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Esso petrol contaminated with water or stale petrol

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K2-K6:

--- Quote from: McCabe-Thiele (Ted) on October 10, 2023, 10:23:57 AM ---Sounds unusual but our old 1275 S had inch and a half SU's that I changed to inch and a half Stromberg's as they were more responsive and easier to get the mixture right iirc it was an Alexander conversion.

--- End quote ---

My feeling is that, historically, people went the wrong way with SU in how they work. I trim them with oil viscosity in the damper tube to get acceleration mixture advantageous to response, when many focused on getting the main slide as far open as possible, which drives them lean just when they dont need it.
Thicker oil viscosity delays the slide lift, increasing vacuum, making them richer for transient throttle opening....really livens up the torque on them, but without having to go richer on overall jetting.
They also need very, very short wide radius intake profile and never "trumpet" type bellmouth arrangement, think the Rover TC setup does do this as std, as they flow as much air as next bore size up like this, in comparison to long intake equivalent. 

There was very good description in CCC mag years ago researchiing these flow characteristics.

McCabe-Thiele (Ted):
My best mate & I who had a similar Mini tried all sorts, 3 in1 oil, brake fluid, Redex UCL etc in the end we used Duckhams 20/50 green  engine oil.

Happy days back then. ;D ;D ;D

PICT0340 by Macabe Thiele, on Flickr

K2-K6:
EP 90 really makes them "jump" it's like having an accelerator pump system, ran it for different setup on a dyno with V8 Rover, A/F ratio checking to see what it was doing.

You can hear when they go lean (most carb really) but the sound really changes on SU as you can hear it sucking but no pace to pickup, that completely disappeared running high viscosity.

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