Car now insured so I dropped the tyre pressures and took my daughter out for a bit of a longer road test.
It ran really well for about 10miles, then started getting very lumpy at idle
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I started messing with the mixture, trying both leaner and richer, but the rough running just started getting worse and worse with each run up and down the road.
I did a bit of head scratching and finally thought this might be down to putting a couple of gallons of normal unleaded in, so I duly went out and bought 21litres of Tesco Momentum.
Further adjustments and more short road tests revealed no improvement - in fact it carried on getting worse, to the extent that it would barely get up to 20mph after a mile or so ... This led to me nearly getting rear-ended so more serious intervention is obviously needed before going back on the main road.
Plugs checked and and one found to be 0.45mm gap, but otherwise all ok.
I re-gapped No2, and re-fitted them, but perhaps unsurprisingly there was no improvement.
It's difficult to describe the symptoms effectively, but as best I can :
"lumpy thudding with no power - ticks over, but will not pull at all" (although it's always made it up to a mile home when running like this, albeit very slow and lumpy).
Fortunately I had planned to go to the Classic Car Show on 23rd March, so took the opportunity to seek some advice from the team on the Grand Tourers Stand. Thanks to Tony, Alan and Richard for your advice. It was good to see you again Tony, and I also enjoyed our long discussion Alan - quite a few things for me to try - some especially simple ones from Alan that I had not thought of before. It's great to put faces to names, and I hope to see you again soon, preferrably with me in a Lotus !
We are now in the last week of March, and the car should have been MOT'd by now, or at least have a to-do list from the test.
Time to get on with some more testing, starting with the simple stuff suggested by Alan :
First I checked the timing. It was around 13 at idle going up to about 29deg BTDC above 3,000rpm. This is now adjusted to 9deg and 25deg respectively, as per spec. Doing this also enabled me to check whether the ignition advances as it should, which was one of the simple tests Alan suggested. All seems good in terms of the mechanical advance, unless it is potentially sticking on a proper run, however I'm thinking this is unlikely as I've tested it with the engine fully hot. No perceptible change in running following the timing adjustment, but I didn't really expect that to change much based on the symptoms.
Disconnecting the rev limiter didn't seem to make any difference, although I will confirm this on a longer run if I don't manage to solve things elsewhere.
Back to suspected fuel issues - I checked the carb inlet fittings, expecting the little filters to possibly be blocked - this was my most promising option so far based on the symptoms. There are no filters in these fittings, so that's another thing ruled out. Also, I tried to order new ones from SJ, but it seems they are no longer available from anywhere ?
Time to start stripping the carbs, and soon started to find some issues - I think the pictures tell most of the story :
Check the idle jet o-ring
Not sure what's going on with these jets, but more importantly, check the old fuel varnish in the bottom of the float chamber
Time to bite the bullet and take the carbs off for a proper inspection and service.
Then saw the condition of the spacer o-rings - definitely not helping, but probably not the only problem.
I know the pump chamber non return valve is critical on these carbs and can be prone to sticking, especially with old fuel, so stripped off the bottom end and found lots of debris in the pump cover assemblies. One carb was much worse than the other for some reason, which is maybe why I don't get a total failure with the rough running ?
Also, I'm thinking the detergents in the new fuels have gradually started to break up the old varnish and that might be why it's getting worse ?
Internals now all cleaned out and waiting for o-rings from SJ (idle jets, pump jets, and spacers). Interestingly, Eurocarb say the normal 45DHLA spacer o-rings won't fit a Lotus due to the spacer grooves being too deep - they recommended going to SJ or Lotusbits for this part. Having taken some measurements I'm not entirely convinced, but I ordered from SJ in any case to be on the safe side. They also sell the internal carb parts I needed, so that saved a bit of postage.
Carbs now awaiting o-rings before re-assembly and test.
While the carbs are off I also took the opportunity of looking in the distributor for any evidence of loose/damaged wires :
All looks ok I think, but I'm not sure I can see the bit that other people have reported problems with ?
I was half tempted to take the distributor off and strip it down while the carbs are out of the way, but I'm not so keen despite Tony's re-assurance on the simplicity. Hopefully I've found enough other contributing factors to fix the issue.
With a bit of luck I will have the car re-assembled next week - I'll report progress (or lack of) after taking it out.
In the meantime, if anyone has any other thoughts, advice or suggestions based on the pictures and description of symptoms then they would be gratefully received.
Cheers all and thanks again to Tony, Alan, and Richard for the advice
. After much searching I managed to find a straight swap for the pump, so no major issue in the end.
That's a good test to have confidence dizzy pick up is good. Allows you yo focus on the carbs.