Engine not revving. Now running fine

[ETTony]

Lads, help needed in deepest Devon.

This last week I received my V5 so of course I have been out and about.

The engine under load will not rev past 1800rpm.
Fuel, I have opened the glass filter, checked the pump clean and it works (could be weak?) and pulled the tank suction, no problems found.
Carbs, I have redone the tuning as per the manual.
Ignition, replaced the new coil with another new coil, dissy looks OK inside (conventional contact points, new) HT leads and plugs checked. LT leads to coil secure.
Car starts on the button and ticks over smoothly.

As an aside my voltmeter shows no charge, so will get another 4TR. I cannot see this being associated with the engine. ( I do charge the battery between test runs)

What is next guys, I am running out of ideas. What is the wisdom of the forum collective ?

Thanks in anticipation.

[cactusman]

Will it just not go past 1800 or does it start to stutter and misfire when you get to 1800 rpm.

If the former it could just be timing is miles out or even a glitch in the pedal linkage although very unlikely...easy to check though...do the butterfly valves fully open if you push the pedal to the floor.

If it starts to misfire at 1800 under load then again it might be a timing issue. Fuel starvation could be the issue. Check the small filters in each banjo union at the float chambers are not blocked. Check that the float levels are correct....I am assuming here that you have SU carbs.
Misfires though are usually down to the ignition system so maybe the rotor arm is breaking down....loose wire somewhere...if you have suppressed plug caps check their resistance between the wire inlet and the plug top connection is around 4000 to 10000 ohms...the modern repro champion ones are not entirely reliable....I have had two go open circuit.

Hopefully the carbs are set correctly and not too lean.

Sure others will have inspiration too and hopefully you will be sorted soon..

[cactusman]

Incidentally I doubt the charge issue is the cause as so long as the battery voltage is 12 volts once started the spark uses little power and the fuel pump will probably stop before the spark fails if the battery is flattened....assuming here you don't have some fancy electronic ignition like the 123 distributor.

[Mark Gordon]

Incidentally I doubt the charge issue is the cause as so long as the battery voltage is 12 volts once started the spark uses little power and the fuel pump will probably stop before the spark fails if the battery is flattened....assuming here you don't have some fancy electronic ignition like the 123 distributor.

I'm running a 123 dizzy. A few years ago, my alternator died while I was miles from home. I had to drive home on battery alone, with a stop along the way to recharge the battery. The dizzy kept firing until the battery voltage dropped too low to keep the fuel pump running and I ran out of gas to the carbs.

[Heuer]

Tony is using a standard dizzy with points.

My questions are:
1. Will the engine rev above 1,800 rpm when not under load?
2. Under load at 1,800 rpm what happens - stuttering, misfire, revs smoothly but sits at a fixed revs?

[cactusman]

Yep...'re read his post and saw it is all standard....my questions exactly....could be almost anything...or a combination...

[ETTony]

Thanks for your comments so far guys.

At 1800rpm, I get misfire thro carbs and zorst.
Under load it will not rev through, light throttle it will rev to 2000rpm but no more.

I have rebuilt the carbs recently, so no debris.

I am thinking ignition timing at the mo.

[cactusman]

keep us posted

[abowie]

Do you have the reproduction "Champion" plug caps fitted? These can fail in exactly the way you describe.
Check the resistance of the plug leads. It should be about 5000 ohm if you have resistor plug caps fitted and pretty much zero if you don't.

[Hugo]

What happens BEFORE you get to 1800 rpm? Does it rev freely and then suddenly start spluttering once you hit that speed? Or does it struggle all the way to get up there? What does it pull like at, say, 1500 rpm? What happens when you change up? Does it start running evenly again? What happens when you change down? Does it decelerate and you have to wait for the revs to drop back to 1800 before it will start pulling again?
I doubt that timing could account for it. If it's that retarded it will boil and start burning exhaust valves out. If it's advanced it will be burning holes in the piston - pinking and kicking back on starting so badly it would be undriveable.
What colour are the plugs? And are they all they same colour?
My mother told me to never answer a question with a question. Looks like I didn't heed her advice ;)

[cactusman]

Minor point Andrew but when the caps fail the resistance is not zero but much more than 5000 ohms...anything up to open circuit or many millions of ohms..

[chrisfell]

Two things that could cause these symptoms, ignition timing massively out, cam timing massively out.
Whether it is either of these can be easily checked before the engine is next fired up.
However, given that one of the activities done recently was to rebuild the carbs, I'd start there.

My advice would be not to start the engine again until the cause had been found.

[Hugo]

"Car starts on the button and ticks over smoothly." I think that pretty much rules out any timing issues. In any case, if the valves were that far out they'd have hit something by now, and if the ign were out enough to cause it to refuse to go over 40mph in top (which I presume is the kind of speed you're talking about?) it just wouldn't run at all. It would either kick back when you tried to start it, or it would boil up and start eating exhaust valves.
It's that first phrase that's bugging me.
The only thing it sounds vaguely like is if there's water in the carbs. At light loads this will stay at the bottom where it belongs, but when you start drawing more fuel, the water will get sucked up the jet tube where it will get in the way, since the surface tension of the water will prevent its atomisation.
As the owner (sorry can't remember who!) has been working on the carbs, I would certainly pull the float lids & dashpots off & bung an air line down there.
While you're at it, make sure the pistons are free to rise all the way, and more importantly, that they drop with a distinct metallic 'clunk'.
Try leaving the damper rods out of the carbs when you drive it, on the off chance that they are holding the pistons down.
Incidentally, somebody mentioned open-circuit and ohms & stuff at the plug caps. Many people seem to think you need good connections on the HT system. You don't - the spark will jump a half-inch gap in atmospheric pressure. How many ohms is that? It easily will fight its way through any resistance it may encounter along the way.

[Series1 Stu]

I don't think this problem is electrical as the engine would cough and splutter but would probably rev past 1800rpm ok. Unless there's a rev limiter built into the rotor arm and that's gone duff. I don't think that is very likely.

I would look at the fuel delivery first, especially as you say that the pump might be weak. Start by checking it will deliver it's rated quantity of fuel by disconnecting the fuel line from the rail and running the pump for a minute. Measure the fuel you've collected and that should give you a good indication as to whether it is supplying enough fuel. From what you've said it could be that you're​ only getting around 30% of what the pump should be capable of.

If that's all good then check the carbs are assembled to manual specs and functioning properly.

Cheers

[abowie]

Minor point Andrew but when the caps fail the resistance is not zero but much more than 5000 ohms...anything up to open circuit or many millions of ohms..

Sorry if my post wasn't clearly worded

..and pretty much zero if you don't (have resistor caps fitted).

[Hugo]

From what you've said it could be that you're​ only getting around 30% of what the pump should be capable of.

If the pump is only working at 30% it should run perfectly! If this car won't go above 40 mph (which is my estimate) it is only kicking out about 20 bhp (another of my estimates!).
The absolute maximum an E Type can draw is about 1 gallon every 6 minutes, and the pump has to exceed that by a comfortable margin. One third of that will propel you at a decent rate - in fact I doubt you'd even notice anything wrong.

[ETTony]

A quick reply before I get under the car.
Plug caps, rubber ones
Before 1800 it revs freely, then starts backfire and stutter.
Change up, revs drop, accelerate up to 1800 in next gear. I can roll along at 45mpg with the rest of the traffic in top. When I change up it pulls fine up to 1800.
Change down the revs do increase over 2000 and it will roll on light throttle, I do not want to get agressive with the gas till I know the cause.
Plug tips are grey, black carbon on the plug body, dry. All the same.
Carbs. Piston dampers drop freely. The suction across the 3 carbs is even. 12 on my synchrometer.
Fuel. I have had the tank out and lines are new. Will check for water in the float chambers. No water showing in glass filter.
Distributor, it was rebuilt with bearings etc by the Distrib Dr recently. I will check the vac advance metal tube from the carbs to ensure its clear.
Thanks team for your ideas
To add some spice, the timing marker on the damper and pointer are 90deg apart, seems a common prob.

[Heuer]

Run the car without the plenum/air filter and see if that makes a difference. Could be insufficient intake air?

[Series1 Stu]

If the pump is only working at 30% it should run perfectly! If this car won't go above 40 mph (which is my estimate) it is only kicking out about 20 bhp (another of my estimates!).
The absolute maximum an E Type can draw is about 1 gallon every 6 minutes, and the pump has to exceed that by a comfortable margin. One third of that will propel you at a decent rate - in fact I doubt you'd even notice anything wrong.

I'd be interested to know what you base your estimates on.

The standard 3.8 fuel pump was notorious for undersupply issues at the higher end of the rev range. Given that, a defective fuel pump could certainly cause the problem seen. Whether it's running at 30% or 10% is academic. Jaguar weren't renowned for generously over specifying components.

Tony, if I remember correctly the jaguar service manual should quote the fuel pump rating. Unfortunately, I don't have the 4.2 book to hand. I have it on CD somewhere.

Regards

[Hugo]

Distributor, it was rebuilt with bearings etc by the Distrib Dr recently.

Brainwave - I once came across a car that had a weird fault similar to this - it would hunt like crazy; one of the little wires inside the distributor (to the condenser) was earthing out when the centrifugal advance pulled the base plate round.
That's got to be too easy, hasn't it?
You said the piston dampers drop freely - I presume you meant the pistons? I would take the dampers right out & try it.