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MG Midget and Sprite Technical - with or without vacuum?

When changing from stock to electronic ignition, does it matter if the new unit has vacuum or not? The old one is a vacuum unit, but since i've fitted a weber i have no place to connect it to anyway. Enlighten me!

Alex
Alexander Sorby Wigstrom

good afternoon
I put a 45dcoe on my 1500 and there was no place for a vacuum pipe. I looked into this further a found that the 45dcoe is fine vacuum-less.. I bought an accuspark non vacuum distributor and hey presto..all is good
rgds tony
a boyle

My understanding is ...the vacume is there primarly for better fuel economy

Edis ignition systems dont have vacume ither, and look how reliable and dead on accurate they are.
Prop and the Blackhole Midget

Alright, No vac it is then!

Thanks guys!
Alexander Sorby Wigstrom

Props EDIS ignition comment is a red herring as while the EDIS module doesn't have vacuum input it does have ECU input for advance control. The EDIS unit can operate without ECU input for a fixed advance (limp mode?) but the normal operation is for it to have an advance input from the ECU to control the spark advance and so the ECU would have the mapping information and be able to take load information in the way of vacuum or throttle position.

I operated my sprite 1420 without a vacuum advance and used a Dellorto 40 DHLA but it should give better part throttle economy with an appropriate vacuum advance.

BTW one of the 5 40 DHLAs I have does have a vacuum advance take-off port fitted behind the throttle plate. I have 3 pairs of 40 DHLA and the newest seem the have a place for the take-off in the casting, one is fitted and the other undrilled with no pipe fitted.
David Billington

David - How did you find the 40 sized Dellorto? I usually read recommendations that suggest 45 is the one to go for, although when you read the calcs for suggested choke sizes they certainly appear to be in the 40- bodied range for the output I'm hoping for?
I ask because I have a couple of 40DHLAs, and a 1360 project. My Megajolt EDIS could be configured for a TPS or MAP sensor.

Mark
M Crossley

At 1420 CC, Id think a 40 is still to small

How did you get a 1420 cc, im guessing you did a 1360 and then storked the mary funning jesus out of it

Thats a great idea... just drill and install a vacume pipe behind of the butterfly

David, ....the red harring needs some extra butter...hahaha

thanks for the extra insight, I certianly wasnt aware of nor had I thought of that

ive got a partial EDIS kit I want To install on the midget at a later time....so just now into the research of that modification to come...so I probably shouldnt have said anything as I know just enough to confound the most trident of experts

If you think its screwed up, then let me at it...I can screw it up beyound all belief LOL.

Prop
Prop and the Blackhole Midget

Mark,

The 40 DHLA worked fine on the 1420 but I was using a home brew manifold which allowed both chokes to feed both inlets so not the normal configuration. IIRC Contact Developments, the UK Dellorto Consessionaires, knew the type of configuration and advised on jetting and said it wouldn't make the max power of a normal set-up with a 45 but would work well. IIRC it made 85bhp at the wheels. The reason for using the 40 DHLA was that I had 6 acquired at £7.50 each average courtesy of rusty Alfa Romeos and a 45 would cost more than the whole lot even 2nd hand.

Prop,

The 1420 is a 1380 with a 1098 crank. I had a wedged, lightened, tuftrided 1098 crank from a short lived 1215 Imp pistoned engine, 1215 = 1098 overbored with Hillman Imp pistons. Lovely engine and ran very smooth as the Imp pistons are somewhat lighter than the standard 1098 but the engine died prematurely due to an undetected water leak resulting in overheating and cracking the block between 3 and 4.
David Billington

David,

Very cool puzzle....how much differance of rod journal height is there over the 1275 crank....or was the 1098 crank rebuilt with A longer rod journal.

Prop
Prop and the Blackhole Midget

Prop,

Big mains crank so all journals the same size as the 1275 spridget engine. The only bearing alteration was IIRC 0.005" of the back of the thrust bearings to fit. Flywheel was a lightened 948 fitted with a heavy duty 1275 clutch cover.
David Billington

This thread was discussed between 05/09/2013 and 06/09/2013

MG Midget and Sprite Technical index

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