I turn on the key and pump the fuel a few times. Repeat MANY times. I’ve tried just holding the fuel open about 50% but that normally only gives me a backfire. Once it starts I need to give it a little extra fuel for 30 seconds or so and in runs fine. Normally the first time I pull out in traffic I need to pump a bit extra. After that it’s great. Running PMOs

Half throttle, turn the key, fires in 1-2 turns.

This made a big difference for me:

https://www.partsklassik.com/p-1526-cdi-box-3-pin-new.aspx

-Steve

Two or three full throttle down and up. Turn key, pump throttle. Rev at 2000 to 2500 rpm for a minute, then drive off. Same as 66/67 911. This is cold start. Hot start is simply hold pedal down halfway and crank.

Pull choke fully up on a cold engine, then 2 pumps of the pedal and hold pedal half way down then turn key. Warm engine hold pedal half way down then turn key.

I (sadly) only get mine out a couple times a year, and only when ambient temps over 50.
Cold start:
Turn the key on/off a few times to let the pump run and make sure there is gas in the carb bowls.
Pump the pedal a couple times, turn the key and she usually fires up. May have to 'butterfly' it a little until all cylinders kick in, and hold it around 2000 rpm a few minutes until it warms up.

Warm/hot start: make sure it's in neutral, lean in the driver window, turn the key. No pedal necessary.

I don't think the carbs (original Webers) have been touched in at least 10 years.

NO WAY you should have to do that. Either your technique is wrong or the tuning is off. Hoping you get answers.

I don't know your choke setup, but it should be choked, no pumping, no rigamarole nonsense. Just start and run until it's time to take the choke off. Messing with the pedal should not be so necessary. In fact that's probably when you get the backfire.

You once said you could build a RUF level build. Now's your chance to conquer. You should be able to start it with no pedals touched.

Wouldn't FI be nice about now?

There's no choke on Weber 40IDA. The 66/67 911 Driver's Manual says what I wrote... and to hold down the clutch.

If that's the same as PMOs then Billy is a perfect candidate for FI.

School me, what Porsche carbs don't have chokes? Billy needs a more modern setup me thinks.

PMOs don't have choles either. Neither do all versions of 40IDA, IDS, IDAP, or IDT.
Don't know about Zenith.

Cold start:
Turn key on for 15 seconds - fills the fuel bowls in the carbs - (fuel pressure 3.5 lbs/square inch). Press accelerator down smoothly to 50% position - squirts fuel down the carb throats. Release accelerator, then crank the engine and immediately begin smoothly pressing the accelerator down about 20%. Engine always starts - a little rough at starr up for 5 seconds.
Hot start:
Crank engine then smoothly Press the accelerator pedal down 20% - should start in less than 5 seconds.

Engine is 911 2.7L with Weber’s and Clewett crank fire.

Another flaky answer Rand do you own a 911 powered car or a T4 on carbs ? no chokes on the 6 and even the 4 on carbs as most remove them.
Early Porsche cars (356 ,912 ) had no mauual chokes as the good doctor deemed them as quote " parts you don't need "...end of story.
I have 2 methods ;
when not used for a while,5 pumps on the pedal and around half hand throttle,
when used recently less pumps but no hand throttle.
Back firing is a lean condition on starting caused by undersize idle jets or bad setup (vacuum),if all is good go a touch more rich on the idles,for example I'am running #52 but #50 is better but for ease of starting they work and no black plugs.
The issue is the fuel bowls are vented so the fuel evaporates after sitting,I generally run "key on" for a short time for the bowls to fill again.
Good luck.

https://www.youtube.com/watch?v=qtMXHtJxZ1g


Two full pumps and then about 25% down worked perfect. I'm still liking
these PMOs too much to go FI. There's something about old school tech
that makes me smile. Still working to improve my car. Might never reach
the level of big name builders, but I did it.

Zenith's same.

No Porsche with carbs ever had chokes, they had a hand throttle.
Fifty years later our carburated cars have every kind of variable imaginable.
We operators have every kind of variable too.

Hate to sound like a broken record, but there are no chokes. The hand lever bumps the pedal linkage to open throttles. Used to warm up an already running car when cold by slightly opening throttles above idle (or poor man’s cruise control on long trips).

Key to run fills float bowls. Pumping the throttle squirts fuel from bowls into intakes. I leave the throttles closed during cold starts as this provides the richest condition ( no air) during the start cycle, much like a closed choke does. As it catches, apply a bit of throttle. This pumps a bit more fuel in and allows it to run just above idle.

Exactly like the manual says.

The cracked throttle when hot allows in a bit of air to match the fuel that ended up in the cylinders that probably percolated out of the hot carbs while sitting hot

It is all about getting the right mixture into the cylinders to match what the engine wants for any condition.

The only Porsches I ever had (about 20 plus) that had a hand throttle were MFI induction.

Factory 914-6s have a hand throttle, lots of kits have ben made available to retrofit into conversion cars.

Exact same, except mine would idle right off the bat (ambient 50F min) if I was to let it and I have WEB 120/104 mid/hot cams.

I don't "warm up" my 3.0, I take off slowly at 2500-3000rpm till it warms up, but I have a down hill then a couple minutes of level country road. It's at least 5+ minutes till it's warmed up enough, 10-20+ minutes before my oil pressure starts drop from almost pinned to a normal hot range.

This is one reason I always thought it'd be super cool although highly impractical to switch my car over to MFI... It can be a bear to cold start now w/ Webers. Seldom driven, small battery, and no hand throttle.

Great discussion. Thanks for the schooling.

The Warm start you show is what I've always done on most all carb'd VW's and Porsches with no chokes. Works like a charm.

Just got back from a three hours tour, good 2 hours driving time mostly highway good 1/2 hour driving in town.
The raw sound of the Weber /6....awesome.

From a highly respected source.

and if the motor is well tuned and the ignition is right its not a long warmup time.

With my Webber’s, turn key to accessory and keep it there about 10-15 secs until the tone of the fuel pump goes up and stays there. Two pumps of go-pedal and hit the key.