Weber Tuning air intake

[Antal]

I am a first time user of this forum. I have been reading a lot on it but haven’t found any messages regarding the issue I am having with my Porsche 911 2.2T from 1971. I have owned the car for 9 years now and I have to say it always ran but never perfectly. I am using it only to do some nice day cruising and not on the tracks so maximum power isn’t really what I am looking for. My focus is more on reliability. Last year I have had some issues with leaking floats so I decided to redo the carburetors (Weber). First thing I did was to clean the 2 pieces in the dishwasher which my wife didn’t think of as a good idea but nevertheless, they are clean now. Cleaned all jets, nozzles and mixture adjustment screws using compressed air. Replaced all gaskets and rings and put it back on the engine to start working on the tuning. I found a very good piece on this forum on how to tune the Weber carburetors.
The car fired up immediately at the first try; so far so good. The issue started when trying to synchronize the individual air intake. Carburetor 4-5-6 are very close at idle as well at 3000 rpm however it seams that 1-2-3 only get air from above at high rpm. At idle, air intake is virtually nothing e.g. when I place my hand on the individual air intake, the engine doesn’t go down in rpm but when I do it on 4-5 or 6, the engine immediately falls back and even stalls. Changes to the air correction screw doesn’t make a difference in the airflow. The engine is running on all six so air must come from somewhere. I checked the valve clearance and that seams to be OK. Maybe not perfect but close enough. The car was running with the current valve clearance before the carburetor overhaul so I don’t see an issue here. The gaskets between carburetor and intake manifold have been replaced by new once but the gaskets between manifold and engine, I haven’t touched. I however don’t think it has to do with gaskets as it involves all 3 which would be much of a coincidence.
Is there anyone who has had the same issue or who has an idea what the issue might be?
Your reply would be very much appreciated.

[JohnJL]

Have you checked for inake manifold leaks by spraying some carb cleaner (a little at a time) at the manifold gaskets? It sounds like maybe your1-2-3 bank is not on straight and is leaking at the heads.

[Mo_Gearhead]

I agree that you must have an air leak in the manifold to carb. area.

Placing your hand over the individual intakes (1-2-3) with a running engine and NO discernible draw/suction???

You say you did not have the manifold off. No leaking gasoline at the carb. gaskets? Are you certain you replaced the carb. gaskets (where the tops come off the carbs.) correctly?

That particular carb. does not have the vacuum tube openings does it? Are they properly hooked up or sealed/blocked off?

Puzzling???

[Antal]

John and Mo, thanks for your quick reply. To answer your questions, I did spray some (in my case) starter help on the gaskets to see if rpm goes up but nothing. I will do it again just to be sure. There is no leaking gasoline at the carb so I don't think air is going in there. The gasket on top must be right because there is only one way it fits or......? My carb doesn't have the vacuum tube. What is the idea with this question?

I will try again for leaks with a carb cleaner and I am also thinking of taking the manifold off the engine to see what is going on there as I haven't done that yet.

Thanks again and any ideas are still welcome.

[911pcars]

The only thing I can think of is that the throttle plates for Weber 1-2-3 are completely closed at idle. That so? If so, you won't feel any engine vacuum by placing your hand over the throttle opening. Idle fuel and some air is supplied to the engine below the throttle plate. The other carb may be doing all the air/fuel delivery at idle. Are the idle speed screws adjusted the same amount?

If air was bypassing the throttle plate, the idle and engine speed would increase (not controlled). Sounds like the engine idles fine.

Begin with one crossbar link disconnected and with a Synchrometer to compare relative air flow into the carbs. Your setup instructions should have some description on this procedure.

Hope this helps,
Sherwood

[Mo_Gearhead]

QUOTE: "What is the idea with this question?'
__________________

IE: Vacuum inlets.

Well, I was trying to find another source for air to be entering the carb. other than the tops.

Sherwood has a good plan. Unhook carb. links, use the Synchrometer to try and establish what's happening. It may seem to idle fairly smoothly even if only one bank (2-3-4) is active (at idle).

[Antal]

Thanks for the tip. I am not sure however if this is the issue as carb 1-2-3 doesn't take that much air in at 3000RPM either but I will try it this weekend. I will post the results.

[Mo_Gearhead]

Edit to my previous post.

I mistakenly referred to the vacuum inlets in the carb. when they are in fact in the manifold (at least mine are). Just wanted to be certain that they were not your source of the air leak.

[Antal]

Weekend update. I took off the inlet manifold and replaced the gaskets. I also replaced the gaskets between intake funnel and base. Air is now being sucked in from the top so this must have been the issue. Synchronising the air intake is however still an issue. I am considering leaving this up to a professional. Thanks all for your contributions.

[70SWT]

Have you purchased one of these?

They are available for about $25 through most VW parts sites, probably here at Pelican as well.

[Antal]

Not this specific one but a more simple one so without the scale. Would this one be better?
Pelican offers one for $53.

[jluetjen]

When you washed the bodies in the dishwasher, what if anything did you use for detergent? My experience is that using that cleaning method is a great way to start oxidation.

[Antal]

I used the regular dishwasher stuff so I hope you are wrong. Time will tell.