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Vent holes in carburettor


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Could somebody please enlighten me on the purpose of these two holes which are on these 175 please?   So not the four mounting holes but the other two which are opposite each other..

 

Secondly the gaskets ....if I put the gaskets on as shown in the picture with 2 x carbs, that then blocks one of the said holes?16338577774864989938202084209186.thumb.jpg.47114e29d27b1e6a1b17aded6a4923d1.jpg

16338575860165245514801919808751.jpg

Edited by AarhusTr6
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2 minutes ago, harlequin said:

Richard

The brown book page 19.15.11C shows the lower hole just behind the bypass to be the one that is open

George 

Hi George

That makes sense, as I took the TBV off today and can see that holes channels to the TBV hole (which I am planning to blank off to help my high tickover).  Any ideas what the other hole is?  

Richard

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39 minutes ago, harlequin said:

Hi Richard

No sorry I can only guess its a drilling used in the manufacture of the carb.

If Poolboy comes along he will be able to give you a proper answer

George 

Well its so far seems to have no importance, and now I know how I fit the gaskets, which I am praying helps my over high idle!

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On 10/10/2021 at 5:20 PM, harlequin said:

Don't  forget the nylon spacer.

George 

Yes, actually had the wrong ones, the ones I had on kind of narrowed on the middle, so ordered some new square ones

Richard

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Well - - I figure I have done it - the high tickover!

Is has taken me so long and so much reading, but when I got the brand new rebuilt carbs back, I had nothing but high RPM no matter what I did but did really believe issue had to be a leak somewhere.  So I did, this weekend the following:

Blanked off the throttle bypass valve with a thin sheet of metal

New spacers from carb to manifold - one I got before curved in middle, new ones are totally square

New gaskets on both sides of spacer

 

Slowly and carefully I put it all back together and RPM is now 600-800!    

For some reason this took months to figure, so missed a lot of driving but satisfaction on getting it sorted was immense.  Thanks to all who helped,

Richard

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I think the curved spacers were the biggest culprit as they would have been letting in excess air.

Stuart.

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Little late getting here....that hole, I'd call it a 'blind hole'...it's about 2 inches deep with no opening that I know of...If you put a vacuum on it, the vacuum holds.

Glad you did what you did, Richard

 Blanking off the TBV is a fairly common practice...even if it's properly adjusted to open only during engine braking, it's diaphragm will eventually stiffen up, split or crack and mess up your idle.

I don't care much for keeping the Temperature Compensators active or enabled either

 

 

 

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