Cold start difficulty

[silverboydreamer]

I have a 63 T6 that I have just finished restoring and am having a problem with getting the engine started from cold.
The plugs, battery (6 volt), ignition switch combined with a starter relay and leads are new, the points, dynamic timing ( 5 degrees, 3krevs- 35 btc) and tappers are in spec,
The carbs (zenith) have been sonically cleaned with new pistons, seals and gaskets, I have setup carbs to match same intake volumes in low and high revs, the enrichment tubes work and can be seen to inject fuel when throttle pumped, the air screws have been adjusted to each other and throttle linkage equalised, tick- over is around 900 rpm.

When cold I turn engine over for 30 secs then pump throttle 4-6 times, then with part throttle I turnover the engine, no matter how I try it will not catch, however if i spray in easy-start or drop petrol down carbs the engine starts and can be caught on the throttle .After engine has run a little it starts on the button.

Does anyone have any answers as to what I might do to sort this out as I don’t want to have to keep using easy-start to get the engine going

[Nine One One]

Have you tried pumping the throttle 4 times, holding the throttle on part depression, then turning the engine over, to start?

Cant really see the point of turning the engine over for 30 seconds unless you are making sure the oil pressure light is going out, and pre priming the oil system, before then trying to prime the carburettors ??

If its not been started months I can see the point of making sure you have oil pressure in the system before starting, but not if used daily?

Once the engine starts just feather the throttle to keep it running till warmed up.

[Lightweight_911]

How old is the fuel ?

Those are classic symptons of 'stale' fuel - I have had the same symptoms with my Climax-engined Seven after a winter lay-up.

Modern petrol 'goes off' within a matter of weeks nowadays - not a problem for modern electronically-managed engines but can often create starting difficulties with older classics.

[roy mawbey]

Okay, a few things to try that might work for you.

1). Clutch pedal to floor, depress the accelerator half way and then start the cranking directly the green oil light goes out, continue cranking for another 5 seconds then start pumping the accelerator maybe 4 times to the floor. During that process it should fire up and you will need to stop the starter cranking.

Modern fuel will evaporate the fuel bowls in a couple of weeks and the initial cranking will be longer than if you used the car only a few days before. It can take almost a minute if they dry out completely Is your fuel very old? It does not age well.

2). The accelerator pumps do seem to hold the fuel better an its encased in the small cylinders with the leather type skirt.

3). Is your crank speed fast and does it stay fast while cranking? If its slow the fuel delivery will take longer. I presume the battery is fine.
4). If your engine starts great after its warm by just turning the key and holding the accelerator half way down then I would think all is okay with the ignition and carburation.

On very cold days I found getting in the car turn on the fuel and just pump the accelerator 4 or 5 times to the floor, clutch to floor and then crank to start would fire it up but, not always enough to keep it going. Summer time no problem on first start up that method always works.

Best of luck
Roy

[Kenyon]

I have the same problem. I have come to the conclusion its a fuelling / fuel issue. It sounds like I have similar cold start issues as you. If I leave the car for more than 3 days it's a case of priming the carbs a couple of times or easystart. Starting the day after a run is fine.

I think it's a combination of new fuel evaporating (or returning from where it came) and a lack of priming pump.

I am going to go down the manual prime pump route when I get round it.

Fairly confident it's not an ignition issue as I have a new Optima Red Top, new Bosch coil, 123distributor and new(ish) leads and plugs.

[marc500]

My t5b is the same.... I have to pump gas peddle, turn it over 5-10 secs, pump peddle a load more, repeat.... for a good few minutes. Eventually it will start to fire but still not enough fuel there for it to take properly (my right hand carb doesn’t fill as quick as the left hand one, bit of adjustment needed there for a rainy day). So keep pumping... eventually it bursts into life. I can shortcut all the above by tipping some fuel down the tops of the carbs. The longer it has stood the more stuborn it is! It starts instantly if used a day or two prior. I guess today’s fuel evaporates out the carbs fast, plus fuel getting stale in the tank and maybe a bit of fettling of my accelerator pumps needed. I tried putting in a hand primer years ago but it sort of collapsed and starved off the fuel after a few minutes driving. An electric fuel pump would solve all of the above but where is the fun in that.
Edit: I don’t think my fuel pump is too clever either, I have a rebuild kit to go on it but haven’t got round to fitting it yet

[mycar]

Is it not the case that the 356 engine must be turned over to for the fuel pump to prime the carburettors ?

With the early 911 you turn the key to 1 and the electric fuel pump clicks away, nicely filling the fuel bowls. When the clicking stops the key is turned again to engage the starter and the engine roars into life.

With the 356 engine the fuel pump only pumps when the engine is turning over. My preferred method when the carburettors are dry is to twist the key and turn the engine in 5 second bursts with a little rest in between so not to stress the electrics. A healthy engine setup should catch within 6 or seven attempt even after being left for a month without being started. With full fuel bowls the engine should start within a turn or two.

I've found that having the correct carburettor float levels is important as is the correct advance. And nice fresh fuel.

Not sure Easy-Start type stuff is brilliant for your engine.

[POR68]

You are getting good, practical advice here. They can all be a bit of a pain to start cold after a layoff. I have fitted a cheap inline electric pump under the passenger foot panel and prime the carbs with that for a 15-20 seconds. I then turn it off and give the accelerator a couple of pumps and turn the key with about 25-30% throttle. Works well and saves a lot of cranking to get the fuel into the bowls and tubes in the carbs. I can add that I always reduce the amount of residual fuel in the carbs at switch off by shutting off the fuel cock as I near my house after a run. There are lots of electrical suspects here but this sounds like a fuel/carb issue.

[silverboydreamer]

Thanks for all your replies, the consensus appears to be that my problem is not unusual and looking at the sites in the states they seem to have it too with their answer to it being down the electric fuel pump route ( as a primer ). I think it’s a priming problem and for the time being will investigate that.
Thanks for your comments

[neilbardsley]

Don't bother with a electric primer. You can put a bulb pump in line if you want. Never crank for more than 10 secs. Do you have the battery on a trickle charger? I've found that battery charge is normally at fault once fuel has made it to the carbs

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[POR68]

Neil, I found that the electric primer had another use. When the diaphragm on my mechanical fuel pump failed on a drive, I could use the low PSI electric pump to get me home. I could then repair the mechanical pump.

[roy mawbey]

Neil,

Leave your car for a month then try to start it on your 10 second crank. I see 50 seconds of crank before it goes. Thats why my engine is started every week. Because of Ethanol petrol we have these days the best way out of this is an electric pump behind the floor board. One you can switch on and off easily.

I did a test on the evaporation on the work bench a while ago I was amazed how fast it went. After my spell in hospital in Dec/ January and then trying to start the 356 late that month It took around 50 seconds on fast crank to start.

I can say, when you go down the easy route of getting in and just pumping the accelerator to the floor 4 or 5 times and turning the the engine often will fire up but if it doesn't catch and you try again and again pumping then when it finally does its often is running on 3 cylinders choked up and then takes a few minutes driving to come back on full four.

I saw a youtube of ' Heidi and Franny ' who post 356 workshop video's and one details their start up of their 356 after 2 months without using it. It details these questions we have raised well.

If Porsche had designed the car with enough room for the Zeniths to have a choke that might have helped no end.

Roy

[neilbardsley]

I don't disagree. Sometimes it catches immediately. Often it needs 2 to 4 ten second tries.

However I think that having another pump inline isn't the answer.

I would be tempted to change the mechanic pump to a electrical.

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[decapman]

I also had exactly those symptoms
An electric primer and an Optima 6v battery later ( red) no more problems at all
The primer has a discrete button under the dash (I prime for 20 seconds).
The ugly red Optima has a battery cover over it to hide it.
I find that it has a far more powerful kick
Funnily enough my 356 friends in the US all swear by them especially for cars that can sit for a spell between use

[marc500]

I like the Heidi and Franny youtube videos!

They cranked that 356 for nearly a minute... made me feel like mine isn't too bad. I wouldn't want to crank my starter for that long, it feels stressful. I'd opt for shorter bursts of cranking and more peddle pumping.

The point about benefits of building up oil pressure prior to it firing is a good one.