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Old 02-18-2016, 03:20 PM   #11 (permalink)
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Injection or a smaller carb? I have a SU HS4 sitting here that came with it

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Old 02-18-2016, 04:00 PM   #12 (permalink)
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Sweet Aunt Jemima, I have no idea. Never ever turned a wrench on a Mini, or any British car for that matter.

I bet it'd be a lot of fun though.
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Old 02-19-2016, 02:20 PM   #13 (permalink)
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Been researching the carbs, thisis what I got:

Weber 32/36 - 320 cfm, 3-3.5 fuel psi

Su HS4 - 133 cfm, 2-3 fuel psi

The 1275 just needs just 134 cfm at 85% VE!
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Old 02-19-2016, 03:46 PM   #14 (permalink)
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The later minis could come fuel injected. Would it make sense to swap EFI on it?
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Old 02-19-2016, 08:12 PM   #15 (permalink)
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Well, based on those numbers it looks pretty clear to me that you're over-carbed. You might be getting poor fuel atomization/fuel burn due to low flow rates.

Have you had it smogged? That could tell you more.
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Old 02-19-2016, 10:08 PM   #16 (permalink)
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No smog yet, need to go to the next city over as we don't have it here. Is the over carb that bad for milage? I'm new to carbs still too, just picking up what I'm finding.
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Old 02-19-2016, 11:12 PM   #17 (permalink)
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If you get the SU working right it will beat the Weber easily. The first 240Zs with dual SU type carbs would do close to 28 highway. They ran lean enough that they were undrivable without manifold preheating under 55 degrees.

That "told" you they were set up about perfect.

Half the carb 1 for half the displacement no toilet accelerator pump, good old variable venturi with single point fuel delivery.

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Old 02-20-2016, 02:20 AM   #18 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post
If you get the SU working right it will beat the Weber easily. The first 240Zs with dual SU type carbs would do close to 28 highway. They ran lean enough that they were undrivable without manifold preheating under 55 degrees.

That "told" you they were set up about perfect.

Half the carb 1 for half the displacement no toilet accelerator pump, good old variable venturi with single point fuel delivery.

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How much gain are we looking at with a SU? That would be a dream come true to be up near or at 40 mpg.
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Old 02-20-2016, 02:24 AM   #19 (permalink)
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Quote:
Originally Posted by darcane View Post
The later minis could come fuel injected. Would it make sense to swap EFI on it?
It would make sense, but the kit for injection is $2k before getting the ecu tuned. Where I'm at now I have no ecu lol
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Old 02-21-2016, 03:53 PM   #20 (permalink)
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Too much carb is pretty bad for mileage, yeah.

If you're running wide open all the time for racing it's less of an issue as the air flow through the carb gets up to useful velocities. But when you're just motoring you need a more modest setup.

With too much carb, you're wasting some of the engine's energy pulling a vacuum against the inside of the throttle butterflies when you're tooling around at lower speeds. The low velocity gives poor fuel atomization (already mentioned) so you have to run rich just to get enough fuel to burn in the cylinder to keep you going down the road. It's a cascade of problems that all stem from too much carb and result in bad fuel economy. The rich condition might not be as bad as all that if the carb is set up carefully, but I bet it's a little smoggy when it's running.

You watch. You put the SU in and your torque peak should move pretty far down the rev band where you can use it more conveniently in daily driving. If the Weber was set up correctly you're probably going to feel the loss of some top end power, but the engine should be a lot more drivable. If you've been running smoky, switching in the right carb should reduce that.

For what it's worth, the Weber 32/36 is a recommended aftermarket replacement for my truck, which has almost literally twice the displacement your engine has. If it's a good carb for an engine that size, then you have to be either revving the nuts off a smaller one all the time to make use of the Weber's capacity, or else it's just more than a daily driver can use effectively.

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