Boxer 4 SU carb setup advice on a 3.9

V8James · Post by **V8James** » Mon Apr 26, 2010 9:36 pm

Hi all
Ive picked up a boxer 4 SU carb setup complete a while ago for my 3.9 land rover trialler
Just wondering if anyone has any base carb settings i should work from?

They came of a lightly played with 4.6 off road racer so will be too rich + i just need i rough base setting to work from

Cheers all
James

kiwicar · Post by **kiwicar** » Wed Apr 28, 2010 9:51 am

The way to start withthis set up is with watever you have to get it running, having said that the SU design means it will give an air fuel ratio in the 12.5 to 15:1 pretty much regardless so you should be OK there. next stage is to get full range of lift on the pistons, this is your spring selection above the piston, 3 of them will be the same spring, the fourth (the one seeing two cylinders fireing 90 degrees apart will need a stiffer spring (do all this with the dashpots out). next stage is dash pot oil, again 3 will be the same, probably 10/40 or 20/50 to get everything stable and picking up well, the fourth will need 20/ 50 or even 80 of 90 weight gearbox oil to get it to lift at the same rate as the others. Once you have this sorted you can start looking at needles.
Best regards
Mike

CastleMGBV8 · Post by **CastleMGBV8** » Wed Apr 28, 2010 11:35 am

Mike,

The carb with the stiffer spring and thicker oil would be the one feeding cylinders 5 & 7 I take it?

Kevin.

Eliot · Post by **Eliot** » Wed Apr 28, 2010 1:01 pm

you may find the following article by the creater of the boxer manifold interesting:
http://www.mez.co.uk/ms12.html#boxer

kiwicar · Post by **kiwicar** » Wed Apr 28, 2010 4:10 pm

Hi Kevin
If it is 5 & 7 that fire 90 degrees apart drawing from the same runner then that carb is the one I chopped off a bit of the spring on and stretched it (quite a bit) to get it to lift with the others.
Best regards
Mike