Help/Advice required...Will only run on full choke, produces white smoke

[A7novice]

Hi all,
I am a comparative newcomer to the A7 scene. I have a 1933 RP that, until recently, has been running very reliably and well.
However, recently it has developed a problem.
 
SYMPTOMS
It will start with full choke and revs freely, but as soon as I attempt to reduce the amount of choke, the engine runs for a second or so then dies. If I return choke to 100% quickly enough, I can prevent it from dying, and it will rev its nuts-off again.
This revving is accompanied by CLOUDS of white-ish smoke from exhaust.
If I persevere, I can eventually nurse the engine by running on choke, until engine is warm and then it will run reasonably smoothly without choke.
 
ACTION TAKEN
I have swapped Carbs.
Swapped Fuel Pump
Replaced Condenser with a new one.
Checked points and plug gaps.
Cleaned carb(s) repeatedly.
Fresh Fuel.
 
Fuel pump is delivering fuel.
I get a big fat spark.
 
Checked for obvious air leaks, none found.
Checked compression (engine cold, throttle fully open, turnover by starter motor.  Readings were 1=95, 2=87, 3= 100, 4=95 )
 
MY ASSUMPTIONS
Need for choke suggests air leak and/or fuel starvation (but have cleaned carb, changed carb.?)
White smoke suggest Head Gasket (about to take head off and change gasket/inspect head, but wouldn’t have thought this would have cause the erratic running/starting pattern I am experiencing?)
Compression readings suggest nothing too seriously wrong with rings and valves (although number 2 is lower than other 3 cylinders)
 
I must admit to being out of my depth, if changing the head gasket doesn’t cure problem………. I will be out of ideas/experience/knowledge.
 
Any suggestions will be gratefully received.


PS. If I have inadvertently broken some protocol in posting this, I apologise in advance, it’s my first go.


 
 

[Reckless Rat]

If your car is still fitted with its original Zenith 26VA carburettor, a regular problem is warping of the carburettor to manifold flange interface, causing air leaks and weakening the mixture. This can be rectiified by removing the carburettor and gently sanding the flange using a pièce of wet/dry on a plate of glass or surface plate.

[Keith Dobinson]

hello A7 novice.  

Suggest you have a look at the head gasket.    Just like everything else   what comes out denotes whats going in.

Blue Smoke = oil being burnt
Black smoke = Too much fuel/ not enough air
White smoke = Water in combustion chamber or if the engine has not been run for a long time condensation in the exhaust system.

Regards

[A7novice]

Thanks for the suggestions, much appreciated.

I intend to change head gasket tomorrow.

Regarding possible warping of the carb./manifold flange....it is a 26VA carb.......I guess I assumed because I had tried two carbs., it was unlikely to be a problem with the carb. However, I will take the advice and have a go at sanding carb. flange on wet and dry placed on glass.

Thanks again.

[Ruairidh Dunford]

Wrapping a wet cloth tightly around the carb to manifold joint will temporarily seal an induction leak and saves you having to remove the carb to check.

If you have access to a compressor you may wish to consider buying a Leak Down Tester - this tool allows you to check individual cylinders for leaks and will also allow you to quickly determine if they being caused by inlet/exhaust valve, rings or gasket. A very useful and relatively inexpensive diagnostic tool.

[Hedd Jones]

I can vouch for Mr Dunfords induction leak test.

[A7novice]

Good idea about the wet cloth, I will give that a go tomorrow.
I do have a compressor, so I will invest in a leak-down tester.

The Austin 7 world seems to be very community spirited, thanks for all the suggestions, all very helpful.

[Bob Culver]

Is water level falling? Any oil or bubbles in radiator? Has oil level increased? Is oil milky or khaki? Is there mayonnaise in the filler tube? Blocks porous through rust now a problem. Posts on old site about the topic with description of bore appearance. Hopefully not the cause! Water in oil is very wearing of roller bearings.

I am intrigued that so many trouble to take compression readings. Gauges came into general use when crank handles disappeared. With Sevens the handle suffices for most diagnosis (throttle open), although a gauge more clearlyy indicates non standard c.r. And by listening can detect serious blow by or valve leaks.

[Peter Naulls]

If you do buy a leak-down tester be sure to check its function first - mine had been wrongly assembled from new and gave meaningless readings. It all adds to the fun!

Peter.

[Tony R]

I am intreged by the leak down tester. There are many very cheap sets on the market it seems. Is it worth buying one of these on fleabay or spend a bit more money on a named brand?