2.25 petrol rough idle

Popped my 1985 LR 90 2.25 petrol to my brothers house round the corner to tune it up as it was running rough on idle. We set the timing first, plugs looked clean, so a spark was good.
Cap looked loose fitting and the rotor arm was all over the place so...
1 new distro cap. Not fixed
One of the cheap leads came apart so..
1 new set of leads. Not fixed
Electronic ignition did not rotate on advance...very odd so
1 new complete distro with electronic ignition. Not fixed.
checked webber carb, this is new, all was good there.

One thing we noticed, the vacuum pipe from the carb still had vacuum on tickover? Did not know this should be the case and can only imagine it may be why it's running rough.
Considered taking the rocker cover off and checking the valve timing to look for clues of maybe a loose cam or timing chain woes, but the darkness came, so I'll leave it for another day.

so driving the 2 miles home last night and it got rougher quick. 1mile on and it stopped, it seemed like it was not getting fuel. One tow home later and left to stand for 10mins, it ran...still lumpy but ran. Now, the other week I did a service and noticed the fuel filter bowl had brown **** in the fuel, so a new filter went in. When I get home from work today I will check that bowl again, then maybe blow out the main jets in the carb and check the fuel flow from the pump. Maybe the failure last night is a seperate issue as it never happened before. I'll be happy to go back to the lumpy tickover for now.

Thought i'd pop it on here to get other opinions. Any other suggestions are gratefully recieved.
edit 27/7;
The plot has taken a left turn now. I cleaned the fuel filter, (that was clean fuel now), added an inline filter to keep an eye on in front of the carb. Fuel pumping through lovely and clean and at a good rate. Pull each jet out and cleaned it, they were fine. it ran rough on tickover still so I took it for a spin, then it died up the road...this time it would not start at all.

Pause for back story; when I first got this a few months back, I was happily driving when a fire started under the bonnet. This turned out to be a shonky wiring job on a security switch under the dash that someone fitted and it shorted out the wires going from the coil to the carb and caught alight. I fixed those wires and made the shonky wiring good for now with the view to remove said stupid switch another time.

So, with that in mind, whilst waiting for a tow, I noticed the shonky wiring came from a harness that goes around the back of the engine, that has damage too.
I then ran wire direct from battery to coil and see if I got a spark, no spark. I'm thinking it could be 2 things.
1) The coil is trashed, what with all the shorting and trouble it's had, not suprised
2) the new distro I fitted with electronic ignition is actually faulty...hard to believe but I'm told this can happen. I may fit the old coil again and see if that works to eliminate that issue, or swap out the little red pickup sensor....these have been known to be faulty out of the box.....I know, hard to believe this one.

I'm now going to see if I can get a new coil quickly. I will indeed run through everything when I get her back in my garage and up on the ramp, currently I'm working on it on the drive with little space either side, so will go through everything eventually. Most classics I have owned go through a period of finding out what has/hasn't or has been done badly historically. It's been a long time since I've had to be towed home in a classic...so I'll get there when I understand everything about this car.



PS: anyone have the timing for this 2.25 engine, the LTP3003 manual is a bit expensive to get this week! We set it as TDC as per other manuals but were left a little perplexed as to if this was right or not. Be nice to have reference to the dynamic timing. In any case, I think the timing is not the issue here.

Brown in the bowl Better have a look in the tank.

1. Buy manual for proper maintenance - try eBay/Amazon for a second hand copy, they're only a fiver.
2. ensure fuel system is crystal clear, new fuel and filters, no blocked lines.
3. make sure distributor is 100% good [do not buy cheap parts, go to the Distributor Doctor for correct parts].
4. set up timing correctly.
4. set up valves clearances.
5. clean and set up carbs.
6. take for a good run to your preferred watering hole, sit back and enjoy.

Job done.

First of all, drain the fuel tank and look inside. If it is rusty, remove the tank and clean it out. To clean rusty fuel tanks I use 5 litres of white vinegar and 2-3 table spoons of baking soda. Pour the mixture into the tank, seal it and shake the tank vigorously for a couple of mins, leave to stand for 5 mins and repeat. Then empty the tank and rinse thoroughly and leave it to dry. I have sometimes used a 2 part epoxy tank sealant called Flowliner but if the tank is not too corroded I usually don't bother.

After sorting the fuel tank I would then check the fuel lines are clear and remove, dismantle, and inspect the fuel pump. While I have it dismantled I would refurbish the fuel pump with one of the refurb kits that are widely available. If you have an inline fuel filter I would also replace that. After the fuel pump I would turn my attention to the carb. Remove and dismantle it and check all the jets are clear, check the float height is correct and check for any wear or play in the throttle spindle. If any part looks worn or corroded then get a refurb kit for the carb and rebuild it.

Having now eliminated a fuel problem I would check the cylinder compression. On a cold engine you should see around 120 psi but this will vary. The important bit is that all the cylinders are within 20 psi of each other. A common problem is the head gasket failing between cylinders 2 & 3. If the compression is fine then you need to look at the ignition system. If you have abnormally low compression on any cylinder then take the rocker cover off and check the valve clearances. If the clearances are ok but you have low compression then take the head off and check for burned or leaky valves and a cracked or warped head. A failed head gasket should be easy to spot. If you can't see any problems with the head or gasket and have low compression, then take the head to a specialist for pressure testing and refurbishing. When you refit the head re-check the valve clearances as the new gasket will have a different thickness to the old one.

After eliminating any fuelling problems and with good engine compression you need to check the ignition. Start by getting the timing roughly correctly set. Set the engine idle speed so to approx 700 - 800 rpm. I use the charge light as a guide, I adjust the idle speed until the charge light is just glowing slightly or flickering if you have uneven idle. Disconnect the vacuum pipe from the carb and cover the hole. Attach your timing strobe and set the timing to approx 6-10 degrees btdc, this may be best guess if you still have uneven idle. After setting the timing, check your plugs, just because they look clean, it doesn't mean they are sparking correctly. Check the gap and check they are actually sparking strongly and correctly between the electrodes. If you have a weak spark or sparking anywhere other than between the electrodes, then replace the plugs and check. if still no joy check the leads are correctly connected and replace if they are in any way worn, corroded or the insulating is cracked or split. If you are still having problems, you need to look at the dizzy and coil. Check the vacuum pipe is fitted and is not leaking or kinked. Check the distributor shaft for any play, either rotational or lateral, if there is any play, replace it, I have had a new distributor fail within 6 weeks so just because it is new, it does not mean it is good. Check the distributor cap for cracks and worn or burned electrodes and check the rotor arm for wear and play. Ideally I would fit a known good distributor and compare them. I would now check the coil, check the leads between the coil and dizzy are in good condition, any joints are tight and that they are no longer than they need to be. If you can, check the coil with a known good one, but I would probably change the coil as a matter of routine. After this, and assuming you have a properly running engine, you can set the ignition timing accurately. I use 99 octane petrol only and have set my timing to 10 degrees btdc at about 750 rpm.

Having checked all of these you should now have a properly running engine. If not I would then look at things like a worn timing chain or crank and camshaft wear. The thing I have found with these engines is that poor running rarely has a single cause, it is most often a combination of several thing becoming worn and out of adjustment. Unless the engine is very high mileage, or you have oil pressure problems then the problem is unlikely to be anything internal or serious, it is most likely to be one or more ancillary parts providing fuel or spark. Just eliminate one cause at a time, fuel, compression and spark and don't assume that a new part is working correctly, always try and compare it to a part that you know works correctly.