

Well, I can't do more than Clive and Neil's insightful information.
However, basic comments/suggestions:
- Borrow a Solex 36IV carb and see how the engine works
- You had 2 LWT at the beginning to rebuild one… Maybe another carb available then…?
- No air intake in the intake manifold?
- I see your coil installed vertically: is this normal?
- Do you have a good ground strap between the engine block and the chassis?
- Air filter properly installed?

At the very beginning of the restart of my LWT (Solex 36IV carb and all brand new) the engine was running "rich" and sometimes stalled with the "factory" settings: an old mechanic grandpa adjusted the ignition advance "by ear" no more worries, everything is very stable now.

Bon courage.
Looloo

Hi Neil, Clive and LooLoo,

I think the brush in the brand new distributor cap has fallen out somewhere... I've looked at an image online and from memory all I saw was the little spring behind the brush.
Later on I am going to look for the old cap to test and check the brush is not around the points or inside the distributor somewhere.

This could be the issue. Fingers crossed!!!!

Yessss…!

A missing carbon brush may well upset the spark on it's journey,. Hopefully fitting a replacement will have the engine running nicely.

While you have the cap off it's worth checking for any signs of cracks/tracking in the cap, and cleaning any deposits off of the four plug lead contacts.

Regards,

I put back the old cap with the brush and tried with the old rotor and new one. Still not functioning well.

Things on my list to do:

- I will check the gauze cone on the fuel tank pick up sender to check it is clean and fuel can freely flow upwards.
- I'll also clean up the distributor cap contacts and see what kind of spark I get at the plug end when grounded to the engine block.
- I did already check the coil spark by turning over the engine with the HT lead unplugged from the centre of the distributor and grounded on the engine. Saw a nice bright spark / arc about 6-8mm long.
- I'm not sure the coil facing downwards is an issue as that is how it was before and pics online suggest others run their vehicles this way.
- I have a friend with a different distributor with electronic points which he is going to give me to try.
- I will also get some new fuel that has not been sitting in the tank for 3 weeks.
- I'll clean the spark plugs... again.
- I'll check the fuel pump gauze and bowl for sediment.
- I'll spray some carb cleaner around the manifold when idling (if it idles for more than 5 seconds before cutting out!) to see if revs increase.
- I'm pretty sure the engine is well grounded... but will check.

Hi,

With the loan of your friend's electronic ignition you will eliminate a lot of tracks.

Good road !
Looloo