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Pinto Idle


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I have just about finished my Robin Hood but there seems to be a problem with the idle. After a couple of minutes it starts going lumpy and cuts out. It keeps cutting out if I don't hold the throttle open slightly.


It is a 2.0l Pinto with a Weber 30/34 DFTH. I noticed there is a pipe coming from the carb that looks like a breather (black and red). The problem stopped when I sealed the end of this pipe. This may be a stupid question but, does anyone know what it is for? Is it originally from the air cleaner?





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Kick down control to the filter?

Controlled input to air filter from hot round the exhaust or cold air from in front of the rad for more power.

I might have this wrong as it is a long time ago when I worked on these.

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Guest MrToad

Happy New Year and Hi,

From the looks of your photo this is a breather from the sump of the engine. This position matches the system on my engine and runs through a small filter/valve on the side of the cylinder block. I have mine plumbed into a separator taking the breathers from 3 points (2 x sump + 1 rocker box) with a drain into a catch tank. There is a difference with the Cosworth set up on mine but the cylinder block and feeds are from the Pinto plus I am running a non standard air filter.

My understanding is that the breathers must be clear to prevent excessive back pressure in engine(excessive back pressure can cause seals to fail) they do require however valving to allow just enough back pressure to be maintained, otherwise you will loose the vacuum hoses integrity.

This sounds to be the most likely answer as with carbs they will not have variable control on the mixture which seems to be whats happening as the carb will involve over rich on start(choke/auto choke) then cut down to normal mixture, which will not be enough to run the engine with an air leak(but compensated for when choke active or your input of increased throttle).

The hose would be best if you could feed it back into the induction line so that any fumes from the sump are burnt off going back through the engine and seal at he same time.

Have a great 2019



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  • 2 weeks later...

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