Engine not revving. Now running fine

[ETTony]

Getting there slowly.
Went thro the carbs again, needles fine.
Slacked Distr clamp, advanced (clockwise) distr and engine speed increased, back off until engine note changed, out for a run around the block, now reving up to 2500rpm. Not much backfire at that point, just no more revs. Adj carb slow run screw for tickover.
Carried out Hugos lawnmower spark plug check. Checked each plug HT lead and saw nice regular sparks up to 2500. No change in spark at the point engine refused to rev further.
I did note that the glass fuel filter is always completely full.
Oh and I had the wires to the coil wrong, changed to w/b to +ve and thick w to -ve, altho it did not appear to affect anything ?
looks like ignition as most of you were saying.
I need to very very accurately mark TDC

Rain stopped test flights

[44DHR]

You said the glass fuel filter is completely full.
This means nothing unless you remove the filter and check that it is completely clear by blowing through it, or temporarily removing it while testing the system.
The fuel flows from the inside of the fuel filter to the outside in the glass bowl mounted in the engine compartment, therefore when blocked the glass bowl will still be clear with a very limited fuel flow to the carbs. We have covered this issue several times before when discussing engines "topping out" at speed due fuel starvation. Particularly an issue on cars that have been sat around for some time or when a car "new" to it's owner has an unknown history to it's fuel filter.
Can you confirm that you have removed the filter and checked it is clear ?
Regards,
Dave

[Hugo]

Getting there slowly.

Oh and I had the wires to the coil wrong, changed to w/b to +ve and thick w to -ve, altho it did not appear to affect anything ?
looks like ignition as most of you were saying.

Normally, white goes to the + and black/white goes from the neg to the distributor. If you have reversed the polarity on a pos earth car, white will go to 'CB' and black/white will go to 'SW' (which is of course the wrong way round.
Coils will work either way, but you may get poor starting if they're wrong.

[Hugo]

Oh, and it's beginning to look less like ignition in my view. Try pulling each plug lead in turn & see if the reduction in performance is uniform.
And what does it rev to when not under load? If it revs freely then I'd suspect fuel starvation. If it won't rev, there is something else going on.

[ETTony]

Thanks again for your input guys, it is all most welcome.
Glass fuel filter, i removed the element when I checked it earlier, at the mo glass bowl is MT, new element arriving tomorrow. Earlier I had the fuel pump apart and pulled the suction pipe from the tank, all clear.
My car is a neg earth, the brilliant XKsUnlimited wiring diagrams show coil as CB+ to wb the distr. SW- to w fuses.
New fuel p/p arriving tomorrow, I will fit it
The TDC mark that I had been faithfully using was some 15deg retarded from my measured TDC (garden cane, steel rule and magnets) ignition timing reset.
Fires up, Revs freely up to a point, then hesitation. Stopped to think and confer.
Yes Hugo, it could well be the fuel pump being a triffle tired, it has been changed at some point as its a SU AZX1300 pump, which I believe is an upgrade on the original.

Way back in the roaring 70's, I had a cracking series 1 1/2, roadster, carmen red, mmmm.
About the only breakdown I had withit was the fuel pump
Maybe its me.

[Hugo]

That coil wiring is wrong. CB pos goes to the distributor and SW neg is from the ign switch in the ORIGINAL pos earth configuration. If you are running one of those old coils on a neg earth configuration, CB is still pos but is now the feed from the switch, and SW is still neg but now goes to the distibutor. Why they didn't just mark them + and - I do not know.

[ETTony]

Thanks Hugo, I have put the coil wires back, the correct way.

[ETTony]

Rechecked my TDC mark and ignition timing.
Fitted new SU fuel pump, seems better, it quickly primed.
Fired up on the button, revved thro to 2500 only then stutter, no loud backfire, just a pop.
A very slight overrun on stopping.
No improvement really.
I decided to look at the cam positions. Crank at my measured TDC

Exhaust cam, slightly out, is this relevant ?
Inlet, pretty damn fine I would say




Q. Do the cams rotate in the same direction as the crank, looks like it ?
I see the posts re needles, worth a go. Could refit my filters ?

I never did the check with one plug disconnected at a time. Tomorrow maybe. Need to clean up my cam cover faces.
OK so we did not crack it today but eliminated the fuel pump and gross cam error.

Thanks again team

[Heuer]

Running without filters will make the engine run lean. Ideally you need UE needles which are richer. Worth a try putting the air filter back on before going any further with needle choice. I assume that with WOT you can see the butterflies are horizontal and the pistons have risen fully up?

[mgcjag]

Hi Tony.....re the cam timing....with the crank at tdc the 2 cam should also be centered.........not to detract too far from your running problem but you cant just assume that with the crank pully at the tdc mark that it is actually tdc...suggest that at some point you set it accuratly.......take for example piston 6 (front) you need to remove the spark plug and set up a dial guage on the piston....if you turn the crankshaft when the piston is on its compression stroke the piston rises, gets to the top and stops, you continue turning and it starts to move down......tdc is half way between when it stops and when it starts moveing again...........adjust the pointer on the sump to the tdc mark and adjust the camshaft sprockets so the cams are central..........you will need to read up a bit befor you do this so you fully understand what you are doing....its quite easy really...pm me if you need to talk it through... Steve

[ETTony]

Steve, I have been around the block with the crank markings.
Firstly I have one of these that has the (original?) crank damper TDC marksup at 3o'clock and the pointer at 6 o'clock.
Secondly a PO had marked the damper at the 6 o'clock, but his marks were 15deg retarded.
Yesterday I measured and noted the correct TDC mark at the 6 o'clock pointer.
Today i received a pointer for an XJ6 which i fitted at the 3o'clock position , which agrees with my measured TDC.
So after all that I have a timing mark that is correct and I can read without crawling under the car. A long journey.

[ETTony]

Yes I will refit my air filters.
I was leaving them off in case I needed to run thro my carbs again.
Lets plan for success.

[abowie]

Have you got an air leak somewhere in the inlet manifold?

[mgcjag]

Hi Tony....it dosnt matter where the marks and pointers are.....what is important is that both cams are alligned with the halfway point between the piston stopping and starting to move at the top of its compression stroke and you have a mark to show where this position is......you asked the question about the cams lining up....

[Hugo]

Have you got an air leak somewhere in the inlet manifold?

Makes sense - except that it idles perfectly! I suspect an air leak, but what could cause it to go haywire at a specific speed?

[Hugo]

[quote="Heuer"]Running without filters will make the engine run lean.

When it is passing a high volume of air, yes, but at less than half engine speed I can't see that it will make a material difference.
There is something majorly wrong here; nibbling away at the edges won't provide a solution.
I realise all I am doing is putting a downer on other people's ideas, and I apologise for that, but I'm playing devil's advocate.

[Hugo]

Yes I will refit my air filters.
I was leaving them off in case I needed to run thro my carbs again.
Lets plan for success.

I don't suppose there's any way you can post a video of what is happening?

[44DHR]

Tony,
Just to clarify, did you check the old petrol filter that you removed from the engine bulkhead glass bowl to see if it was blocked internally ?
Also to confirm that during this latest series of tests that you now either are running the glass bowl temporarily without a filter, or that you now have a new filter fitted to remove this potential restriction on the fuel supply which could have contributed previously to fuel starvation at a certain point on the engine speed ?
Regards,
Dave

[abowie]

Have you got an air leak somewhere in the inlet manifold?

Makes sense - except that it idles perfectly! I suspect an air leak, but what could cause it to go haywire at a specific speed?

Just guessing, but, if you have an air leak, you might still have been able set the mixtures etc up with it present and get it to idle. If then at some point as you increase revs and fuel demand it might be leaning the mixture off.

Does it run any better with the choke on? I haven't read back through the whole thread, but have you tried removing the brake vacuum pipe and blocking it off and seeing if that makes any difference?

[Hugo]

That's a good idea (blanking off the vacuum pipe). I think I suggested the choke several posts back. Another thing that might be worth a try is get a propane blow torch, open the valve but DON'T ignite it (!), and play the gas all around the inlet manifold with the engine idling - everywhere you can get to except into the air intake or carb mouths. If it's drawing in air from anywhere, with a bit of luck it will find the propane which should give a noticeable increase in idle speed.