Venting Weber carbs

[Porsche 2]

How do you drill/vent Weber 40 IDA carbs to eliminate heat gas expansion and gas leaking when shutting down a hot engine? Will also be adding the insulating thick gaskets between the carbs and manifolds.

[MBruns]

There is a fixture to drill holes in the top cover of the carb body, along with insulators between the heads and manifolds that will take care of the percolating issue, providing float levels and fuel pressures are in spec. I have the fixture and you are welcome to use and return it for the cost of shipping.
Mike Bruns

[Porsche 2]

Thanks Mike, you are very generous. I have someone lined up now to do this for me.

[Trackrash]

This is an interesting question. One I have been struggling with.

I actually have, I think, two issues.

I have actually had the gas boil, it sounded like a coffee peculator. I guess the solution to that is more or thicker insulating under the manifold.

The other issue is gas SOMEHOW leaking out after shutdown mainly in #1. This is causing flooding and fouling of that plug. I will notice a couple of drops of gas coming out of the throttle shaft. It appears that gas is siphoning out through the idle circuit?

FWIW. I had drilled those extra vent holes, as mentioned, many years ago. Recently I enlarged those extra vent holes. NO CHANGE. I more recently PLUGGED those extra vent holes. Again NO CHANGE.

Yea, yea, I checked the float level, float action, replace the needle and seat TWICE. I will start a thread on this after I do some more testing......YMMV

[MBruns]

The insulator kits from PMO work well, they come with longer studs gaskets and insulators, start with that and assuming your engine temps are in line you should be good
Mike Bruns

[Trackrash]

Originally Posted by MBruns

The insulator kits from PMO work well, they come with longer studs gaskets and insulators, start with that and assuming your engine temps are in line you should be good
Mike Bruns

I have insulators between the manifold and heads. Are the PMO's thicker or better than what is generally available? Any pics?

What can be done to keep the engine temp in line AFTER the motor is shut down?

[Steve@Rennsport]

I think its time to mention that Weber float levels are critical and MUST be perfect,....not just very close, but perfect. This assures consistent running/jetting, driveability, performance, and minimizing fuel percolation issues. Fuel pressures must be regulated to 3.5 psi, too.

Short of installing a pair of exhaust fans under the engine grille, there isn't anything you can do to reduce engine temps during heat soak.

[Trackrash]

Originally Posted by Steve@Rennsport

I think its time to mention that Weber float levels are critical and MUST be perfect,....not just very close, but perfect. This assures consistent running/jetting, driveability, performance, and minimizing fuel percolation issues. Fuel pressures must be regulated to 3.5 psi, too.

Short of installing a pair of exhaust fans under the engine grille, there isn't anything you can do to reduce engine temps during heat soak.

Steve, thanks for the response but please define perfect. The vile used to measure the level has two lines. The fuel level should be set between these lines, correct?

I have found that it is best to have the fuel level towards the lower line.

Am I missing something?

[Steve@Rennsport]

Hi Gordon,

Those vials are designed to be used for Zenith as well as Weber 3bbl carbs, hence the two set of lines. The upper ones are for the Webers and the lower set is for Zeniths.

The float level is perfect when the meniscus rests on the lower line with edges against the upper one. Naturally, the engine needs to be running when viewing the gauge and deciding what to do.

These markings are calibrated for 3.5 psi of fuel pressure so thats the place to start the whole process.