Engine won't rev above 5700rpm, suggestions?

[adigra]

Good evening chaps.

I have a bit of a puzzle to solve and would appreciate some suggestions. My car runs fantastic and pulls like a train until it hits a softish wall at around 5700rpm. It's on Webers, Aldon ignition, mechanical fuel pump. I don't have a rev limiter fitted (no limiter rotor arm either). I called a Lotus expert who suggested the weights in the distributor might be seizing, but I think I am right in thinking that they fully open much before (3000rpm?), and the car runs so well that it seems a bit strange. I squirted some WD40 on the weights and springs just in case, and everything looks quite clean inside.

Anyhow, I was running through other various issues which might cause this and to me it seems like a fueling issue rather than spark (but I could be entirely wrong, of course). Does it make sense that the fuel pump is being defeated at that engine speed? Or could the carbs be an issue?

I would appreciate any suggestions regarding tests I could do to determine what might be the cause of this.

Thank you very much.

Adi

[AHM]

mechanical pump? Have you cleaned it out recently?

Carb float levels set correctly?

Choke size?

[rgh0]

Hi Adi

A range of things to look at that I would try. I am assuming this is a recent problem and that previously it has revved out to 6500 with no problem and you have done no recent work on the engine. If there has been recent work done I would investigate whether any of this is the source of the problem first.

I also presume your tacho is accurate and you are not really going a lot faster in revs than you think

1. Check that the ignition is timed right and achieving the full advance specified for your setup. It is possible that it may be jamming in its advance range and not fully advancing and you see this as the symptom you describe.
2. Check and or replace all high voltage wires, rotor, dizzy cap, coil and plugs. All of these components can break down and give problems at high revs. hard to diagnose without the right test equipment so generally easier to just replace.
3. Check for blockages in any fuel filters fitted including the inlet screens in the carbs.
4. The fuel pump should not be running out of flow capacity but if one of the valves is leaking then it may require a pump overhaul or replacement.
5. Check for a blockage in the inlet in the tank as this could be restricting flow. Blow back into the tank with air and / or rod it out with a flexible wire and look in the tank for any significant amounts of dirt or rust or scale.
6. Check for blockages in any of the carb jets. A single main jet blocked may cause this sort of symptom.

Generally something in the above will fix it

cheers
Rohan

[billwill]

If you recently reassembled it, you may not have lined up the camshaft sprockets correctly, so your valve timing may be wrong.

[adigra]

Thank you very much guys, I really appreciate it. I will, hopefully, start eliminating the various things tomorrow and see how long it takes me before I run out of expertise and seek professional help.

The car has been on the road for a little over a year, but to be perfectly honest, I've been so scared of over-revving it, that I've been short shifting at 5500-ish most of the time. After the installation, the engine was set up at Paul Matty (along with having the electronic ignition fitted, etc.). And, as I said, it's so strong and runs great...

Anyhow, the engine hits a wall under power at about 5700 RPM, and it feels just like a soft limiter. It runs strong and then it bounces off that limit (but it's a soft bounce, not a sharp cut out).

Again, thank you!

Adi

[RichC]

am I just imagining it or was there such a thing as a rev limiting rotor arm ?
I seem to remember seeing a great big rotor arm when I first examined my dizzy...

[RichC]

doh! just noticed u have electronic ign!

[john.p.clegg]

...even with electronic ignition the rotor arm (rev limiter) could be cutting in early..

John

Edited

[rgh0]

Hi John
He says no rev limit rotor arm in his first post

cheers
Rohan

[robertverhey]

If it has been playing up since Paul Matty installed the electronic ignition, should they not be approached to diagnose and resolve?

Robert

[Bugeyed]

Is the electronic ignition set or programmed for a rev limit.
the electronic ignition can be monitored by an ignition an
anyliser, if you know some one who is electronic they can monitor it with an oscilloscope and a bit of aluminium foil over the leads.

[Mr.Gale]

I had the same problem on an XKE a number of years ago and it turned out to be the fuel filter.

Mr.Gale

[adigra]

Well, since cleaning the distributor, the car ran perfectly fine today. I suppose I could've inadvertently fixed whatever else it could've been just by unplugging everything and making sure it was connected properly. I'll keep a close eye on it, but 4 hours driving today and no issues what so ever.

Thank you all again for the advice. If the problem returns I'll continue down the list of suggestions.

Regards,
Adi

[robertverhey]

Something has occurred to me in re-reading this and your other thread. Was the car converted to negative earth at the same time as the electronic ignition was fitted? And if so were the two coil wires definitely swapped over, as they need to be? The symptoms described here seem consistent with the coil being connected in reverse, ie the ignition spark is running through your high tension system in the wrong direction. It's all well described here
http://www.lotus-cortina.com/electric/convert.htm

Robert

[adigra]

Hi Robert,

That is an interesting point. Yes, the car was converted to negative earth while it was being rebuilt, so the whole thing went back together at the same time. It was put together at Paul Matty's, so I didn't really think about it. It was running pretty good up until recently though, so I don't know. As mentioned in the other thread (sorry about starting two of them, it was very late at night and I was exasperated), I'm taking it to Kelvedon and will let them figure it out.

Thank you for the ideas though, i am really happy to be learning even if I'm being a bit slow. Every day it's a new lesson.

Regards,
Adi