Stuck secondary throttle butterfly?

Post by **Scarabrae** » 31 Dec 2005 06:18 am

Hi

While changing the air filter on my 1.7 340 I noticed that while their was petrol being squirted into the secondary throttle when I revved the engine...the butterfly only opened by a tiny fraction to let the neat petrol in. It initially just lay on top of the closed butterfly until I revved a good bit more.

Wondering if this is normal? And if not then this may explain the heavy fuel consumption and the hesitation I experience when I choose to prod the accelerator heavily?

Car has done 60k and is an H reg.

Thanks

Post by **pettaw** » 31 Dec 2005 10:24 am

the secondary throttle only opens when well towards full throttle. This is to save the extra oomph for when you need it. Also it won't open when the choke is on. I wouldn't think it would affect fuel consumption at all really.

Are there any other running problems?

EDIT: I should learn to read posts properly

The hesitation is probably caused by an air leak, or the carb loosening off its base, get an allen key attachment and a torque wrench and tighten the four allen bolts to 14nM torque.

The other possibility is a worn accelerator pump diaphragm, not pumping enough fuel when you hit the gas. You can cure this by buying a rebuild kit from a carburettor specialist.

Post by **fidgad** » 31 Dec 2005 11:39 am

I had this problem recently so changed the top gasket. That stopped it and my consumption improved. IIt showed up originally on a pre-MOT emmission test. Couldn't figure it out until remove aircleaner and peered into orifice. Is it sort of dripping from the pipe that spns the venturi? It took me a while before I realised it must be the gasket.

Post by **foggyjames** » 31 Dec 2005 02:16 pm

Take the filter cover off, push the choke in, and give it full throttle by hand on the carb by moving the linkage. You should (as Andy says) finally see the second throttle move near full throttle.

Yes, it should squirt fuel onto the closed throttle plate...that's the pump jet in action, and just a limitation of the design. A bit daft I know, but that's that.

cheers

James

Post by **Scarabrae** » 31 Dec 2005 09:42 pm

Thanks for your quick responses to my question...the explanations as to when the secondary butterfly should open has been a great help. I will check for air leaks etc.....

Cheers