psears

Hello,

I have a new Weber 40-IDA carburator set-up on my 1981 911SC, and I love the improvement over the stock CIS system-except for the start up. This kit didn't come with any provision for a manual choke lever. The side-draft Webers on my old 240Z had one, but the people who sold me this, as well as my mechanic, said they don't know of any for this particular application. Do any of you know how I can solve this as I hate having to sit in my car reving my engine for 5 minutes!?

Thanks!
psears@austin.rr.com

Howard

There is no choke set-up for the IDA's, if you have difficulty starting it's most likely a problem with the idle circuit. I have 40's on a 3.0 and 46's on a 3.4 race motor and both start right away with 3 pumps of the throttle. You may look at the accelerator pump for a steady and forceful stream in the venturi from the pump jets(it looks like a beak).Also, inside the fuel bowl there is a check valve that prohibits fuel from surging back into the bowl,on the 40's there is no exhaust(a small pin hole on the valve). Make sure your's are correct, otherwise you won't be delivering enough fuel at start-up and accelerating. Last, check the accelerator pump bladder, they tear easily, and/ or, could be installed incorrectly. You can get any Weber parts you need at www.webercarburetors.com

psears

Howard,
What do you mean by the idle circuit?(guess I'll need to buy a Weber book)
With a few stomps of the gas pedal mine also starts up like yours, but it's the low idle and stumbling during warm-up AFTER starting that is a pain. The only way I've ever known to alleviate this problem in a cold engine is to richen the mixture, which usually means a choke (manual or automatic)until the engine reaches operating temperature.

Without this feature, isn't it against the "laws of physics" for the carbs to work normally at all temps?!

Thanks!

Howard

It could be one of several adjustments you can make. And ,yes, you should pick-up a Weber book, you should know the proper procedure for initial settings. The idle jets are installed behind (3) slotted screws near the top of the carbs just below the gasket line for the cover on the outside of the carb (valve cover side)when you remove the screw there should be an "o" ring near the head, inserted into this screw is the idle jet,it just slips in. On the side of the jet should be a number,anywhere from 45 to 70,try different jets ,the smaller the number, the LEANER the mixture, up to 2000 rpm's or so then the progression circuit takes over. If it stumbles up to that RPM it's most likely the Idle circuit. I'll scan a few pages from my book and e-mail it to you.

john walkers workshop

you will probably need a .60 idle jet to get a decent warmup period. any larger and you will constantly foul plugs.