Lotus Elan

Engine running troubles

PostPost by: martynw » Fri May 03, 2019 4:32 pm

My Elan +2 has been running poorly for a while, and I'd got into a spiral of not using it much because it didn't run quite right, and therefore it probably got worse because it hadn't run much. I'm determined to sort it out before the weather turns nicer (!?).

It has been blowing a lot of smoke and the plugs were getting clogged up quite fast, so initially assumed it was probably running rich and needed the carbs retuned. However on trying to do that, I've found it constantly hunting with revs roaming up and down whether I am tweaking the tuning or not.

Quick bit of background, it is a mildly modified engine - has a ported head with CPL2 cams from Paul Fisher a few years back, is set up at compression ratio of 10.1:1 and the carburettors were jetted and tuned up on a rolling road at Sanspeed a few years back. We got about 115bhp out of it.

Once my tuning attempts were going nowhere I did a compression check - all pistons are 200-205 psi, so look healthy.

I therefore wondered if oil was getting in through the valve guides - they shouldn't be as the head hasn't done many miles - but removed the carbs to have a visual check of the inlet valves at least. I know twincams are expected to burn some oil down the valve guides, but was a bit surprised to be able to actually see a drip of oil at the bottom of some of the valve guides. There are small but stubborn burnt carbon patches on the trumpet part of the valve.

I've attached pictures and hoping those who have seen more of these engines can advise whether this looks excessive or not.

Assuming it is OK, I thinking my next step may be to refit the carbs - ensuring there are no leaks from the rubber ring/plate couplings, which I guess could have been another cause of the hunting. I'll tune it as best I can and then give it a good 50 mile a-road drive to see if just giving it a blast will clear it out a bit - I'm aware it has spent too long in slow traffic on the last few occasions it has been out, or even just being started to drive it in and out of the garage. Then I'll see if I can give the tuning another go.

Any other ideas of stuff to check out would be appreciated though.

Martyn
Attachments
cyl4-cl5a1025.jpg and
cyl3-cl5a1022.jpg and
cyl2-cl5a1017.jpg and
cyl1-cl5a1021.jpg and
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PostPost by: mbell » Fri May 03, 2019 4:45 pm

Air leak from headlight lift or brake booster?

Are you losing brake fluid?

Is the hunting just at idle it when driving?
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PostPost by: martynw » Fri May 03, 2019 4:58 pm

Just at idle - cannot get it regular. No brake problems, and no major air leaks on lights (they stay up a good while after engine is cut off). Good point though - I'll go through all vacuum hoses.
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PostPost by: rgh0 » Fri May 03, 2019 11:38 pm

It does not look like excessive oil going down the valve guides.

I would look at the distributor and make sure the idle timing correct and is not moving around due to worn bearings or failed springs and the rest of the ignition system is is good condition and giving a consistent spark. As the old saying goes - "most carburettor problems are electrical" :lol:

Once confident the electrical side was Ok I would look for air leaks. I would blank off the vacuum to the headlights and brake booster and ensure the carbs were bolted up correctly. If moving the carbs up and down while the engine idles causes changes in idle behaviour then you probably have the carbs bolted on to loose.

If after doing both these you can still not get a steady idle I would take the car to an old style carb and ignition tuning specialist who knows Webers and ignition systems to see if they can find the problem.

cheers
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PostPost by: 2cams70 » Fri May 03, 2019 11:49 pm

Do a power balance test to see if it's a generalized issue or specific to one cylinder only. Short out each spark plug in turn and note how much the revs drop for different cylinders.
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