So THAT’s the problem! - Is it????

[Chris Watkins]

A few months ago my wife was driving behind the Stag and reported some puffs of smoke. Oh no! valve guides? Piston rings? But I didn’t notice much from the driver’s seat so nothing got done.
A month ago (and this may be a coincidence) the rev counter - adapted for electronic ignition - started going all over the place, sometimes when other electrics were used, sometimes not - just stopping and starting. And then a bit of misfire.
I ended up taking it to an auto-electrician who reckoned that the wiring was all OK, but reckoned that a classic car guy round the corner had the answer - oil in the dashpots. He topped them up and she ran smoothly! For that day. Then back to bits of misfire.
That’s how I learned about the needle O-rings in strombergs
PicStromberg needle O-ring.jpg
Replaced them thanks to the useful advice at

http://www.bowtie6.com/other/zenith-stromberg-carburetter-repair/

Tested them overnight - dry as a bone
Pictest the rings.jpg
Refitted and she seemed to run well. Then after about 60 miles she was misfiring (especially when booted a bit)

I had a look at the dashpots and they were empty!!! What have I done wrong?
And what would you look at on the electrics next?
Chris

[stag8manod]

Hi Chris, Chuck the Strombergs and fit a 1407 Eldelbrock, with an adaptor plate and jetted to suit, problem solved forever.
Cheers Ian A

[jleyton]

I replaced the seals on mine and cured the problem of dashpot oil disappearing.

I can only suggest going through it all again - perhaps the seals aren't sitting properly or are damaged or of poor quality. Have you lost a similar amount of oil in both dashpots ?

Puffs of smoke could well be these seals (but not much and not for long) but the electrical side has got to be completely separate.

Good luck.

Cheers

Julian

Ps Just one thing to bear in mind - don't think that the oil is just for lubrication, as I did years ago. It dampens the movement of the piston to give a richer mixture on acceleration - roughly speaking, a simpler version of the accelerator pump used on fixed jet carbs.

[DJT]

Chris,

Did you use some fine emery paper on a dowel to smooth out any scratches inside the piston before fitting the new o-rings? The spring washer scratches the bore when knocked out and failure to clean these scratches can result in damaged o-rings. Make sure the new o-rings are lubricated before pushing them in.

[pagan]

I replaced the seals on mine and cured the problem of dashpot oil disappearing.

I can only suggest going through it all again - perhaps the seals aren't sitting properly or are damaged or of poor quality. Have you lost a similar amount of oil in both dashpots ?

Puffs of smoke could well be these seals (but not much and not for long) but the electrical side has got to be completely separate.

Good luck.

Cheers

Julian

Ps Just one thing to bear in mind - don't think that the oil is just for lubrication, as I did years ago. It dampens the movement of the piston to give a richer mixture on acceleration - roughly speaking, a simpler version of the accelerator pump used on fixed jet carbs.

My simply way of determining which to look for first, is.
If the Tacho follows the engine misses then something to do with carby's or mechanical.
If the Tacho leads the engine in misses then it's electrical.

The oil in the Dashpots are for damping of the piston, as far as I now.
otherwise the Dashpots would be too reactive by the inlet pulses.
And Strombergs use the rubber diaphragm to help too.

But the further the Dashpots go up, the richer the mixture.

Allan

[flying farmer]

Sudden swings of the rev counter at the same time as a misfire is almost certainly an electrical problem as the rev counter counts the pulses from the coil. An HT problem will not show up on the rev counter.

I had a similar problem on my Stag engine Estate which only showed on journeys longer than half an hour, not great for confidence on long trips, and took 2 years to find.

Fortunately it finally expired as I backed out of the garage one day, and application of a multi meter showed volts at the ignition switch but non at the coil. It turned out to be a fault in the main loom multi plug, the white ignition live wire wasn't connecting properly and I couldn't cure it so ended up cutting the faulty wire out of the multi plug and connecting it externally. No problems for the last three years

Neil

[Chris Watkins]

Thanks Dave
but I thought my overnight test with oil in the chamber would have checked that.
It's not as if there's much pressure in there?
Chris

Chris,

Did you use some fine emery paper on a dowel to smooth out any scratches inside the piston before fitting the new o-rings? The spring washer scratches the bore when knocked out and failure to clean these scratches can result in damaged o-rings. Make sure the new o-rings are lubricated before pushing them in.

[Chris Watkins]

That's an interesting rule-of-thumb Allan
I'll see if I can apply it in this situation
(but the tacho is all over the place!)
Chris

My simple way of determining which to look for first, is.
If the Tacho follows the engine misses then something to do with carby's or mechanical.
If the Tacho leads the engine in misses then it's electrical.
Allan

[pagan]

Chris
Electronics is quicker responding to what a motor can do.
If the tacho is jumping around quickly, it's getting what is given to the coil, the motor will try to respond to it.
The motors response can not be as quick, but it will be erratic.

Allan

[Chris Watkins]

Wow over 400 views - and some helpful responses
IT"s Sorted! Tacho is rock steady and it's firing beautifully
While I was about to change the electronic ignition unit I found a small amount of rust and gunk on the distributor shaft just below the magnetic collar.
Just cleaned it off and a bit of silicone spray
Who would have thought?
Chris

[V Mad]

Wow over 400 views - and some helpful responses
IT"s Sorted! Tacho is rock steady and it's firing beautifully
While I was about to change the electronic ignition unit I found a small amount of rust and gunk on the distributor shaft just below the magnetic collar.
Just cleaned it off and a bit of silicone spray
Who would have thought?
Chris

[jleyton]

Wow over 400 views - and some helpful responses
IT"s Sorted! Tacho is rock steady and it's firing beautifully
While I was about to change the electronic ignition unit I found a small amount of rust and gunk on the distributor shaft just below the magnetic collar.
Just cleaned it off and a bit of silicone spray
Who would have thought?
Chris

And the carb O rings ????

Cheers

Julian

[Chris Watkins]

Chris
I agree with your sentiment entirely!
Chris

[Chris Watkins]

Julian
The carb O-rings are still leaking nicely
I carry a can of 3in1 at the moment!
Chris