Fitting a pair of Alloy Carburettor Mounts
Posted: Sat Jan 16, 2016 8:31 pm
Like many of you who like me do a search on this forum for any possible tips and shortcuts before they start a project, I have prepared this posting outlining the fitting and the minor problem I had with fitting the excellent club procured alloy carburettor mounts.
They are a work of art although I could not but help smiling to myself and thinking that I paid a similar amount of money for the last complete (but somewhat worse for wear) 1850 Dolomite. It is all relative of course and there is no way that I could fabricate a pair of mounts for what I believe to be a very reasonable amount of money.
I had been watching the cracking worsen on the two original carburettor mounts on my car for some time and wondering just how long they would last before one split open. I ordered a pair from the club stock which arrived very promptly. Jonners commented elsewhere in the thread on alloy mounts that the studs were too long so I shortened the ones which came with mine to an inch and a quarter long overall. Those studs are now marginally shorter than those on the mounts which they replaced but it does allow me to screw all the nuts on excepting the top right hand nut on the rear carburettor, when both carburettors are sitting correctly on the inlet manifold.
I removed the carburettors as an assembly bolted to the back plate of the air cleaner in order to hold all the linkages in their correct relative positions having of course disconnected the throttle and choke cables and the petrol feeds, the vacuum attachment to the distributor and the vacuum (balance?) pipes that pick up the oil breather on the rocker cover. And last but not least, the throttle actuating arm.
I removed the two existing carburettor mounts which were still in one piece, cleaned the faces on both the manifold and the carburettors of any traces of the gaskets and then ran a smear of rubber grease over the O-rings on the alloy mounts before bolting the mounts up and placing the carburettors back on the engine.
I did find that once I had positioned the carburettors back on the manifold that it was easier to remove the air cleaner back plate in order to tighten up the eight nuts holding the carburettors to the mounts.
Following the reconnection of all the attachments and starting the engine, the engine revs rose immediately to over 3000 rpm. I adjusted the two throttle idle adjustment screws but this had no effect at all on the idle speed. It took me some time to figure out the problem and it all became clear when I studied tangocharlie1’s topic “what have I done here”. I have marked one of the photos which he took of his installation which shows the problem which I had and in doing so I have outlined the solution.
There is some subtle difference in the alloy and original mounts for in my case while the centre spring, attached to the throttle actuating arm and which pulls the throttle closed had done just that, however it was still holding the right hand carburettor spindle open slightly.
I loosened the clamping nut off, which allowed the spring attached directly to the right hand carburettor to pull the carburettor butterfly spindle to close up against the idle adjusting screw and then proceeded to follow the instructions given in Jonner’s excellent wiki article on SU Carburettor Tuning and completed the installation.
Robert
They are a work of art although I could not but help smiling to myself and thinking that I paid a similar amount of money for the last complete (but somewhat worse for wear) 1850 Dolomite. It is all relative of course and there is no way that I could fabricate a pair of mounts for what I believe to be a very reasonable amount of money.
I had been watching the cracking worsen on the two original carburettor mounts on my car for some time and wondering just how long they would last before one split open. I ordered a pair from the club stock which arrived very promptly. Jonners commented elsewhere in the thread on alloy mounts that the studs were too long so I shortened the ones which came with mine to an inch and a quarter long overall. Those studs are now marginally shorter than those on the mounts which they replaced but it does allow me to screw all the nuts on excepting the top right hand nut on the rear carburettor, when both carburettors are sitting correctly on the inlet manifold.
I removed the carburettors as an assembly bolted to the back plate of the air cleaner in order to hold all the linkages in their correct relative positions having of course disconnected the throttle and choke cables and the petrol feeds, the vacuum attachment to the distributor and the vacuum (balance?) pipes that pick up the oil breather on the rocker cover. And last but not least, the throttle actuating arm.
I removed the two existing carburettor mounts which were still in one piece, cleaned the faces on both the manifold and the carburettors of any traces of the gaskets and then ran a smear of rubber grease over the O-rings on the alloy mounts before bolting the mounts up and placing the carburettors back on the engine.
I did find that once I had positioned the carburettors back on the manifold that it was easier to remove the air cleaner back plate in order to tighten up the eight nuts holding the carburettors to the mounts.
Following the reconnection of all the attachments and starting the engine, the engine revs rose immediately to over 3000 rpm. I adjusted the two throttle idle adjustment screws but this had no effect at all on the idle speed. It took me some time to figure out the problem and it all became clear when I studied tangocharlie1’s topic “what have I done here”. I have marked one of the photos which he took of his installation which shows the problem which I had and in doing so I have outlined the solution.
There is some subtle difference in the alloy and original mounts for in my case while the centre spring, attached to the throttle actuating arm and which pulls the throttle closed had done just that, however it was still holding the right hand carburettor spindle open slightly.
I loosened the clamping nut off, which allowed the spring attached directly to the right hand carburettor to pull the carburettor butterfly spindle to close up against the idle adjusting screw and then proceeded to follow the instructions given in Jonner’s excellent wiki article on SU Carburettor Tuning and completed the installation.
Robert
