The Lotus Grand Tourers

Lotus-e-Clan wrote:Very encouraging!

Was that at Northallerton Angus, or Bogg Brothers @ Malton?

What did they fettle?

Couldn't get an email response from Bogg Bros., unfortunately, so I popped into Motoscope at Northallerton. Little bit of ignition timing, tweaking of the carbs and (bizarrely) reducing the mains from 135 to 130s since it was running *very* rich (enough to mean that I had to clean at least one plug every 2 or 3 weeks).

The main aim was to get rid of rough spots below 3k and improve emissions to the point where it ought to pass MOT in Feb.

Both of those seem to have been achieved, and finding the ponies down the back of the sofa is a welcome bonus.

Interesting. Ignition tweeking is no surprise. The need for mains reduction *could be* explained by a change in venturi airflow /volume. Main circuit will be operational during progression (transition from idle circuit to mains) and definitley a key player around 3Krpm. If air volume through the venturi is slightly reduced but venturi depression is still relatively high then it'd run rich given fixed jetting design. The venturi depression sucks hard on the fuel supply circuits drawing plently of fuel into the given volume of air. Reduction in venturi air flow on induction stroke can be as simple as less air filter flow (eg dirt) - or as complicated as cam timing/tappet clearance or worn rings/bores. But given the good rolling road figures that's not likely.

Alternatively if the acceleration pump circuit is 'weeping', it is additive to the main circuit - so reducing the mains will indeed compenesate, as would fixing the weep - but that is more difficult to detect dynamically. Possible causes for weeping are pump jet 'o' ring issues and pump lever malfunction - the 'biro' spring on the pump spindle may have hardened/rusting or just set too 'keen'.

Anyway that's just guessing. The main thing is that the outcome is positive and sounds like your engine is in good condition given those figures! Happy days!

Well, since this all started when the carbs. were overhauled (including new pump springs), I'm hoping there's nothing fundamentally wrong with them - just the effects of 206k miles of use and the fact that everything's old and has done over 200k miles.

As you say, the fact that the final figures are close to factory spec. suggests it's mostly OK and in the words of the wisest man I ever met - "When you reach the bottom of the 'ole, stop digging".

And, in case anyone's interested, here are some graphs.

Big differences when you see it on paper!

Hopefully they weren't 'sandbagging' on the first run in order to acheive maximum customer satisfaction and a sense of 'value for money'.

I'm a damaged soul mind-you. My 'natural trust' gene was down-regulated by all sorts of bastards in the past who've tricked me.


That said, -you would have definitely felt the difference (or not) going home!

Is it worth while playing with ignition advance or is the standard curve of 10* @1000 rpm, 18* @2000 rpm and 26* @ 3000 rpm the optimal advance curve?

I have a standard HC engine with twin 104 cam's.

I have an Accuspark programmable blackbox so i can program any curve.
26* @3000 rpm seems a little conservative.

Somewhere on here I previously posted an extensive ignition advance map (throttle position, revs, and ignition advance).
Not sure if you could use this as a guide?

Tony

Thank you for your map.

It does not seem to work for my engine, its way to much advance.
No pinging but bad torque and top end power.

I had set 32* as max advance but it was to much, now its 28* max.