3.5 running issue - won't rev up or run cleanly, weak spark?

[Lewis]

Hi everyone,

Struggling really badly with this P6 at the moment. Firstly the fuel tank was filled with crud which promptly got sucked up and jammed everything solid, and now this...

Previously it would run and drive fine with a good bit of power and would easily light up the tires, and run through the rev range nicely.

At that point the condensor died - and it would run intermittently. Now I have replaced that, the car will (just) start and run - but it is very down on power and won't rev cleanly or freely and sounds odd too. If you can get it over 3000rpm it becomes very unhappy and will backfire when coming off the throttle. I have a very unenthusiastic looking orange spark, even when taken right off the coil.

It idles OK at the moment but that's about it...

I have replaced all the ignition consumables (NGK plugs, Champion leads, new condensor, points, cap, rotor, LT lead) and have a new coil on order - but have tried two other spare coils. I set the points gap to the 0.015in as spec'd from the factory but have taken that no further.

I did take the carbs off and apart but have sync'd the butterflies, reset the needles and floats and that seems OK (at the time one bank was very rich, the other lean - so felt obliged to) - at least, it should run OK. I put a pair of new needles in as well as the old two were mismatched (!).

I have looked at the dizzy and well, barring it all potentially being set up wrong, the little copper earth lead from the points to ground looks very frail and tatty - could that cause it?

The rev counter seems fairly steady but does occasionally flit up and down a few hundred RPM, out of time with the engine.

So, do I just need a good tune up or is there something else amiss here? Getting very frustrated, and tired, of this as I got screwed on the insurance so it is my daily (non) driver.....

Thanks for any guidance here

[Tricky]

What carbs you running? could be a carb problem

[Lewis]

They're HIF6s, probably all over the place too All a bit of a non-starter this, really - but I'm just going around in circles now doing the same old things.

I did follow the Burlen guide to reset them to factory 'tuning' settings so it should run OK, especially as you can only set the idle mix - both have fuel and are set up in similar positions, both dashpots move freely too.

I may nurse it down to my local independant and get them to look at it soon but I just thought I'd canvas for opinions here in case I've missed, or incorrectly set, something

[Tricky]

Remove the dash pots and check that the pistons aren't sticking also have a look at the needles and seats they should all be sitting at the same level to start with, also check the carb breathers and don't block them off.
Also check the dwell angle which should be 51-62 degrees

[kiwicar]

My first suspect would be the coil, a condenser dying can take the coil down with it. next I would look at that earth lead on the points, make sure it isnt shorting by a bit of frayed connector to somthing it shouldn't when the advance come in. Next what sort of state is the distributor in? is the shaft sloppy in the bearings, because you can get "progression on the shaft if it is warn and at high revs it causes so much scatter that it is a wonder it fires at all. I would look at getting a nice regular blue spark before doing anything more to the fuel side, when you doo look at fuel my first bet would be crud in the fuel line, then blocked main jets then air leaks.
Be worth a check that the pistons rise together on the carbs, sticking a different profile needle in a pair of carbs can be done to get over a sticky spot on the traval on the piston.
Mike

[Lewis]

That earth lead in the dizzy is supposed to have a sheath? Mine's just a tatty bit of copper wire, about 12 strands if that

Thanks for all the tips so far.

One thing that confuses me - the needles run in the jets which you can move up and down with the adjustment screw - but the jets themselves seem to sit in sleeves as well. These sleeves, on my HIFs, are about 2mm below the level of the bridge on the carbs - so when you have the needles set about the 'correct' starting point of two and a bit turns down they are level with the sleeves, below the bridge.

Is that right? Bit of a cock-eyed description there but I'm sure you'll know what I mean.....

[Richard P6]

Have you put a volt meter on the positive side of the coil?

Just a thought but you have a ballast resistor in the wiring loom and these can sometimes fail.

I had a similar problem which was caused by my predecessor wiring the coil by using a scotch block onto a wire which was scotchblocked onto another wire and then onto the original coil wire from the fuse box.

Replaced that and the problem went away

[kiwicar]

The su carbs have 3 positions for the needle in the piston, make sure you have them in the right one, it effects where you set the jet at idle, which in turn effects the transitions on the needle at higher revs (on some needles it effects the way the mixture richens when the piston tops out in the carb)
Mike

[ian.stewart]

Weak spark,
What type of coil do yuo have? there are generally 2 types, one for Ballasted resistor and one for no resistor, the first is 7-8v coil and the other is 12v coil, fit a 12 v coil in a ballasted system and you will get a weak spark, as its only fed 7-8v, its also possible the ballast bypass has been left out for cranking, which feeds 12v to the coil while the engine is cranking over.
another possibility is the coil is wired around the wrong way, this will allow the coil to work, but again with a weak spark.

[Lewis]

Running a ballasted coil, 1.5ohm jobby. Is wired the same way, I think, as the one I removed.

All the coils I have slosh a bit, that right?

Some pics:









Tried taking the LT lead directly to the coil - no difference....

Mullered screw heads are nothing to do with me! Must put some oil on that wiper too....

[harvey]

.
Also check the dwell angle which should be 51-62 degrees

Dwell angle should be 26-28 degrees, and the points should always be set up by the dwell, and not by the gap, 15thou is just a starting point to get it running to make setting the dwell easier.

[harvey]

(at the time one bank was very rich, the other lean - so felt obliged to)

If one bank is lean, and the other is rich, that isn't the way the carbs are set up on the manifold, the NS carb supplies numbers 1,4,6 & 7, the OS does 2,3,5 & 8 so neither carb is supplying a complete bank.

[harvey]

Did the new points have a pointed locating peg on the bottom, and if so did you locate it correctly in the arm coming from the vac unit? Conversly, did you fit points without the peg, when you should have fitted the ones with the peg on them?

Looking at your pics you can see that the arm from the vac unit is in a different place to where it was before you fitted the points so it's possible that you have missed the locating hole. See if the baseplate is moving around all over the place.

[Lewis]

Looking at your pics you can see that the arm from the vac unit is in a different place to where it was before you fitted the points so it's possible that you have missed the locating hole. See if the baseplate is moving around all over the place.

Aha! I did indeed fit one with a peg, which located into a hole on the baseplate in the distributor - but I didn't notice that there might be something else underneath.

I shall investigate in due course.

Nice to know about the carbs feeding the relevant cylinders too - just occured to me that at the time I only checked one plug from each bank so just assumed.....incorrectly! Makes sense as to why the plugs were hit and miss in "random" cylinders when I took out the old set after running it a bit more.

Great advice people!

[Lewis]

Checked the vacuum advance pin - not that - and if I blow or suck down the tube I can see the baseplate moving so assume that' all OK....