Club 80-90 Forums

Hi, just ready through some of the threads regarding popping/backfiring and a lot of them seem to be air-cooled/carbs.

Just wondering with my 2.1i SS engine, drove for 2 hours, driving very well (fast), was just cruising along.

Then got off the motorway and then noticed a popping sound, very subtle. Played around a little and noticed it ONLY happened when putting my foot down. Lifting off, the popping stopped. It DIDNT seem to effect performance.

I did notice that as I reached my destination, at low revs could hear the popping much more.

Will take it for a drive tomorrow and see if symptoms are still there.

But to take some educated guesses (based on the search function), main one being, air in the exhaust system, igniting the exhaust fumes, backfire! But in this case not on the deceleration. My exhaust is quite old and looks dodgy. Just biding my time to get the full stainless steel, now maybe is the time.

My mixture hasn't been touched in ages, and Ive not had these symptoms until today. So can it suddenly run rich?

any other things I should check.

went for the drive this morning and noticed the following.

Only happens while driving, Ive tried revving it stationary, but can't reproduce it.

happens when its got warm, not at the start

when its in full popping mode, then it happens on acceleration and deceleration.

happens intermittently, sometimes stops for a few seconds then starts again lasting for some minutes

might be more of a knocking noise than popping

I can't see anything obvious coming from the exhaust pipes/joints

As I said before, its still driving very well at the moment.

could be timing, vacuum hoses, is it a backfire or a missfire?

could be a wheel bearing/bearing failing

mark

whats the difference between a misfire and backfire? do they sound different too?

it sounds like a hollow chug, like a tractor. It doesn't start straight after starting the engine, only when pulling away.

When I drive fast its hard to hear, as it is happening so fast/often to the revs of the engine, then it sounds more like a pop.

then when I slow down, decelerate into a junction then u can hear it much slower, like a chug.

But when I'm stationary, I thrape the engine a little, but it doesn't happen.

what can I do when stationary to replicate the sound so I can then be at the back of the bus to get a better idea?

maybe its more of a misfire when under load only.

OK, spoke with the old man (mechanic) and he said it sounded like a misfire. As backfire is bloody loud.

I took all spark plug cables off and then on again, and opened up the dizzy hat. No black residue.

Also tried to shake around the engine a little with my feet.

Went for a drive, and the chugging wasn't there anymore. Gave the engine some wellie and was still fine.

Then turned off onto side road and played around at low speed, in 2nd and 2rdBut decelerating and it came back a little.

Ive just noticed that a bolt at the back of the exhaust, before the end silence, in the middle is loose.

Will tighten that up and give it another go soon.

update: went for another drive, and if I play around and low revs then it comes back. High speeds are better now

I give up for today then

take the plugs out and have a look brown is good white is weak mix black smelling of fuel rich mix, rich mix could be temp 2 sensor failing. then the ecu thinks the engine is cold and increases the fuel and then you get your missfire, i think you should clean all electrical contacts with contact cleaner and a toothbrush takes about 1hr start one side and work your way round the engine bay, clean the earth wire left side of engine contects to the body make sure metal on metal and the brown wires near the earth wire.

it sounds like a loose/dirty connector as it went after your fiddle with the ht leads could be them but you could of knocked/moved anything, good luck with it

mark

mark richards wrote:take the plugs out and have a look brown is good white is weak mix black smelling of fuel rich mix,

All well and good if this is done after a 20 min high speed run over 3000 rpm.
plugs will be sooty if checked shortly after a cold start, or a warmed up idle

have you serviced it recently?
plugs, leads, cap and arm?

not ran since yesterday, light brown color. Should I clean it up a little?

The following is after a little clean to take some deposits off:


All about 18 months old.

HT cables are same age, 1 is only 6 months.

Well that rules that out then.
As you can imagine remote diagnosis can be hit and miss some times.
eliminating the basics is one way to home in on the culprit.

You say this is more of a mechanical sound than a gas/pop noise
Would you say at a certain rpm this noise occurs?

Is the noise regular and gets faster/louder as rpm climbs?

I took all the spark plugs, all looks ok and then put them back in again.

Just went for another drive.

http://vimeo.com/31292686
and
http://vimeo.com/31292997

Still trying to find the common denominator here. But it could be that, it happens more when after going quite fast (80/90 Kmh) and then slowing down and the sound is very clear.

It doesn't happen all the time, but once it starts, then I notice that it continues when giving power and then at low speeds not giving power and then sometimes when depressing the clutch too. But mostly when depressing the clutch it stops.

It started on Friday and in-between I've put winter tires on and its still doing it. So not specific wheel/tyre related.

got it jacked up and right rear wheel is clicking when rotating backwards.

http://vimeo.com/31294279

So the other rear wheel is fine in both directions. This wheel, makes a klonking noise when manually running it backwards and not forwards. But maybe it needs the weight and the drive to klonk going forwards.

I originally thought this was more related to the engine, as with the engine lid on, it did change the sound a little.

So is this the drive shaft or CV failure. Its hard to say but I think the sound is coming from more near the gearbox than in the wheel, which should indicate drive shaft and not CV joint?

Going to put it into the garage then anyhow.

Well done and a good example of detective work there.

At least it won't break the bank when they fix it as it's a simple enough job.

good news and hopefully at the wheel end of the shaft

mark

thanks all, and I'll keep u posted

garage has said that the drive shaft is broken and is gonna cost 300 euros to repair.

Looks like they are approx 200 euros to buy and 100 euro labour then