Car: '74 2.0L with Dual Dellorto DRLA Carbs

Symptoms:

Shaky after startup, seems to have dropouts while idling, sounds a bit like chugging from passenger side of engine on acceleration, overall performance lackluster. But the most glaring problem is that I can hold my hand over number 3 carb throat and there is practically no choking off of the engine. Number 3 is definitely firing, because if I close its mixture screw then the engine does stumble. All the other cylinders stumble as expected if I hold my hand over their carb throats.

What I have done so far:

Adjusted valves to spec.
Completely rebuilt both carbs.
Refreshed ignition components.
Tried some different timings.

Also did a compression test with the following results:

CYL #1 #2 #3 #4

DRY 110 110 110 115
WET 120 120 122 118

Problem remains. Am I leaking at an intake manifold? Any input/advice appreciated.

Ansbacher

Really hoping to get some help on this.

Ansbacher

The easiest way to find a vacuum leak is to spray carb cleaner on all the gaskets, joints, or hoses and listen for a change in the engine note.

Great advice, I am chasing down one of these vacuum problems as well, will try this test!

What are you using for intake base gaskets?

Rather than an oil based spray over your nice clean engine, try this from the Bosch Guide:

EXELLENT Jeff!

Rhodyguy:

I am using a very generic looking gasket I think I got from CB Performance. Do you know of a "preferred" and beefier type gasket to use? Or, what is the best material to use to make my own?

Ansbacher

You Tube has vids on ho-made smoke testers for vacuum leaks. a new empty paint can and some charcoal and cardboard. Attach your compressor and a cheap harbor freight regulator and you will find more vacuum leaks than you thought possible.

Who knew your distributor oring can leak...?

Just a thin piece of gasket material? Totally wrong gaskets. Even with carbs they suck. You want to source the correct phenolic bases. Avail from the usual suspects. They come in 3 and 4 stud hole varieties. I wouldn't go any further until you purchase and install the correct items. The phenolic gasket bases help with heatsoak up the intakes.

As usual, I think I was barking up the wrong tree suspecting my intakes. I had recently installed a new accelerator cable and my attachment to the hex bar was not oriented at 90 degrees. I think it was torqueing things out of whack when it pulled. Adjusted it and now the symptoms are gone and the car is running great.

Rhodyguy - thanks for your advice. I will search for better gaskets. As far as phenolic spacers for the carbs, I tried them when I had a 356 Porsche and saw no discernible difference in regards to percolation- Florida is just too hot in the summer!

Thanks everyone,

Ansbacher

Wait a minute. You (Rhodyguy) are talking about phenolic spacers for the intakes at the block??? Never heard of those.

Ansbacher

those are the standard 914 intake blocks which work as insulators from the hot engine and also seal really well.

The stock FI units should work for you. Off brand ones at pelican run $9. $20something for genuine Porsche.

The gasket kit that for total rebuild comes with the phenolic spacers he is talking about. THey come with paper on one side, maybe both, I can't remember for sure. BUT I do remember that my kit also came with aluminum plates of the same shape as the intake.

Not knowing what the hell I was doing (or having any directions), I used the aluminum plates AND the phenolic spacers on my FI car. Well it did not blow up or anything. But as I started hunting for my 1st vacuum leaks and added pictures.... The carb guys spoke up and said that I should only use the phenolic on the FI intakes. The aluminum ones were for carbs.

the aluminum gaskets were crushable. Maybe someone will step in and straighten me out again.

Orange circle is the phenolic. Green are the crushable washers. Since there were 8, I figured one on each side of the phenolic block at each intake. I was corrected. If I were doing carbs and taking advise, I would use the aluminum.... but don't trust me, seriously keep listening.

Click to view attachment

Try part #039-129-707. Should be for 2.0, 3 stud heads. Ensure the intake bases are true. I like to tighten them up in stages, sort of an X pattern, to make sure i don't build in a leak. I've never used gaskets made from aluminum.

The aluminum ones only work well with the stock intake manifolds/carbs. They do not work (seal) well with aftermarket manifolds-carbs.

For the best intake manifold gaskets....

http://vwparts.aircooled.net/HP-Type-4-Int...fold-gasket.htm

The Empi ones are not great also,they are too thick and compress and cause leaks when the nuts loosen up,bought a set of nos CB ones off the Samba years ago and that came with good thin gaskets .
The alloy gaskets are fine if both surfaces are clean and flat,the FI ones are the best however.

The thin metal ones are best for an OEM carb manifold set up.

The FI spacer/gaskets are best used with an FI manifold setup not carbs. They won't last on carb set up.

The gaskets John sells at Aircooled.net are the best ones I've ever used for a dual carb set up. Before use coat each side with Chapstick.