Carburettor butterflies

[eworpe]

Hi Norman, If the carb. bodies have been bored out for the butterfly spindle-bushes and the bushes have not been pressed far enough in to be flush with the internal bore, then air can flow past the butterfly-bush interface, around the spindle and cause the high tick-overspeed. Just a thought. Regards, Eric. ________________________________________ From: Norman Verona norman@frenchblat.com [mg-tabc] [mg-tabc- Peter, there are no airleaks and the butterfies are closing fully. The problem is the bodies are warped and air is paasing the butterflies at the sides. The top and bottom are fully closed

[joecurto@aol.com]

Here is what happens to TC  and other pre-war type bodies, the original material was a soft zinc alloy ( Mazak?) over the years when installing the carbs mechanics/owners tighten the upper bolt first this tightens the top of the flange and crushes the gasket. BUT this also lifts the lower portion of the flange away from the manifold. now installer goes underneath and tightens the lower bolt. this over time bows the flange and distorts the bore of the carb and also in this material you see what look like warts in the casting . , the fix is machining the flange flat and boring out the throat , I have recently acquired a  official SU publication where they talk about fitting an oversize butterfly , also there have been fellows who sleeve the bore back to standard.     While I have never seen anything written as to the materials SU used in their bodies , I have seen Bronze, aluminum alloy, Zinc and maybe others on pre-war and just post war . They also had some castings with thicker flanges . It appears that post war around 1952 they settled on the aluminum like used on MGTF,  there appears to have been an effort on their part to standardize the castings , they went to light alloy pistons with springs etc. Joe Curto 718-762-7878 www.joecurto.com -----Original Message----- From: Norman Verona norman@frenchblat.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> To: Peter Cole pcoleuk@gmail.com> Cc: Trevor Burnett trevor@safxmarine.co.za>; Rothgene RothGene@msn.com>; MG-TABC List mg-tabc@yahoogroups.com> Sent: Fri, Nov 24, 2017 10:01 am Subject: Re: [mg-tabc] Carburettor butterflies   Peter, there are no airleaks and the butterfies are closing fully. The problem is the bodies are warped and air is paasing the butterflies at the sides. The top and bottom are fully closed

On 24 Nov 2017, at 12:19, "Peter Cole pcoleuk@gmail.com [mg-tabc]" mg-tabc-noreply@yahoogroups.com> wrote:   Norman, We seem to be discussing two different problems here.  If the butterflies don't close properly then the car is likely to tick over too fast as you report due, to an excess of fuel and air entering the engine.  If there are any leaks from the spindles, the inlet manifold or due to lack of flatness of the flanges air will certainly be sucked in, but no fuel with it, so the engine will run weak and probably stall. Regards Peter Cole.    On 24 November 2017 at 11:07, 'Norman Verona' norman@frenchblat.com [mg-tabc] mg-tabc-noreply@yahoogroups.com> wrote: [u][/u]   I ve heard that many think the distortion to the flange is from overtightening whereas it s from heat. It happens far less on cars with plastic insulating blocks hence why, after getting my flanges flat (no comments please) I fitted longer studs and plastic blocks as per the MGA.[u][/u][u][/u] [u][/u] [u][/u] [u][/u] [u][/u] [u][/u] [u][/u] [u][/u] [u][/u] [u][/u] [u][/u] [b][i]Norman Verona[u][/u][u][/u][/i][/b] 11 Cherry Close, Royston, South Yorkshire S71 4LZ[u][/u][u][/u] Phone: 0044 (0)1226 728811[u][/u][u][/u] Mob: 0044 (0)741 9905 741[u][/u][u][/u] [b][i]Web: www.frenchblat.com[u][/u][u][/u][/i][/b] [u][/u] [u][/u] [b]From:[/b] mg-tabc@yahoogroups.com [mailto:mg-tabc@yahoogroups. com] [b]On Behalf Of [/b]'Trevor Burnett' trevor@safxmarine.co.za [mg-tabc] [b]Sent:[/b] 24 November 2017 10:40 [b]To:[/b] 'Norman Verona' norman@frenchblat.com>; 'Rothgene' RothGene@msn.com>; mg-tabc@yahoogroups.com [b]Subject:[/b] RE: [mg-tabc] Carburettor butterflies[u][/u][u][/u] [u][/u] [u][/u]   [u][/u][u][/u] Whilst on the discussion, I was given a body with a badly distorted flange, I placed the body in my hydraulic press with light pressure then heated it up with a heat gun slowly applying add. pressure, between the gentle press application and the heat gun and leaving the body to cool down with the applied pressure, the flange only required light lapping to achieve perfect flatness .[u][/u][u][/u]  [u][/u][u][/u] [b]From:[/b] mg-tabc@yahoogroups.com [mailto:mg-tabc@yahoogroups. com] [b]On Behalf Of [/b]'Norman Verona' norman@frenchblat.com [mg-tabc] [b]Sent:[/b] 2017/11/24 11:11 AM [b]To:[/b] 'Rothgene'; mg-tabc@yahoogroups.com [b]Subject:[/b] RE: [mg-tabc] Carburettor butterflies[u][/u][u][/u]  [u][/u][u][/u]   [u][/u][u][/u] There are no leaks at the manifold, the flanges aren t bowed, the butterflies are in the correct way (but weren t fully centralised).[u][/u][u][/u]  [u][/u][u][/u] Just for the record, I started work on January 1st at University Motors and on the Thursday was shown how to overhaul a pair of SU s  on a TC.  That was 1961.However, after all these years of messing about with cars I ve never come across a distorted carb body. As I ve said before, it doesn t matter how much you know, you ll always learn more.[u][/u][u][/u]  [u][/u][u][/u]  [u][/u][u][/u] [b][i]Norman Verona[/i][/b][u][/u][u][/u] 11 Cherry Close, Royston, South Yorkshire S71 4LZ[u][/u][u][/u] Phone: 0044 (0)1226 728811[u][/u][u][/u] Mob: 0044 (0)741 9905 741[u][/u][u][/u] [b][i]Web: www.frenchblat.com[/i][/b][u][/u][u][/u]  [u][/u][u][/u] [b]From:[/b] Rothgene [mailto:RothGene@msn.com] [b]Sent:[/b] 23 November 2017 23:27 [b]To:[/b] mg-tabc@yahoogroups.com; norman@frenchblat.com [b]Subject:[/b] Re: [mg-tabc] Carburettor butterflies[u][/u][u][/u]  [u][/u][u][/u] Check for air leaks at the intake manifold[u][/u][u][/u]  [u][/u][u][/u]  [u][/u][u][/u]  [u][/u][u][/u] [b]From:[/b] mg-tabc@yahoogroups.com mg-tabc@yahoogroups.com> on behalf of norman@frenchblat.com [mg-tabc] mg-tabc-noreply@yahoogroups. com> [b]Sent:[/b] Thursday, November 23, 2017 6:43 PM [b]To:[/b] mg-tabc@yahoogroups.com [b]Subject:[/b] [mg-tabc] Carburettor butterflies [u][/u][u][/u]  [u][/u][u][/u]   [u][/u][u][/u] This isn't my TC but a friends.[u][/u][u][/u]  [u][/u][u][/u] The engine will not run slower than 1500 rpm, even with all adjustments screws fully undone.[u][/u][u][/u]  [u][/u][u][/u] I diagnosed, remotely that the new butterflys fitted by the chap who'd sold him the car wern't centalised. I went there today and took the carbs off. The butterflys weren't correctly centaliseed and the throttles close fully now.[u][/u][u][/u]  [u][/u][u][/u] However I notice that there is a large gap on the sides of the butterfly's and, when refitted, the engine is still running fast. Jerry, the owner says the chap who's been working on says it needs new carbs because the "throats" are worn.[u][/u][u][/u]  [u][/u][u][/u] In over 50 years of working on SU's I've never seen oval throats.[u][/u][u][/u]  [u][/u][u][/u] Any thoughts?[u][/u][u][/u]  [u][/u][u][/u] In the meantime I'm ordering new spindles and butterflys as I suspect the throttle adjusting arms have been drilled in the wrong plalce and the slot in the spindle is too far over one way stopping the butterfly being fitted. To overcome this it looks like he's filed the sides of the butterflies.[u][/u][u][/u] [u][/u][u][/u]

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