Sorting out a popping valve

[Thorssen]

Hi

A bit of advice is needed. I've got an 83 Devon 1.9 petrol. I'm getting intermittent popping from the engine with the obligatory loss of power, which all points to a valve not sitting right (I think although I'm no expert).

I've been told by a friend that is more used to Aircooled that waterboxers are prone to the bolts snapping and I could be opening a can of worms when trying to remove the cylinder head / get into the valves.

I just thought I'd ask the forum for a consensus, as she's had a fair bit done so far this summer and is only just back on the road. I'm torn between trying or just limping her along for a bit and going camping nearby (also my pocket money is getting a bit low).

I'd welcome any wisdom

[john1]

is it on run down? Going down hills with foot off the gas?

[Thorssen]

I'm not sure what that means? Certainly using gears, dipping clutch, stopping and letting it idle all helps - sometimes

[kevtherev]

it means when you are traveling down a hill, and in gear, with your foot off the acc pedal ,does it pop then?

or does it do it when you are accelerating through the gears

[Thorssen]

No popping when in gear and going downhill that I've noticed, it's only happening when I'm asking something from the engine. But intermittently.

I ran it on a road yesterday 8 miles of steady climb, popping came in around mile 2. Pulled in around mile 4 left engine idling or 5 mins, then went off again, and it was perfect for the rest of the journey including the return.

I've changed plugs, flushed and given her new oil.

[kevtherev]

Ok it was important to be sure about that as it narrows down the reasons.
popping on acceleration is a fuel issue, and it may be a fuel delivery problem, pump, filter, pipe kinked, carb filter blocked... you must eliminate them one at a time, start with the filter next to the tank.
I will hazzard a guess this doesn't happen when it's cold and the engine is warming up?

[Thorssen]

Thanks. It never happens immediately after starting, but can happen within the first half mile or so, before the engine is up to temperature, Once the popping is there I struggle to get past 30 / 35 if there is type of gradient. When it's not there she runs fine and pulls well

In you're experience, the lack of occurrence when I'm not pushing on the accelerator makes it more likely to be fuel than a valve not sitting right?

Sorry if these seem daft questions but I'm fairly new to this

[kevtherev]

Thanks. It never happens immediately after starting, but can happen within the first half mile or so, before the engine is up to temperature, Once the popping is there I struggle to get past 30 / 35 if there is type of gradient. When it's not there she runs fine and pulls well

In you're experience, the lack of occurrence when I'm not pushing on the accelerator makes it more likely to be fuel than a valve not sitting right?

Sorry if these seem daft questions but I'm fairly new to this

I would also suspect compression and or timing. but your description suggests a fueling problem in my opinion.

Popping is a result of a weak mixture not igniting in the cylinder when the spark is there, the unburnt fuel charge then gets pushed into the exhaust where either the hot exhaust or the wasted spark ignites it....hence the "pop" noise.
As you depress the accelerator the butterfly opens and a huge vacuum pulls the correct fuel air mixture into the cylinder, if there is insufficient fuel in the carburettor float bowl, more air than fuel is drawn in

Engines with an air leak do this on the over run.
Your engine does this on acceleration, and it's intermittent nature suggest fueling

ensure your engine has a good supply of fuel first before suspecting the worst case scenario

[Thorssen]

Many thanks for your advice

I'll have a tinker

[Thorssen]

Hi

Thanks for the advice.

I've changed filters, and its definitely better, but still not quite right.

So far, I'm never getting the popping in gear down hill (even with a good play in the peaks). She is pulling better from 1st to 3rd, although I do get the odd juddering issue on acceleration that feels (to me almost as if she has stalled and bumped again), usually only 1-3 times and occasionally accompanied by what sounds like a miss-fire.

On a relatively flat stretch of sunday morning dual carriageway I can coax 55mph, throw in a slight incline and I'm flat out 45-47mph. That said, she did get up a very steep valley climb (around 2 miles of 1:7 with hairpins) in 2nd with only a few words of support and encouragement.

the engine is 1.9 petrol.

Any more thoughts or advice much appreciated..
C

[kevtherev]

OK..it's time for a compression test.
post the results up here

[Thorssen]

Cheers will do

[California Dreamin]

Definately check the compressions as Kev has suggested.
Popping sounds could well be a burnt valve but I'm unsure why the symptoms should come and go....this fault would be permenant....
But
The intermittant nature of the faults suggest that there is something else...fuel starvation or ignition leads/distributor cap/plugs shorting to ground under load perhaps.
The compression test will give a general indication of the engines condition/fitness.

Martin