Engine: 2.1 Carb B21A: Backfiring Redblock - Help Please

[MissDMeanor]

I'm having a nightmare with Mildred my '76 240 - she's jealous of Mouthy's problems so now I have two undriveable Volvos

Ok, a friend of mine fiddled with Mildred's screws a couple of months ago to help her tick over a bit better. First off she was juicy so he adjusted it again.

Then it was a slight hiccough or misfire every now and then but now this has progressed so that I cannot drive her 20 yards without her backfiring.

I'd just moved into a new house and was hoping to impress the neighbours with how quiet the dogs & I are, and what lovely cars I've got when Mildred blew her back box apart on the way over Turned up at 5am making a bloomin' racket - well, I've arrived lol.

Anyway, she had her MOT last week and supposedly they were going to sort the mixture out at the same time as that & fitting a new back box. (£120 for back box, front brake pipe and MOT.)

Driving her the mile home wasn't too bad but I went to take her shopping yesterday and turned round and came back after 100 yards. She's exactly the same, backfiring, misfiring and just generally acting her age....

Can anybody help please - what is it? Is it damp caused by the flooding a couple of months ago (when she magnificently sailed through some very deep water) or is it the mixture? And why has it got progressively worse?

Many thanks

[IC]

Originally Posted by MissDMeanor

I'm having a nightmare with Mildred my '76 240 - she's jealous of Mouthy's problems so now I have two undriveable Volvos

Ok, a friend of mine fiddled with Mildred's screws a couple of months ago to help her tick over a bit better. First off she was juicy so he adjusted it again.

Then it was a slight hiccough or misfire every now and then but now this has progressed so that I cannot drive her 20 yards without her backfiring.

I'd just moved into a new house and was hoping to impress the neighbours with how quiet the dogs & I are, and what lovely cars I've got when Mildred blew her back box apart on the way over Turned up at 5am making a bloomin' racket - well, I've arrived lol.

Anyway, she had her MOT last week and supposedly they were going to sort the mixture out at the same time as that & fitting a new back box. (£120 for back box, front brake pipe and MOT.)

Driving her the mile home wasn't too bad but I went to take her shopping yesterday and turned round and came back after 100 yards. She's exactly the same, backfiring, misfiring and just generally acting her age....

Can anybody help please - what is it? Is it damp caused by the flooding a couple of months ago (when she magnificently sailed through some very deep water) or is it the mixture? And why has it got progressively worse?

Many thanks

Julie, have a look at the points, if they are black/bluish it may be a faulty condenser.

[Paul Clifton]

I agree with IC, change the points and condensor and have the ignition timing checked.

Paul.

[Velorum]

Weak mixture?

All my backfiring problems have been due to this in past cars.......

[Pedro Fandango]

the points, condensor, HT leads, plugs & an oil change were done about 2 monthes ago on her

[IC]

It's worth looking at the points to see what state they're in even though they were recently changed.....

[morsing]

When exactly does it back fire? Idle, accelerating, cruising, coasting etc...

Did the back-firing actually blow the back box? That could have only been un-burned fuel in the exhaust I would have thought. Normally too lean mixture shoots out the carb, too rich out the exhaust. But it sounds like the timing might be a problem.

If the distributor weights are stuck it can cause back firing... Maybe worth checking?

P.S. When's the house warming?

[MissDMeanor]

Originally Posted by IC

It's worth looking at the points to see what state they're in even though they were recently changed.....

Thanks IC - Pedro & I serviced her very recently but I will check them anyway.

[MissDMeanor]

Originally Posted by Ian Hutchinson

Weak mixture?

All my backfiring problems have been due to this in past cars.......

Hi Ian. Thanks - this would make sense so it looks as though the garage didn't set the mixture. I'll have to pop back and check with them (they were very impressed with such a golden oldie)

[MissDMeanor]

Originally Posted by morsing

When exactly does it back fire? Idle, accelerating, cruising, coasting etc...

Did the back-firing actually blow the back box? That could have only been un-burned fuel in the exhaust I would have thought. Normally too lean mixture shoots out the carb, too rich out the exhaust. But it sounds like the timing might be a problem.

If the distributor weights are stuck it can cause back firing... Maybe worth checking?

P.S. When's the house warming?

Hi Henrik

House warming? Hopefully when I get the blasted heating sorted lol.

Ok, it feels just like a flatspot on acceleration does. I tend to keep my foot at the top of the gas pedal in Mildred (bless 'er) and it has loss of power for a few seconds then a very loud bang. It's quite exciting really and has created great amusements (I hope) amongst my new neighbours.

She was/is booked-in back in Shropshire for a cambelt change and timing but unfortunately she'll never make the one and a half hour trip as she is...

Yes, the back-firing blew the back box - it's the loudest and most violent backfiring I've ever heard (it would be)