running out of juice?

[RobCapper]

just a quick question... I've been flicking through some of the old postings etc, and it strikes me that people's twinks are reving quite high (8000?!)

Mine runs out of juice by 5000 ish, and i'm lothe to push it further.

1. should I?
2. why could this be? would better airflow help? perhaps fittting a filter a la cliveyboy?

[1964 S1]

I'd check the points gap, if you have them... and/or all the ignition system... make sure your cam timing marks are correct.... and I'm sure many other ideas will follow. I wouldn't push it further until the problem is fixed. My twinks don't really start to come on until about 4000, and 5000 passes in the blink of an eye. 8000 is a stretch for stock engines but you should not be peaking anywhere near 5000. Check the timing??? Is your distributor tight? Has the car always acted like this???

[reb53]

Is your tacho reading correctly?

Ralph.

[MintSprint]

Hi Rob,

Unless the bottom end is fairly expensively modified, there's a serious risk that the Twin Cam will go BANG (usually by throwing a rod) at anything over about 7,250rpm, so the standard rev limiter is set to cut in at about 6,750 (they're a bit variable, being reliant on centrifugal force against the tension of a little spring). For most people, 6,750rpm is a good rev limit to stick to unless you are racing.

When you say the engine 'runs out of juice', what are the symptoms? I'd expect it to be iginition related, but that would feel either as though the engine's response suddenly becomes very wooly, or a stutter sets in.

It could be carburation or something as simple as the fact that you are not getting full throttle.

If you are at Cheltenham, I'm just down the road from you (near Dursley), so if you want to go for a ride in my car to compare the engine response, give me a shout. Mine is slightly non-standard (QED 420 cams and a head allegedly ported by Brian Hart), but it would provide some sort of baseline, perhaps?

[tdafforn]

I had my twink (+2s130) tuned on a rolling road (aldons) just over a year ago (67K miles from new, original engine, no rebuild apart from new guides, valves and seats in the head).
It produced 112 bhp max at around 5800 rpm, which was a little depressing.
The situation didn't seem to improve with changes to ignition timing (Aldon ignitor), and the mixture was pretty spot on..
I am hoping that being down on power was due to a tired bottom end, it did drink a lot of oil (although it was hard to know whether it was due to the many leaks!). Taking the bottom end apart showed reasonable bore wear, which matched with the excessive crankcase pressure I had.

So am in the process of rebuilding a 711m block for use in the summer...

The question I suppose I am asking is would worn bores lead to a reduction in power and that max being at lower RPM?
Cheers
Tim

[hatman]

people's twinks are reving quite high (8000?!)

Mine runs out of juice by 5000 ish, and i'm lothe to push it further.

I had a similar experience with my car a year or so ago. When revving it out in the gears I found that it really didn't want to know north of about 5.7K, misfiring and being generally unhappy - up to that point it ran like a good 'un. I suspected a duff rev limiter but it turned out to be a knackered distributor, causing spark scatter at higher revs.

The dizzy was so far gone it couldn't be re-built although it had only been fitted to the car some 20K miles earlier (by one of the highly-regarded 'old-school' Lotus oufits! ) and had to be replaced. The engine now soars up to (and beyond) 7K revs, pulling like a train all the way.

Must be worth a look at.

[gjz30075]

I like Ralph's idea of checking the tach for accuracy and also, make sure the throttle plates are fully open when the pedal is on the floor. I'd also check cam timing. If the teeth are worn on all of the sprockets, jackshaft and crank included, that could throw cam timing out enough.

[reb53]

Just remembered having a similar problem on my other car a few years back, ( no, not a Lotus and I'm too embarrassed to say what.)

Pinked like crazy until I re-timed it and then it ran out of power when getting up the rev range. Nursing it along would slowly get the revs up but reluctantly and absolutely gutless.

Turned out to be a seized centrifigal advance on the dizzy.
Should have checked it but assumed it was all done by electrickery.

So....does your timing light show things advancing as they should?

Ralph.