Hunting and Stalling at Tickover

[Martin Baker]

A bit of a poser.

My Speedy has been driving very sweetly until earlier this week. I drove to my gym stopping to buy petrol on the way. On leaving the petrol station the car stalled but started easily. When I got to the gym it again stalled.

It drove home very well with perhaps a hint of a miss. Again it stalled as I put it away in the garage. On restarting, it picks up well and revs normally.

I gave it a dose of looking at earlier, checking and cleaning the carb, removing and checking the plugs, tweaking the timing but all to no avail. It will only tickover with greatly increased revs.

This is a Speedy engine with Sports manifold and downdraft Zenith, Paul Bonewell cam and followers and Accuspark distributor. What can have changed? My only thought is perhaps in putting petrol in the tank disturbed sludge which is causing a partial blockage (I've definitely experienced that sort of problem with our 1938 Pearl).

Suggestions and ideas please!

[Ruairidh Dunford]

Under normal circumstances, yes.

There is no condenser in an electronic distributor however.

["Slack Alice" Simon]

I haven't had those symptoms.

I have had, and am still having, lots of fun with detritus in the tank.

I have had to stop and blow it back down the main fuel line twice, lots of blocked jets, and I think it once got under a valve in the fuel pump.

Before that, the fuel pump behaved erratically, working for ten miles and then stopping.

That was down to an aged diaphragm which worked when cool and didn't work when warm.


I would drain the tank - I have a cut open 5 gallon plastic container which I use - and see what comes out, if you think there might be a problem there.

[Charles Levien]

I’ve experienced this problem with the Opal in unusually hot weather — also experienced going up the Gross Glockner which subsequently turned out to be a slightly loose union which was letting air in and weakening the miixture.

[John Cornforth]

Hi Martin

In the past, I have found that stopping for petrol is exactly the right time for carburettor temperature to peak due to under-bonnet heat soak. Normally, problems only experienced in exceptionally warm weather. The other danger period is idling in traffic, which I try to avoid !

A hot enough carb seems to suffer from vapour bubbles in the float chamber, which upsets the mixture. Any shortcomings in the ignition system can worsen the stalling/misfiring/surging effect, but I doubt that's a factor in your case.

Putting in petrol could have disturbed something in the tank, but the contents slosh around merrily anyway during normal driving so that seems unlikely.

I normally use BP Ulitmate 98 octane, and haven't had vapour problems for a long time. No idea if the two are connected, or if so, how.

[Nick Turley]

It really sounds like dirt Martin.
I would suggest taking the top off the fuel pump and removing its filter.

[John Mason]

It could be air starvation. When the throttle butterfly is fully closed as with Zeneth 26VA carbs. I am not familiar with Zeneth down draught carbs do they have a similar air jet direct to the Ventura tube.

John Mason

[Martin Baker]

Sorted!

Blew out the carb jets (again), cleaned out petrol pump (no obviouis detritus) then blew through petrol pipe to tank with airline. Tickover now sweet as a nut again.

Don't you love it when a theory proves correct!

Thank you everyone for your help and suggestions.