Austin Big Seven starting problem

[Thowdfella]

I have mentioned this problem before but never managed to sort out the problem. The carb is a Zenith vm-4 which appears to be in good condition with no worn spindles. It has now got to the state where it will not start at all. I have done a valve grind; there is no sideways movement on the pistons; the compressions are all around 70 when turning the engine over on the starter motor; the timing has been checked again and again and ignition laser indicators on the plugs are all  flashing. When the head was off we checked the camshaft timing which appeared to be correct. but still wont start. Last night when I was doing a last ditch attempt to start it - I forgot to turn the ignition switch on. When I did turn it on and tried it - it eventually kicked into life!
To me this suggests petrol starvation so its back to the carb. on previous occasions when it wouldn't start, I have removed the float chamber - filled it to a higher level than what was in there and then it started. Can anyone help / I am using fresh fuel and priming with the fuel pump lever and its a new pump which gushes fuel out .

[John Mason]

Yes I agree with you aboutit being a fuel problem if as you say you have a good spark and compression. Does the car run ok once started ? Could it be a choke problem and plugs being flooded ,rather than fuel starvation .

John Mason

[Roger Goldthorpe]

Check the choke. Full story below.

I had a problem starting my RP when I first acquired it. On delivery I was given a demonstration of how to start the engine. The vendor, a tall man, suggested that as I was also tall I could follow his starting procedure. The main point here is that he reached under the bonnet and with his right hand lifted the choke and with the left hand swung the starting handle and off she went first swing. Being new to 7’s I didn’t fancy this approach and so operated the choke in the conventional way. Over the next couple of days I lost about half a stone swinging and swinging the handle. When it did start the engine ran fine, the problem was getting it to start the first time. Determined to find the cause of the reluctant starting I cleaned out the carb and the engine started ok. Problem solved. Next day engine refused to start so off with the carb another clean out and again the engine started ok. On the third day the engine refused to start. I concluded that if by cleaning and in the process flooding the carb then the problem was somehow related to fuel/fuel air being sucked into the engine. Examination of the choke cable revealed that the cable had pulled through the nipple resulting in only partial choke being applied. Nipple adjusted problem solved. The previous owner had never used the ‘choke’ as he had always operated this by reaching under the bonnet so would never know the nipple had shifted.

Roger Goldthorpe

[Thowdfella]

It's only started once in the last 10 long days  so difficult to say if it runs ok.
After the valve grind it started and ran fine for around 15 minutes. Then took it up the road and it stopped never to start again. Rechecked compressions - OK, and checked all timing ecetera. I have the filter off so can see the choke is closing oK but agree it could be flooding as when I remove the carb there is a pool of fuel - not water - at the bottom of the inlet. Manifold. But what causes the flooding? Just stripped the carb yet again and everything is clear. It's trying to start but can't make it!
Could do with a new carb although this has been overhauled.

[Colin Wilks]

I hope I'm not teaching granny to suck eggs here, but have you confirmed the action of the float bowl needle valve is correct? If it's not closing correctly excess fuel will enter the carb via the orifice opposite the choke spindle and will keep on coming.

[Thowdfella]

I hope I'm not teaching granny to suck eggs here, but have you confirmed the action of the float bowl needle valve is correct? If it's not closing correctly excess fuel will enter the carb via the orifice opposite the choke spindle and will keep on coming.

Thanks for that but yes. When I fill the carb by using the pump lever after about three pumps it stops and won't put any more in. Also I have just had the needle valve out and checked it and it's fine, in fact it's a new one. If I take the plugs out they are soaking wet. I put a new condenser in a little while ago so just to prove it's not that I pit the old one in but no difference.

[Reckless Rat]

If the plugs are soaking wet it suggests that there's an ignition problem somewhere. If there carb has been overfuelling and the plugs have been running rich then the spark is likely to break down under compression. Have you tried a different set of plugs?

[Chris KC]

If I might throw in a wild thought, when did you last put fresh petrol in the tank?

[Roger Goldthorpe]

Plugs tested out of the engine (laid on cylinder head) may indicate a good spark but as Reckless points out the spark can fail under compression if the electrics are suspect.

Roger

[Tony Press]

I have mentioned this problem before but never managed to sort out the problem. The carb is a Zenith vm-4 which appears to be in good condition with no worn spindles. It has now got to the state where it will not start at all. I have done a valve grind; there is no sideways movement on the pistons; the compressions are all around 70 when turning the engine over on the starter motor; the timing has been checked again and again and ignition laser indicators on the plugs are all  flashing. When the head was off we checked the camshaft timing which appeared to be correct. but still wont start. Last night when I was doing a last ditch attempt to start it - I forgot to turn the ignition switch on. When I did turn it on and tried it - it eventually kicked into life!
To me this suggests petrol starvation so its back to the carb. on previous occasions when it wouldn't start, I have removed the float chamber - filled it to a higher level than what was in there and then it started. Can anyone help / I am using fresh fuel and priming with the fuel pump lever and its a new pump which gushes fuel out .

You say-

"the compressions are all around 70 when turning the engine over on the starter motor"

Presumably with the choke open and turned a few times to get some oil around, this seems low for a good engine with pistons and valves tight 

 Are they all at 70 psi ?

Cheers, Tony