Hi all
Update on my SU carb conversion on my 73 2.0 wagon.
As some of you all may know about a year ago I built a custom manifold to fit 2 SU HIF 4 1 1/2" carburetors from a 72 mgb onto my 2.0 in a 72 wagon.
I recently replaced the original engine which was running well but had low compression with a stock rebiluilt 2.0 only mod was a .040 mill on the head to up the compression.
I have an adjustable cam pulley, also recurved the distributor and can adjust the carb fuel mixture.
The engine ran really strong and pulled really hard up to 6000 but i was having some difficulty getting the proper settings with 3 variables.
So i dug out the factory holly webber 2500 32/36 and decided to use it to get basic settings.
After driving with bothe the SU and 32/36 carbs i have some observances.
The linkages on the 32/36 open the secondary really late at about 3/4 throttle so i modded the linkage with a wire loop to open the secondary at about 1/2 throttle... big improvement.
The SUs flow.a LOT of air.. BUT with air comes fuel
With the new engine quickly revving to 6000 plus rpm fuel milage dropped from 16-18 with old engine to about 12 with new engine
As stated above the rebuilt factory engine with pulled like a scalded cat from 2000 to past 6000
Same engine with 2 SU carbs at about 1/2 throttle (never pushed it past 3/4 throttle because revs got too high) made more power than stock 32/36 at full throttle (primary and secondary both full open).
Throttle response is a LOT more instantanious with SU sidedrafts.
32/36 seems to flow about half as much air as a pair of 1 1/2 inch SU carbs.
Making power requires more fuel but i think i need to redesign the manifold because an MGB 1800 engine with the same carbs and compression will get 18-23 mpg.
I suspect the problem is that i was getting fuel drop in the plenum 9f the manifold i built.
Am redesigning the new manifold with no plenum and runners directly from.carbs to intake.ports.
Will follow up with report about mileage with stock 32/36 carb and progress with new manifold for the webbers.