Backfiring

[paza1]

Hi everyone. Hope someone can help put my mind at rest. I have been experiencing backfiring as revs reduce, never on acceleration. Plugs are correct NGK, 3 months old low miles and look OK ish (gun metal grey appearance, not sooty). ALDL paper clip test OK. I suspect base timing, what do you think?

[Candles]

Worth setting the base timing anyway, but my car, even as standard used to gurgle on the overrun with the occasional proper 'pop'.

[paza1]

Thanks Candles. I hoped someone would tell me that. I will set the timing as soon as I can find a willing volunteer to help. Forgot to mention that it is a standard car as far as I can see (exhaust 2 1/4" definitely). Can't help wondering if there is any damage going on inside the exhaust/manifold/downpipe. Also, the tickover sometimes seems to "miss" but doesn't get close to stalling...no hunting evident on rev counter or by ear. Dunno if the 2 could be connected? Maybe I am being too picky, only had the car 6 weeks. Paperclip test OK so can't be anything too serious, right

[Monty]

standard exhaust is 2"

[paza1]

Thanks Monty. Is there an easy way to check?

[Monty]

Thanks Monty. Is there an easy way to check?

U`ll have to measure it but not sure if 2" is inside diameter. Have a look were the exhaust goes over the prongeron (front cross member) doest it have a squish in the exhaust if not then it` an after market jobbie.

[Rambo]

Mine also occasionally pops on overrun/decelleration but I think it's normal and, anyway, I like the sound. Makes old grannies crap their breeks as you come up to a junction !!

Mark

[Fubar1764]

Those "pops" are the result of explosions due to unspent fuel getting stuck in the exhaust line and exploding there due to the heat. During acceleration, the exhaust travels out the pipes quickly and don't get a chance to linger in the line to pop.
I have a 2 1/4" straight pipe. No cats, no precat. As soon as the line heats up, I pop under nearly every deceleration from spirited acceleration. Check to see when you backfire. Some backfire isn't necessarily bad. Backfire when cold may suggest that you're not burning fuel efficiently.

[Pete_8lan]

Yes - mine does the same.

It calmed down a bit in the winter when the thermostat wasn't working and the roof was up most of the time.

But with new thermostat, C service, warm weather (hot roads), roof down and sporty exhaust it pops and goes like a good un .

(Rambo I haven't seen any grannies suffering so maybe mine isn't as vocal as yours)

[Fubar1764]

Yes - mine does the same.

It calmed down a bit in the winter when the thermostat wasn't working and the roof was up most of the time.

Oh, well that settles it; the backfire is caused by the roof - leaks and all!

[paza1]

Thanks everyone for your input, most welcome information. It seems that this is a common attribute of the Elan but not everyone experiences this. Does anyone know if it did this out of the factory i.e. popping on deceleration

[stevo]

backfires?

good!

[Dave M]

Thanks everyone for your input, most welcome information. It seems that this is a common attribute of the Elan but not everyone experiences this. Does anyone know if it did this out of the factory i.e. popping on deceleration

No, this is not a stock attribute of the car. With the various modifications (2 different exhausts included) I've done, there has been little to no popping in my car. UK car I'm assuming? For those with the CO2 pot, is this something that could be caused by an improper adjustment?

[John_W]

For those with the CO2 pot, is this something that could be caused by an improper adjustment?

Dave,
Well, that's what the local Lotus dealer adjusted on mine to try to stop the backfiring when I had the SS straight-through exhaust on it. It still popped a bit however - more than I liked - so I replaced the straight-through with a normal baffled silencer and it never backfired again.

Paza, if you have a straight-through silencer you might just have to learn to live with it, but it won't do any harm to check the pipe for air leaks and the check the CO pot and timing.

John

[Engine850]

Your exhaust should'nt be an issue, backfiring is usually caused by one of two things,
a: unburnt fuel in the exhaust
b: greater pressure on the exhaust than on the inlet side

a would be unlikely, if your plugs are not igniting the fuel your car would be running like s**t, and road car don't dump excess fuel like F1 cars etc

b occurs in turbo,s (especially when fitted with dump valves) when suddenly lifting off from heavy throttle. You get higher pressure in the exhaust than you do in the inlet (hence BACKFIRE) .This also can be caused by air leaks, which also will give you a drop in pressure on the inlet side, and poor timing and mixture settings.

I just like the piccy

[tswcowboy]

mine misfires on hard flooring most distrubing

[paza1]

Wow, a lot of info posted here. Thanks everyone. I will be checking my timing tomorrow and post result.
If I am reading all the posts correctly, there seems to be a broad experience of the "popping" on deceleration (with exceptions).
Engine850 - The first part of b would suggest that all Elans would have done this from new.

drop in pressure on the inlet side, and poor timing and mixture settings.

Would this also make for poor running

[paza1]

Checked timing and it was 8 degrees out. This seems quite a lot to me. Haven't given it a run yet. Will let you know how it goes.

[Engine850]

If your timing was that far out you should now get a good inprovement in everything from performance to fuel consumption. Mixture settings (was just general info) are only a problem with carbs, although you'll get the same results if you have damaged or dirty injectors.

tswcowboy, misfires can damage engine components, i suggest you fix this, you could be lucky and just need a set of plugs and leads. If starting is'nt perfect (and it should be) then thats probably all thats wrong.

My elan passed its MOT first time.
A8 goes in next weekend

[paza1]

Just been for a spin after I adjusted the timing. No sign of backfiring, popping etc. Car runs smoother and acceleration is crisper. What a difference Thanks to all for the advice and info.