Engine cut out and backfire

[James k]

Hi,
I've been driving my Traveller a lot for the past few days after getting it back from ESM (It needed quite a bit of work, both trunnions, brakes, rear suspension and a few other things). It's been running fine (apart from lacking a bit of power uphill, I'm thinking of playing with the timing) and I haven't had any problems with it until just now. I started it from cold and drove it down the road to the shops. As I was coming out of the car park on my way back, after leaving it for ten minutes or so, the engine started juddering and running erratically and then cut out. I started it again and it was still sounding strange. I revved it quite a lot and it then backfired loudly and shot out some grey smoke and then went back to normal. I drove it home with no problems and sat with it idling in the drive for a few minutes. What might this have been? As I said, it hasn't done anything like it before and it ran fine afterwards.

I wondered if it could have been that it wasn't warmed up properly. I usually sit warming it up for about a minute when it's cold but this time I set off pretty much straight away. Could this have anything to do with it?

Thanks
James

[bmcecosse]

Maybe a sticking valve...

[James k]

What could cause that and how would I check? I've done the clearances and all the valves seemed to be working fine. Would that explain it backfiring and then immediately returning to normal? It felt like the engine sneezed and was then fine!

Thanks

[i lovemylcv]

Sometimes this happens when the Carb main jet is stuck open caused by Choke failing to close, check this is working correct

[kennatt]

If its now running OK just leave it,wait till it start to playup,if might never do it again,No point in fixing something that not broken.

[mike.perry]

Check the distributor clamp is tight and the distributor is not rotating

[bmcecosse]

Maybe it was just ice in the carb.

[James k]

I drove it around a lot yesterday and yet it warm up before I pulled off each time. It drove fine and didn't do it again. BMC, does ice form more readily in the carb than elsewhere? It didn't seem cold enough for ice here yesterday.

[MikeNash]

James k,

Carb icing is a rare and rather baffling phenomena but I think its unlikely to be your problem. Note however, it doesn't need very cold weather for it mostly occurs ABOVE freezing and requires a medium to high humidity (which doesn't happen much below freezing); see this chart http://www.atsb.gov.au/media/47763/carb_icing.pdf Also it tends to stop engines with SU carb by over-richness, at lease it did on my old 803cc ex-post-office van which is the only Moggie on which I've had it - usually just after a cold start in foggy weather that's just above freezing.

Your backfire suggests to me a temporary weak mixture. Put your finger under the SU piston and after raising it, check that it drops smoothly and fully. And let us know how you get on!

Regards, MikeN.

[bmcecosse]

As Mike describes - ice forms very easily in the choke section of the SU carb - weather slightly above freezing, cool under bonnet temperature and moisture in the air... It can form a plug which indeed causes poor running (indeed possibly rich - with unburned fuel collecting in the exhaust..) - and then may suddenly clear (and fuel igniting - which is what a 'backfire' is) as it is perhaps sucked into the engine! Hard to see what else (besides sticking valve and the ice) could clear itself and then run perfectly well.....

[panky]

I had this on one of my campers, turned out to be a loose LT lead on the coil. As described by BMC unburned fuel passed into the hot exhaust and - BANG.

[chesney]

You can cause a 'misfire' by switching off the ignition while running in gear, then switching it on again 3/4 seconds later. Not that I ever do it ;)
So could well be as Panky suggests.

[kennatt]

As said.if its ok now don't fret about it,these things just sometimes happen,if you don't know how,fiddling with the carb could make things worse.Just enjoy.

[bmcecosse]

Turn the air intake tube down to the exhaust for winter - if it's not there already.

[James k]

I've driven it today and it's been doing it again :/ It hasn't backfired but the engine has been occasionally juddering and kangarooing. It suddenly starts jerking along (almost as if you were pushing the clutch up and down quickly) and losing power so it has to be really revved to keep going. Then it will be fine for a while, as it was all day yesterday.

I've checked the carb piston and it's fine. The air cleaner wasn't in the correct position but it is now. It's pointing directly over the exhaust pipe, is this correct? The low tension leads to the coil are worn looking but there's no actual break in the wire so I assume they're not the problem. Could it be a problem with the fuel pump?

Thanks
James

[bmcecosse]

Most likely the condenser.... Is it still doing it after turning the intake ??

[James k]

I've not driven it since moving the air intake. Is it likely that that could cause such a big problem? Does a faulty condenser typically cause engine jerking like that? I have changed the condenser recently but I suppose it can be faulty. I've still got the old one so I'll try putting that back in tomorrow. I'll be extremely happy if it does turn out to just be the condenser. I've basically sunk all the money I can into it so far.

Thanks

[bmcecosse]

No - the condenser never causes any symptoms like that - that's why I suggested it..... geeeezzzz.

[kennatt]

[James k]

Yeah yeah, alright bmc . I meant is it the overwhelming probability that the condenser has gone or one of many possibilities? I'll have a look soon and report back. The annoying things is that it's only doing it intermittently. If it was constant then it would be easier to diagnose. I.e. It's difficult to know if I've fixed it or if it's just taking a break from playing up.