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SU improvments

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andrew240 Avatar
andrew240 Andrew Herr
MO, USA   USA
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Has anyone here ever went into there SUs and smoothed out some of the leading edges, like right before the needle, with a dremel? I would imagine this would help smooth airflow out a bit.


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aborris Andy Borris
Kent, UK   GBR
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Read the Burgess book for the best way to do this.

AndyB

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GregS Greg S
Brandon, VT, USA   USA
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Post Edited (03-23-05 12:39)



Greg
74.5 B

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Frank Frank Puccio
Bayville, NJ, USA   USA
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Also the book "Tuning the A series Engine" has an excellent section on improving the SU carb.

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Wade Keene Avatar
Homewood, IL, USA   USA
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There's also a book called "rebuilding and improving SUs" or something to that effect by Des Hammill that also does a good job of showing the things that can be done.

Be conservative when/if you round any edges work on the throttle-shafts, etc. If you do too much your carb will flow so well that it won't idle. Note that I said won't idle, not won't idle well, won't idle! Smoothing the bridge - the area where the needle meets the the carb body - is not recommended unless you're racing. Grinding down the throttle shaft at the butterfly is a good mod.

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moreso74 Avatar
moreso74 David Maples
Augusta, Georgia, USA   USA
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Don't touch the Bridge under the needle!!!!!!
That is the base for the venturi. You mess with that and you will have to re-invent the SU.





David

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Hap
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On HS2s and HS4s for racing we thru-bore them, meaning no bridge what so ever, on HS2 you will actually run out of room, meaning a hole in the bottom of the carb you have to epoxy up. However for street cars this would ruin driveabilty, but with race carb nothing but wide open throttle matters. On a street car I would not worry about bridge mods, if I made any mods to a stock carb for the street I would think about beveling the slide so the square leading and trailing edge is nicely radiused towards the opening front and rear. There are a good many books on SU carbs that was mentioned above, also consider getting on chassis dyno with a air/fuel ratio meter, you might be pleasantly surprised with the gains you can make with stock carbs with the proper needles and jet adjustments.





Hap Waldrop
Acme Speed Shop
Greenville, SC
www.acmespeedshop.com

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Frank Frank Puccio
Bayville, NJ, USA   USA
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I blanked on the author of this and just remembered it is David Vizard. This is an outstanding book....one of the best I have ever purchased and would recommend it as great reading to all MGB owners.

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Gerry Avatar
Gerry Gerry Masterman
Prairieville, LA, USA   USA
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Best thing you can do for your SUs is to leave them alone. They do not need someone trying to re-invent the wheel





Lord, please give me patience because if you give me strength I will have to ask for bail money, too

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