Sticking carb needle

[surfergirl]

Hi Folks hope your enjoying the weather.
Developed a missfire on the way home today, same as I had this time last year. Back then it turned out to be the condenser, so i went straight for that, tried four to no avail. Swapped coil ( I know its never the coil!) no joy. Cleaned and gapped points, no good.
So just before giving in, noticed with air cleaner removed the needle wasnt all the way down in the carb dashpot, had a fiddle and got it sliding again and that has got rid of the worst missfire.
Is it dirt in petrol that makes it stick or through air cleaner, should I strip it down and fit a recon kit or leave well alone.
thanks for any advise.

[bmcecosse]

Take the bell off, clean carefully with no more than Tcut and retry. Put a couple of teaspoons engine oil in the top...

[surfergirl]

Thanks,
Cant remember doing anything to the carb for many years, which is a testament to the design.
If it aint broke dont fix it.
Funny how it gave the same missfire as the condenser.

[surfergirl]

Thinking about it, cant see why the needle not dropping all the way would cause a miss fire. Wouldnt it miss at idle, then be fine as the needle lifted?
It feels like your running out of petrol, kangaroos, pops and surges, then loss of all power. You can put your foot flat on the peddle and theres no power, then it recovers.
Still doing it this morning only not quite as bad. Only seems to happen in the summer, vapour locks in the fuel?
Cheers

[bmcecosse]

Clean the carb!!! It MUST be perfectly free to rise and fall....

[surfergirl]

Tried cleaning the carb, fuel pump filter and tested the pump by removing the pipe and switching on, filled a jar with petrol no probs. Still runs rough, So Ive ordered a set of points and condenser from the distributor doc. so will see what happens then.

[bmcecosse]

And then piston now rises and falls smoothly?

[surfergirl]

Yep, goes up and down drops with a slight clonk. Fitted the new points and condenser from distributor doc. so well see how that goes. Supposed to be better made and better quality.

[surfergirl]

mmmm that worked for a while, now its back again today, feels like running out of petrol. So I checked the points in the su pump, which were a bit furry, cleaned them up and went for a quick run. Still the same, feels like fuel starvation rather than a miss fire.
Last two days to the beach and back have been fine, only happened when nearly home. Petrol tank is full, so Im not running on vapour.
Has anyone tried the new pumps from Bull motif, the ad. in Minor Matters says superior alternative to the SU.

[panky]

Try taking the fuel cap off when it happens to see if it pulling a vacuum.

[surfergirl]

Thanks, I will.
If I remove the hose to the carb and it fills a jam jar, that should show the pump is working fine?

[panky]

It depends on how quickly it fills it, if it's a minute or so then it's fine. Have you checked the float valve in the carb, there could be a blockage but try the tank test first.

[bmcecosse]

It should do a pint a minute.

[panky]

Big jam jar

[amgrave]

If you have got a 5 Ltr fuel can it would be better to use that to fill using the pump as advised above, this will not only show if it is working properly but will show a fuel tank vacuum as well.

[surfergirl]

Thanks for the suggestions, Ive got a new pump ordered just in case. Took the float chamber off to see whats going on and it was pretty dirty in there, lots of redish bits from the fuel (rust?) So cleaned it all out, blew into the inlet pipe to see if the float is switching on and off, which it is, but I guess the needle could be sticking so the chamber doesnt fill up every now and again causing the mystery problem.
Sooooo whats wrong with an inline filter between the pump and the carb?

[bmcecosse]

Can cause problems, and no need anyway! The pump has a filter - is it clear?

[surfergirl]

Thanks,
yep cleaned the filter in the pump couple of days ago, wasnt that dirty. What probs does inline filter cause?

[panky]

Fuel vaporisation on a hot day causing fuel starvation

[surfergirl]

Ah, so perhaps best to leave replacing the inline filter thats fitted. Mind you it wasnt hot today and plenty of air moving around (it is Cornwall!)
So cant see it being fuel vapourising, but you live n learn.
Maybe fit new float needle and seat.
Thinking about it, it never happens in winter.