snap, crackle, pop and bang

[timmyboy]

Hi,

My car has always popped a tiny bit when you take your foot of the gas but never badly. The other day I reset the points and the timing and it was ticking over great and wasn't lumpy when you opened up the throttle. I took it up the road and it was fine, went like the clappers, really smooth for a bit but then it started popping and banging like the end of the world was on it's way. Got it home home and had another fiddle, put it back to what it was before and it was running like sh*t. Now no matter what I do it seems to pop really badly even with the throttle open. Went out to have another go today and it seems even worse than it did before without it being touched. It's coming from the right side, it will pop for a bit the bang really bad in the silencer (the neighbours are loving me). It also seems really lumpy now, which it has never done before, almost like it's not firing on all cylinders. I want to do a compression test to see if it's got a leaky exhaust valve, but my tester isn't long enough to fit in the plug hole. If the timing and the points gap is correct what else could it be? I know this sounds a bit amateur hour but I'm not sure where to go fom here!!
Sorry I'm really going on a bit

[veryporky]

sent you a pm

[impmad2000]

What carbs are you running ?
Is it Zeniths ? Have the small pipes fallen off the outside of the barrels of the carbs ? Used to happen to mine regularly, till I took the idle shut down circuit off (See Gary71's website)
Tim

[Gary71]

As Tim says or maybe the float has stuck on one carb.

My car started popping and banging excessively, even with a open throttle, just before the carb caught fire and melted... so be careful!

[davidppp]

All that good advice, plus idle jets blocked..

These are pesky things..

Kind regards
david

[timmyboy]

They are webers. I think I will probably need to rebuild them before I do anything else. Is this as much of a nightmare as I think it looks! There seems to be some slight leakage here and there but I don't know if that's to be expected.

[davidppp]

No, I'd not just rebuild them.

Chances are good that will not cure it.

Best to diagnose it first if you can..

Take out all the jets, and see if they are clean..

Then check the float levels somehow..

You will need the guage anyway if you rebuild..

Finally get a thorough check of the advance mechanism,,it xcan stick..

Kind regards
David

[Gary71]

I'm with David, sounds like something has changed so you should be able to fix it in situ.

If you do eventually rebuild it's well worth getting the spindles re-bushed or fitted with seals. This really helped my idle quality, and off idle performance.

[chris68]

Just wondered how difficult it is to re-bush the Weber butterfly spindles. I've noticed quite alot of play in mine. Is it something best trustd to a specialist? Any recommedations?

Cheers,
Chris

[Gary71]

I cheated and had seals fitted to my Zeniths. I used http://www.gasure.co.uk/ £50 for both carbs, which I thought bit of a bargain.

When I got them back I put some considerable time into aligning the butterflies on the spindles and the butterflies to each other really accurately so I'd have half a chance of balancing them. Worked a treat

[chris68]

Interesting ... thanks for that.

How did it work? Did you send the carbs to them so they could strip, replace bushes and return the re-assembled carbs? Do they fit new spindles too?

Cheers,
Chris

[Barry]

As has been said: just concentrate on things that could have happened 'overnight' so to speak. Therefore, things blocking up, falling off, shorting out, coming loose etc.

I'm sure you weren't, but avoid introducing new potential problems (re-built carbs etc). At the moment you are in the 'nice(ish) position of having a car that was running very well, so you can only be looking for a fairly narrow set of problems.

Funnily enough, if I hadn't read the above posts, I would be suspecting closed points or failng sparks, rather than fuel.

Might be worth doing a quick (re) dwell test, timing check, and spark strength test: mainly because all of these are quick, clean, free and pretty easy, just to be absolutely certain that you can rule these out; after all bit of a coincidence after these areas have been worked on? Hope you get to the bottom of it O.K.: look foward to an update on how things go

[Gary71]

Like Barry said

I stripped the carbs down to just the lower body with spindles and butterflies in. They removed all the butterflies, did the work and put them back together. They weren't very well lined up, but for £50 I was prepared to spend some time on this myself.

[timmyboy]

Right.......thank you for your comments last time I put up this post, well, unfortunately I seem to be no nearer sorting the problem. Although I do now seem to have worked out it's not firing on all 6 cylinders. This would obviously explain why there is unburnt fuel getting into the manifold. I have replaced the leads, points, distributor cap and rotor arm (to be fair they were all looking a bit tired anyway) but to no avail. I seem to have a problem with no. 6. I've tested the resistance of the coil and it seems to be correct. I have tried looking at the spark from all six cylinders and also straight off the coil and there doesn't apear to be any difference. If I try running it without the lead on no. 6 it seems to make no difference. It doesn't seem to make much difference taking off no. 4 either. But it makes a big difference taking off any of the others. I have had the tops off the carbs and everything seems to be fine. If there were a problem with the carb on that side causing unburnt fuel in the exhaust, surely it would have to be flooding into that cylinder?
I have tried pouring redex down the carbs. When poured down 1, 2, 3 and 5 every time the motor would slow up while it was burning it, 4 didn't make a difference at first but then started to slow up but there was no change with 6. It did stop the banging for a bit, but I can only assume it was lowering the temp of the exhaust therefore stopping it burning there. When I tried it later the banging was back.
I was certain it was something to do with the ignition. When I replaced the leads I fitted them without putting the seals (not sure what they are called) over the distributor cap so I could remove them easily if need be. I started it and it was running fine, went for a run, it seemed fine, wasn't lumpy or popping. When I got back I fitted the seal things and it was running on 5 cylinders again. So this why I replaced the cap and rotor arm.
I apear to be waffling more than on the first post but it really starting to do my in noggin.
To be honest I'm not sure if I'll be able to fix it before my neighbours set fire to it, and possibly my house, in the night.

[Gary71]

Hi Tim,

Keep at it

I'd be tempted to put one of your old HT leads on No.6 again!

Have you tried swapping the plugs? It maybe that the plug on No.6 has broken down so might still give a spark when you hold it against the head, but doesn't work when under pressure.

Is the plug on No.6 wet after it's been running? If so is it wet with oil or fuel? If it's neither then potentially you are not getting fuel to that cylinder. Check the idle and main jets for that cylinder and also that the accelerator pump is working. It may be leaning out.

Is the HT lead shorting to the engine anywhere on route to the plugs?

Have you checked the valve clearances recently? Always worth a look.

Good luck, you will find it soon