S3 "miss On Tickover. Baffling..........

[elans3]

Well chaps, after a weekend of fiddling, I'm no further forward.

[elans3]

Well chaps, after a weekend of fiddling, I'm no further forward. I've added another engine earth and cleaned up the original, fitted another new, Lucas rotor arm, changed the distributor cap for another new spare, checked the valve clearances and for a broken spring, found the best, newest pair of 40 DCOE 18's that I have, (1 brand new, the other almost), changed the mounting o'rings for ones of a slightly bigger dia section to eliminate any chance of a leak from those, checked the timing 2 or 3 times, (static), and finally greased up the mixture screws as Keith advised, and it's still there.

[elans3]

Short of changing the Voltage regulator and dynamo , coil again, and going back to points in the dizzy, I've run out of ideas. By the way, in answer to one of your questions earlier, I'm running Duckhams Q 20/50, and run unleaded with Millers VSP.
It's driveable. but obviously misses when trundling around in top gear at low revs, but goes like a scalded cat when it gets above 1500rpm. In answer to Hatman, its not the camshafts, as it pulls like a train . I too have run peaky cams in these engines before and there never seems to be much of a loss of torque over the standard set-up, just better power at the top end.
Steve

[types26/36]

Steve.
Unless I missed it what was the results of your compression test? if that was O.K. I think its time to book a session on a scope.
Regards Brian.

[type26owner]

Hey Steve,
I'm having second thoughts about Hatman's regression suggestion since really radical cams could be the culprit of the mysterious misfire. Maybe you should try retarding the timing while it's idling and see if that helps. This makes the pressure of the combustion less efficient at an idle since the event happens maybe after the piston starts in the downward direction. You don't really care if the engine is really fuel efficient at an idle anyways since it's not using all that much fuel at that rpm. Expect the Webers to start to spitback when the advance gets around zero. If that is the cause then the fix is to increase the range of the mechanical advance of the dizzy and leave the total advance at about 36 to 38 degrees depending on the boundary of detonation. The spitback can be dealt with by simply fattening up the mixture.

[elans3]

Hi Chaps,
Compression test was AOK, done warm gave very close readings, what you'd expect after a rebuild.

Keith I'll try your theory of retarding it at idle, but don't forget these aren't really radical cams, they're the Super S/E cams on a Sprint head, (Sprint cams in effect).
I'm still convinced that it's something more simple. Just can't put the finger on it yet.
Steve

[type26owner]

If you want to eliminate the really simple stuff then try using different brands of fuel. I can tell if the fuel is junk within one mile of the dispensing it now. Once the carbies are sorted correctly any change is easy to recognize. I've gotten four bad tankfuls from two different brands in the last year alone. Have no idea what was wrong with the fuel just it generally made the engine balky, misfire and pop out the exhaust on overruns. Kinda what it did all the time before I learned to tune it.

One dead givaway that the fuel is sour is if it stinks.

[type26owner]

Hey Steve,
Because the aluminum head is very efficient at removing the combustion heat on the milli-second level timescale if the cooling system temperature is fluctuating constantly the chance of having the idle hunting the rpms and missing is greatly increased. This changes the pressure and thus the force to move the piston derived from each combustion event from moment to moment. Having a cooling system temperature instabilty affects the idle most noticably. Reducing the heat that's being removed by the cooling system if it's allowed to overcool helps enormously to lessen the severity of an idling problem. Damn that entropy!

It's unreasonable to expect the Webers to perform well under that faulty condition.

[type26owner]

Hey Steve,
What you're trying to accomplish is just about the hardest thing to do technically on the Elan. Here's a link to an article which kinda displays the scope of the issues to which you're impacted though the article itself is about advance curves.
<a href='http://www.jcna.com/library/tech/tech0013.html' target='_blank'>http://www.jcna.com/library/tech/tech0013.html</a>

Contrary to every bit to tuning advice which is out there including the info from Weber about setting the idle mixture to the best lean idle to get the highest idling rpm. If you do that then you'll experience that from day to day the idle will be always changing. Somedays it will purr perfectly and others it will tend to try and die. This can be lessen somewhat by ignoring that dumb advice and setting the idle mixture so it's just halfway between being to fat and to lean at the boundarys where it causes a misfire. This gives more of a margin of error by posturing the mixture strength in middle of the environmental bell curve so it lessens the tendency to start misfiring. Highlights one of leading shortcomings of a carbie since the environmental conditions are always changing but the settings of the carbies can't respond. Otherwise you'll just chase your tail forever.

[mikefromengland]

when you rebuilt the engine did you replace the distributor with a new one and are you using the correct one.on replacing mine i solved a mountain of probs overnight.it transformed my car alltogether.my car was horrible to drive in traffic now it drives smooth as silk.kind regards mike

[elans3]

Hi Mike, the engine was rebuilt by the previous owner,and had done virtually no miles. He has obviously done a good job as all indications are excellent, ie all new interior parts as you would expect, vernier cam timing gear, all compressions at 190 psi and all literally within 2 psi, which is very unusual. I have had "his" distributor in it, plus two of my own, both known to be spot-on, but to no avail.
I was very reluctant to change the copper cored leads, as I've run them before with no problems on a similar spec Elan , but I've relented and ordered some today, as I'm running out of ideas. Will keep you posted once they're fitted.
Steve

[elans3]

Hi Chaps, I've just come across this old post of mine, and realise that I hadn't informed you good people what the problem turned out to be. (I know it's five years ago, and I hope you guys will forgive me for not letting you know the outcome.)
It was the day of the annual MOT test, (2006) and I was late picking the car up from the garage, hence it was dark. I had never really used the car in the dark, and noticed on the way home that the headlights were disappearing when I gave the car some throttle.
Trundled home and set to work on the headlight pneumatic system, in particular the non return valve.
Took it out and found that I could blow through it both ways !
Replaced it with a much better quality Norgren valve and hey presto ! Beautifully working headlights, and no engine miss at idle !!!
It was obviously pulling air through from that valve into the inlet manifold, but why only noticeable at low revs ?
Anyway, once again my sincere apologies for not realising that I hadn't shared it with you, but it may help someone else who is experiencing a similar problem,
All the best
Steve
elans3