Carburettor Help!!!

[222s]

Originally Posted by 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.

No need to apologise - I should have been clearer with what I wrote! Also, wouldn't go as far as describing my knowledge on this as good - I only first worked on carbs properly over the last few months but a combination of advice on here & in person from Harvey (wellshj) has taught me a lot

Haven't touched the dizzy. However your comment about fuel quality echoes my own concern, as often around town it's fine until I fill up....

Over the weekend, on a long run I tweaked the mixture by 1/2 a flat richer on a couple of occasions (based on the assumption that the mixture might be a bit lean) & it didn't make much difference to the running.

Originally Posted by 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 ..

Mine has the separate filters. Is the seal between these & the carb body important as well? I will also check the carb to manifolds & also the spindles. There is a slight issue with the idle being a little bit high sometimes then dropping back to normal - could this be due to an air leak?

Originally Posted by austingipsy

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

Tempting but I dread to think the price! I'm using normal (97?) at the moment & it's been happily running on that for about the last 10 years. However I'm off up to the Retro Rides show this weekend, so if I haven't had time to sort out anything else, I'll feed it some higher octane juice to see what difference that makes.

Originally Posted by Pigeon

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.

Mmmm - that had never occurred to me! Will certainly check the innards of the dizzy. If it's sticking, it's not freeing off instantly as what I meant by backing off was going to say 3/4 throttle rather than just lifting then reapplying.

Which reminds me - when I just boot it & don't lift off, the pinking seems to clear (or is drowned out by the noise of the engine - not sure which....) & it pulls smoothly to about 65 in 3rd & 80 in 4th (4.55:1 diff) but when I engage the overdrive & reapply full throttle, the pinking is back. Your comment about the advance makes a lot of sense, as it could easily explain why it seems to be at a certain spot in the rev range (abeit only under full throttle in the higher gears - I can't seem to replicate it in 1st or 2nd gears).

If the dizzy & plug leads are ok, & there are no air leaks, could too lean a needle produce this pinking issue at a particular spot in the rev range?

Thanks again to all

[BillKat]

The idle being sometimes high, when you come off the pedal, could be a bit of air. Mine used to do that because of hanging up in the bore due to filth, though sounds like yours have had a sort-out recently maybe.

Re leaks, if an air gap/leak happened after the carbs were set up, it would upset the running at some or several points 'cos of the extra un-jetted-for air. So yup any unaccounted for air (gap/leak/filter removed etc etc) isn't wanted.

Not sure what the overdrive/pinking bit indicates: perhaps the basic timing is very slightly out. Although I thought there would also be pinking at low speed/high load in that case, but there isn't. When I've had pinking it's been at lowish revs/high load, haven't had pinking at high revs but not low revs, p'raps the panel has some thoughts on whether basic timing can cause that.

[222s]

All sorted now!!!

Many thanks to all for advice etc. It's now running & performing how it used to, so I'm a happy chap! The dissy advance seemed a bit sticky, so I lubricated that with plenty of 3in1 oil & also checked the manifold nuts (a few were a bit loose). Neither of which I would have thought of without the advice from you guys

[222s]

The pinking is back although but not as bad as before. Definately intermittant & just at a particular point in the rev vs load range.

I'm going to replace plugs, leads, dizzy cap etc (these could do with replacing anyway) in case the problem is partly electrical, & then go from there.

[Derek UK]

Do you use the same fuel from the same place all the time or just go in anywhere? You might just have bought a bad tankful. Fuel doesn't stay "fresh" for long and half a tank left for a week might just lose enough to trigger the pinking again. I think I'd try another degree or two of retarding. Make sure the locking bolt is tight.

[222s]

I'm pretty sure its more than just fuel (although that may be part of the problem), as it had begun pinking on regular unleaded, and filling up with the high octane juice made little, if any difference. I'm going to sort out the ignition system anyway as it hasn't been done for a while & that's by far the easiest way to eliminate that line of enquiry.

I've never used a timing light so is there another, idiot-proof way to retard the timing, like a knurled adjuster on the dissy (I vaguely recall that a previous BMC car of mine had something like that) & if so, how is that calibrated?

Thanks!

[austingipsy]

Just thinking maybe you should try the cooler running spark plugs. Amazon sell them as sport and standard, you want sport, ngk. Also, if you had a weak return spring on the cetrifugal advance weights when you cleaned/oiled the mechanism you might have aggravated the situation.
More noticable after a fill up is probably down to the extra weight you are carrying. And more noticable on motorways might be down to the added effects of wind resistance, not really an issue below 50mph so high gear lower speed wouldn't induce the same effect.
My landrover and gipsy had those wee advance/retard knurled knobs on the side, very handy.

[amazondean]

Don't mess about with timing lights. The timing is probably already too far retarded as it is, using one of those. Loosen the pinch bolt and turn the dissy anti clock (retarding) a fraction and retighten then try up the road. Keep doing it. The pinking will finally disappear!!

[222s]

I'll tweak the timing a bit & see what difference it makes


Thanks everyone!