Rebuild 40IDA 3C - Need some advice
 

Hi.

I have a '75 2.7 911. It has been built with Electromotive and 40IDA 3C Weber's. The car has been running fine until some weeks ago. It then started to have trouble between 1500-3000rpm. above and below was fine.

I have dismounted the weber's and done a rebuild after cleaning all the parts with a ultrasonic machine. I have mounted the carbs back on the car and done the adjustment. I have used the STE to adjust the airflow so it is aligned first pr side, then all together. The car is running fine on idle with stable rpm. So far so good.

But then starts the trouble.

1. Adjusting the mix on the left side, I get a raise and lowering of rpm with adjustments of the mix needle. and if i turn it all the way in the engine almost stalls. On the right side I can't get a change when adjusting... why? I have set them to the same count as on the left and it sounds good, but don't know if it is optimal.

2. I also noticed, that if I manually operate the acceleration pump on the left side the engine dies. If I do this on the right side, nothing happens. What is the correct thing here?

3. when reving the engine it rev's fine, but when I try to drive the car it feels powerless and it won't rev over 3-4000 when not driving downhill.

The only parts that have been changed is the gaskets and the needle valves. The car now starts easy, goes steady on idle and revs fine when not driving. The only thing I notice is that the sound feels a bit more "hollow" then before. Could it be pulling false air somewhere?

I am helping a friend with his 1977 911S w/2.7 and Webers, with pertronix ignitor and Permatune......same issues. I look forward to reviewing the replies to your question.

regards,
al

Hmm.. It was quiet. I'm having a look at the car again today. Hope to find something.

Paul Abbott is the weber guru. Could have found that out with a search. He is 1QuickS on pelican and his outfit is performance oriented. He is extremely knowledgeable and helpful.

Look up Paul's phone number and call him. He is a real nice guy and very helpful.

usually a 'no rpm change' when adjusting points to dirty idle jets. might be worth pulling them out again to visually confirm they're perfectly clear.

one thing you didn't mention that I ran into when tuning my webers is the float level. the right carb could be too low. finally, you may have damaged the diaphragm in the right accel pump.

+1 on float level.

Also, check your pertronix alignment. I had one that got out align and too close to the pick-up. That caused an RPM problem and ultimately the unit failed, actually wore a grove in the unit.

I fixed it today! Kind of embarrassing, but I'll put it on that it's my first time, I was working almost in the dark and was in a hurry. Not a good combo. :p

Opened up the middle bolt on the float bowl... nothing. :confused:
On the other side even an untightening of the same bolt gave me petrol. :-)
I opened up the dry weber, and the floater was put in the wrong way!! :mad:
I turned this around and put it back together. Now things started to happen. :D

But I also had issues with the new outer black gaskets on the acceleration pump. I had to switch this back to the old ones as the left one was leaking and the right one made just a strange sound. When the old one was mounted I now could hear the petrol beeing pumped when operated.

Adjusted everything to lean beast and now the car goes like ....!!! :D It is butter smooth from 700-7000rpm, silky smooth sound (less "hard" noice), and no lag on trottle. :D:D:D

glad you sorted it out! i think it's impossible not to mix something up your first time.

for me it was a stuck float that sent fuel spraying everywhere like old faithful..

Glad to hear the problem is resolved, good work!

I see many Webers and about 90% of them have floats that have not been adjusted to be at the correct height. It is important to set float heights since the main circuit timing is directly affected by fuel level in the float bowls. Also, only about 5% of fuel floats I have seen have factory geometry so using a "standard" gasket or shim pack thickness will not set float levels correctly.

Get a float level vial and adjust float levels after running your engine to establish a running fuel level height. I provide a procedure at the top of this web page: Performance Oriented

Where can I buy this?

Here:

Porsche 911 (1965-1973) - Carburetors - Page 1

Paul, thank you for your write ups and contributions! they were essential in helping me set up my carbs!