Carb and camshaft issue, advice

[flash951]

Porsche 911T targa 1971, 2.7L (original 1975 151HP engine) with Weber IDAP40.
Idle jets .60, the rest i don't now.

The carbs runs way to rich below 3000 rpm, and the engine only pulled out 141 HP at the dyno.

I heard from a friend that I needed to change camshafts to make the engine run well with Weber. I have now installed the 2.7L S cams (1975).

Additional info:
I have the 11 blade fan and seperate heat exchangers. However I have an unoriginal very small muffler and the pipes get into 1 before the silencer. The sound is loud and awfull.

I have ordered an 2 in 1 out sport muffler and are waiting for that before I pay for new carb adjustment.

Questions:
1. What jets and venturis should I use with this setup?
2. Was the choice of Cams good? The rest of the engine is very original.

I hope for answer, help.

[Steve@Rennsport]

Hi,

Those idle jets are too large for your 2.7, but you really must open the carbs and find out what main jets, emulsion tubes, main venturies, and air corrector jets you have.

The 2.7S, 175HP version had larger intake runners, airbox, CIS S cams, 8.5:1 pistons, and a totally different exhaust system to make that power. The latter requires a dual-inlet muffler of some kind. Your sport muffler will help. You should see if you have the 150 HP, 32mm intake ports or the later 35mm intake ports.

Those 2.7 CIS cams are OK, but are best matched to the later 2.7 airbox and ruynners, if you have the larger port heads. If you have the small-port stuff, the stock cams make a lot of torque.

Once you know precisely what parts are in your carbs, one can proceed from there. Jetting and configuration depends a lot on what heads you have.

[flash951]

Thank you very much.

1. Can you please give me even more details on each subject you mention, it's very interessting? I'm a newbee at 911.

2. Do I need to remove the carbs from the engine to take it apart in order to check the venturi size and so on?

The carbs was running good over 3000 rpm according to the workshop that "adjusted" the carb the first time, they used dyno and lambda. And told me it was running bad below probably due to worn out idle jets. I think the only thing they did for all that money and 6 weeks with the car away, was to adjust a little on the mixture screw.

I have the -75 151HP 2.7L engine, so i understand I will end up with a torque engine rather than a high HP and revvy engine. TO BAD!

1. How will the engine perform when inserting the original 151HP cams?
2. Is there something not to expensive I can do to change that?

Thanks in advance.

[Steve@Rennsport]

I'd kindly suggest investing a little $$ in some books. Start with Bruce Anderson's 911 Performance Handbook, Paul Frere's 911 Story, and get Wayne Dempsey's two books to round things out. This should educate you on these cars.

Carbs do not need to be removed; all of the jets are externally removable. Get the Hayne's Weber manual and study the chapter on the IDA 3C carbs.

Idle jets do not "wear out". If someone reamed them bigger, thats a mechanical issue, but they only pass fuel so they last forever unless one tries to modify them instead of buying different ones.

The engine can perform very well depending on how well everything is set up & adjusted. The original 150 HP cams make a torque monster.

[flash951]

Thank you very much. He thought the idle jets was screwed to hard and in that way the hole was miss-shaped and that was the cause. I have now ordered carb adjustment in a different shop that I am sure will make good adjustment and make everything fit from bottom.


I have the original 150HP cams (someone told me those would not run well with carbs)
I have therefor now inserted the 2.7L S cams (CIS)

What will the difference become?
What I really want is a high RPM and HP engine, is there a easy/not expensive way?
I dont want it to end up feeling like a diesel engine equiped car.

[flash951]

Is it a good idea to machine/port the heads to S-specs? What is the cost?

[Steve@Rennsport]

I would measure them first to see if they have 35mm ports.