AarhusTr6 Posted October 10, 2021 Report Share Posted October 10, 2021 (edited) 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? Edited October 10, 2021 by AarhusTr6 Quote Link to post Share on other sites
harlequin Posted October 10, 2021 Report Share Posted October 10, 2021 Richard The brown book page 19.15.11C shows the lower hole just behind the bypass to be the one that is open George Quote Link to post Share on other sites
AarhusTr6 Posted October 10, 2021 Author Report Share Posted October 10, 2021 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 Quote Link to post Share on other sites
harlequin Posted October 10, 2021 Report Share Posted October 10, 2021 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 Quote Link to post Share on other sites
AarhusTr6 Posted October 10, 2021 Author Report Share Posted October 10, 2021 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! Quote Link to post Share on other sites
harlequin Posted October 10, 2021 Report Share Posted October 10, 2021 2 hours ago, AarhusTr6 said: 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! Don't forget the nylon spacer. George Quote Link to post Share on other sites
AarhusTr6 Posted October 14, 2021 Author Report Share Posted October 14, 2021 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 Quote Link to post Share on other sites
harlequin Posted October 14, 2021 Report Share Posted October 14, 2021 Take your time and check every thing and I am sure you will get to the bottom of your fast tickover, I know when I have found the answer to this sort of problem I ask myself how I 1st missed it, but that's old cars. George Quote Link to post Share on other sites
AarhusTr6 Posted October 17, 2021 Author Report Share Posted October 17, 2021 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 Quote Link to post Share on other sites
stuart Posted October 17, 2021 Report Share Posted October 17, 2021 I think the curved spacers were the biggest culprit as they would have been letting in excess air. Stuart. Quote Link to post Share on other sites
harlequin Posted October 17, 2021 Report Share Posted October 17, 2021 Well done Richard George Quote Link to post Share on other sites
Peter Cobbold Posted October 17, 2021 Report Share Posted October 17, 2021 The top hole probably takes filtered atmospheric air pressure to the underside of the diaphragm. Quote Link to post Share on other sites
poolboy Posted October 19, 2021 Report Share Posted October 19, 2021 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 Quote Link to post Share on other sites
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