911 2.7L Vacuum Leak

[gtfhercules]

Hello all,

I have a 1977 US market (non catalyst, California market) 911 S that has a nasty vacuum leak that causes the car to surge badly when started cold and causes it to quit. The problem wasn't that bad earlier this year (as in if you drive it a mile or so it'd be fine) but during the last rally I attended in the tail end of August the car was running poorly for miles on end until I got to the start point...and at that point it ran totally fine for the rest of the 100+ mile event.

The weird part is that if I were to let the car sit overnight and turn it back on the next day, it would run fine - but if I were to let it sit normally for at least a week if not several weeks, it would run roughly and die.

However, my problem is as follows:

The smoke was coming out from what looks like an area between the fuel distributor and the CIS intake boot. I took the boot off and inspected it for any cracks and I could not find any. Is there anywhere else back there that I should be looking?

Here's a video I've shot of where the smoke is coming out of.

Thanks so much!

[allaircooled]

Looks like the smoke is coming out the port where you adjust the idle mixture.

[Paulporsche]

I wouldn't think that small amount of smoke from the idle mixture screw area would be the cause of your problem, but to be safe, try plugging it with something and see if you get the same symptoms.

Is that the only area you saw smoke?

You should check your ignition components, including your points gap, rotor, cap and wires.

Then you need to verify your control and fuel pressures with a gauge. This will help you determine how well your Warmup Regulator (WUR) is working. There are a lot of threads on how to do this, so you should do a search, but there are several people on this forum who can guide you through it. Once you do this you should verify which WUR you have and post the results.

You say you have a California car. Are you in California? When measuring the cold control pressure, it's important to know the ambient temperature.

My 77's original engine had a 033 WUR. I'll post a graphic showing the control pressure chart.

[Paulporsche]

[boyt911sc]

Originally Posted by gtfhercules

Hello all,

I have a 1977 US market (non catalyst, California market) 911 S that has a nasty vacuum leak that causes the car to surge badly when started cold and causes it to quit. The problem wasn't that bad earlier this year (as in if you drive it a mile or so it'd be fine) but during the last rally I attended in the tail end of August the car was running poorly for miles on end until I got to the start point...and at that point it ran totally fine for the rest of the 100+ mile event.

The weird part is that if I were to let the car sit overnight and turn it back on the next day, it would run fine - but if I were to let it sit normally for at least a week if not several weeks, it would run roughly and die.

However, my problem is as follows:

The smoke was coming out from what looks like an area between the fuel distributor and the CIS intake boot. I took the boot off and inspected it for any cracks and I could not find any. Is there anywhere else back there that I should be looking?

Here's a video I've shot of where the smoke is coming out of.

Thanks so much!

Hercules,

You are doing the smoke test incorrectly. You need to isolate the air box from atmospheric condition to test for air leak/s. Where are you injecting the smoke for your test? Keep us posted.

Tony

[gtfhercules]

Gentlemen,

Sorry for the delay - I literally can't recall what I did Thursday, and yesterday I spent a good portion of my day doing my SC's brake hoses which are unknown years old. Not like that car doesn't have another 69 problems...

Anyhow, if I recall correctly, I conducted the vacuum test by pulling the hose in the first image and pumping smoke in there. To block the airbox off, I simply put a bag on top of the airbox with the filter still on, as I could not see an easier way of closing off the whole area.

I'll look into testing fuel and control pressures - what tool(s) would I need to do conduct that test?

I was going to look into getting a CO meter as well but the prices for those caused me to balk a bit

I'll also look into checking the rest of the ignition system...somewhat related, but is there a logical reason why my tach only revs to ~5.5k? I thought redline for these 2.7s is around 6.2. It annoys me because I put my redline at 12 o'clock and it never gets there!

Thanks so much for the help so far,

Herc

[Paulporsche]

When checking ignition, make sure your points are gapped correctly.

To check fuel pressures you need a fuel pressure gauge with connections for CIS.