Carburettor Help!!!

[222s]

Can anyone tell me how the needles in SU HS6 carbs are supposed to come out? I've undone the grub screw holding it into the piston but the fugging thing won't budge.... If it's just a case of using a pair of pliers (& therefore destroying the needles), then fair enough but I'd rather avoid that as I might want to refit them. Intending to try out the next needle up to see if that cures a full throttle pinking that only appears at certain (unknown as I don't have a tacho) revs at motorway speeds.

Fankoo

[Pigeon]

Unless I've remembered totally wrong then indeed all you should need to do is unscrew the grub screw. And they do stick a bit. Try popping the piston in the oven and cooking it up too 200 deg C and seeing if differential expansion helps you get it out.

[austingipsy]

A model makers vice with plastic or rubber jaws is perfect for gripping without any damage to the needle.

[barney paull-edwards]

yes they stick but I suggest your problem is not them. If the problem started gradually it is more likely to be ignition wear on points heel or timing. Why should needles need replacing unless you have changed something in a re-build?

[222s]

Originally Posted by barney paull-edwards

yes they stick but I suggest your problem is not them. If the problem started gradually it is more likely to be ignition wear on points heel or timing. Why should needles need replacing unless you have changed something in a re-build?

I recently swapped the needles down & the ones I want to fit are the old ones - also not points as have electronic ignition. Nor is it a gradual issue either, as I've just been resetting the carbs from an seriously out of balance setup that ran ok but drank fuel, and am now fine tuning them. The idea behind the needle swap was to see if that eliminated the problem.

The pinking itself is weird as it sometimes appears after some fill-ups (so also been wondering if it's poor fuel) but isn't present at high gear / low speed throttle situations (ie 4th at 25mph & foot flat on the floor, it just pulls happily). The normal situation is full throttle situations at higher speeds but provided I back off a touch, then it goes (& there's still enough power to reach quite naughty speeds on the motorway).

It's the intermittent nature that is really annoying me. Also being in central London, there isn't a nice derestricted road nearby where I can check whether I've eliminated it.... However if it's not a mixture issue, what else is likely? Could it be something like dodgy plug leads?

[barney paull-edwards]

Sorry but did know you had GOOD working knowledge of system! It is just possible that you have a set of carbs with "floating " needles to self align, either way other advice on oven is best.Have you got the correct advance curve in your dizzy? Huge variations in fuel quality at the moment, witness recent trouble with silicon in fuel, Volvo`s will run on anything due to compression ratio but your random pinking points to fuel.

[BillKat]

Wonder if it might be an air leak, intake side, aside from the needle thing. Squirting carb cleaner or WD round the intake areas often shows it, as a change in engine note. Dunno if you've got the plastic air filter housing, mine had twisted & warped with heat & age (know how they feel LOL) and weren't sealing to the carb.
Sounds like doing a plug chop is going to be quite hard in c.London ..

[austingipsy]

You could try some of that new BP 102 octane juice if it's at the pumps yet, that should keep you right.

[amazondean]

If the car is pinking the timing is too far advanced. You can spend a fortune on tuning but it all boils down to pinking. If it pinks, retard the ignition until it stops. It's as simple as that.

[Pigeon]

Originally Posted by 222s

The pinking itself is weird as it sometimes appears after some fill-ups (so also been wondering if it's poor fuel) but isn't present at high gear / low speed throttle situations (ie 4th at 25mph & foot flat on the floor, it just pulls happily). The normal situation is full throttle situations at higher speeds but provided I back off a touch, then it goes (& there's still enough power to reach quite naughty speeds on the motorway).

I wonder if your advance mechanism is sticking or something? Check the vacuum capsule and the bobweight mechanism and make sure it's all moving freely... I'm wondering if something is getting stuck and giving you too much advance and the momentary change in conditions when you back off and reapply shakes it free or something like that.