Boxer 4 su carb setup, any good?

V8James · Post by **V8James** » Thu Oct 08, 2009 6:35 pm

Hi all
Ive got a genuine Boxer 4 SU complete carb setup, just wonderin how good they actually are
If they go on an engine it will be a 3.9, ive head they are not great but can give very good increase in torque

Cheers
James

Tricky · Post by **Tricky** » Thu Oct 08, 2009 7:31 pm

They do give better torque and power on the plus side

On the bad side there a pain to balance up and keep in tune

Only what i think

kiwicar · Post by **kiwicar** » Fri Oct 09, 2009 12:38 pm

also very effective on a 4x4 as they opperate over a wide range of vehicle angles. Depends what they are going on if it is a car used every day then they are a pain to keep in ballance, if it is low use fun car then you can live with it.
Initial set up is a bit tricky too as you have to get the pistons in the carbs lifting together, easy on three of them but the 4th carb sees two induction pulses 90 degrees after each other, you need to get this one ballanced to the other three using the spring above the piston and the oil in the dash pot once you are sure you have the throttle in the carb opening correctly.
Mike

ppyvabw · Post by **ppyvabw** » Fri Oct 09, 2009 12:42 pm

Tricky wrote:They do give better torque and power on the plus side
On the bad side there a pain to balance up and keep in tune

Only what i think

Not much worse than tri carb set ups on jags and what have ya and they are perfectly servicable.

CastleMGBV8 · Post by **CastleMGBV8** » Fri Oct 09, 2009 1:26 pm

James,

What mike said basically, that 4th carb is very difficult to get right, I know someone who has this set up and he has never got it to run properly, how much of that is down to lack of knowledge or design issues I dont know.

I did once come a cross a set up for the carb that feeds the seqeuential cylinders and as Mike said it needs a complete different set up to the other three.

If you do a web search on 4 SU Boxer manifold you might get lucky.

Kevin

kiwicar · Post by **kiwicar** » Fri Oct 09, 2009 1:48 pm

On my set up when I had these I had the throttles set up so that there was only one cross linkage, the second two throttles were driven off the carb by its side not off a second cross linkage (I hope this makes sence) when I did this it kept in tune much better, also you could be certain carb 4 was opening the same as carb 2 all the time, this made setting up much easier as it just became a matter of finding a spring of the right rate (select a spring and tweek with a pair of side cutters) and preload (stretch/ compress the thing). I think my set up ended up being a spring 1 heavier than the other three with about 1/2 a coil cut off it and stretched to be about 2" longer running hypoid 90 in the dashpot with 10/40 in the other three I remember I radiused the leading edge of the pistons on all 4 carbs, this had the effect of slightly reducing lift of the piston at very light throttle (but makes it richen out at full throttle).
It did give an improvment in fuel economy (about 2.5 MPG on a 3.5 RR) against the 2 carb manifold.
Mike

chuggernought · Post by **chuggernought** » Wed Oct 14, 2009 4:17 pm

i have this setup on my landy racer, and it goes like hot snot and sounds the biz. (4 inch tail pipes up the back of the cab!

) hav'nt messed with them yet they were pretty much spot on "from the box" forgive my ignorance but what numbering do you give each carb, alright saying number 4 needs a different spring e.t.c but which one is number 4?

Eliot · Post by **Eliot** » Wed Oct 14, 2009 7:59 pm

Lol
Another RIP product that claims to match fuel injection....
Why not just get fuel injection!

Its a bit like the Golf advert isn' it..

Wotland · Post by **Wotland** » Thu Oct 15, 2009 8:02 am

Eliot wrote:Lol
Another RIP product that claims to match fuel injection....
Why not just get fuel injection!

Its a bit like the Golf advert isn' it..

Again an great brainwave of Mr Crane.

kiwicar · Post by **kiwicar** » Thu Oct 15, 2009 10:42 am

Carb 4 does the cylinders 5 and 7 (the two adjecent cylinders that fire 90 degrees part) I supose it could be carb 3, however the importent thing is that it has both cylinders it feeds firing 90 degrees apart.
For referance the firing order is 1-8-4-3-6-5-7-2 .
Mike

chuggernought · Post by **chuggernought** » Thu Oct 15, 2009 1:15 pm

cheers for that kiwicar, difficult to get info on them.

Eliot wrote:Lol
Another RIP product that claims to match fuel injection....
Why not just get fuel injection!

Its a bit like the Golf advert isn' it..

why on earth would i want injection? nothing but trouble, expensive, when it goes wrong you have no chance of getting home, its thirsty and it looks crap under the bonnet!

keep it simple and reliable

with carbs its cheap, simple to setup and tune, simple to maintain, if it does go wrong you can tell by looking at it rather than messin about with laptops, its rarely enough to stop your journey and you can fix it at the roadside, parts are so cheap you can mess with it and not worry about the cost of jiggering it, they are more economical and it looks the nuts under the bonnet and sounds the nuts!
when i open a bonnet i want to see the engine not a pile of pipes wiring and plenum!

as a former professional mechanic i believe the world went mad when it started putting cars in the hands of computers. carbs are not hard to set up its just everyones forgotten how!

remember just cause its old doesn't mean it aint any good, look at raquel welch and carol vorderman

!!

nice dakar by the way, seen it at a few shows, building one for the wife at the mo, with a 4 barrel edelbrock of course

Eliot · Post by **Eliot** » Sat Oct 17, 2009 8:09 am

The big difference with megasquirt and similar, is that you actually learn exactly how it works. You understand each and every component and its not expensive when it goes wrong because a) it never goes wrong and b)no single component is more than a few pounds.
"getting your laptop out" allows you to get a full insight into whats happening and allows you to fault find. Even if you cant spot the fault, you can post a datalog up and thousands of people from around the world are able to look at the problem and assist.
I have a spare ECU, spare edis module and spare coil pack - so I can swap out the entire system quicker than it takes to unbolt one carb.

unstable load · Post by **unstable load** » Sat Oct 17, 2009 9:23 am

They are rubbish!!

Put them in a box, ship them to me and I will dispose of them as required!!

chuggernought · Post by **chuggernought** » Mon Oct 19, 2009 10:30 am

once had an "unstable" moment and looked at megasquirt for the wifes 3.9 disco, cheap it aint! couldn't get all the bits and pieces for much less than £500-600! (unless you guys know anyone that does it cheaper, no doubt you do.)thats before you start trying to make it work. no sorry pair a su carbs on a manifold fer £30, cant compare.
for the record i spent years using laptop based disgnostics on cars, took all the fun out of it.

.
ended up getting out the trade, i'm a mechanic not computer programmer.
the 3.9's on standard lucas efi at the mo but first sign of so much as a hickup and its getting ripped out and a pair of s.u.'s thrown in.
its on lpg most of the time so wouldn't use the fueling side much anyway only ignition side.

ChrisJC · Post by **ChrisJC** » Mon Oct 19, 2009 10:55 am

chuggernought wrote: ended up getting out the trade, i'm a mechanic not computer programmer.
the 3.9's on standard lucas efi at the mo but first sign of so much as a hickup and its getting ripped out and a pair of s.u.'s thrown in.
its on lpg most of the time so wouldn't use the fueling side much anyway only ignition side.

The ECU doesn't have anything to do with the ignition system on the 3.9. You can ditch the ECU and you'll still get a spark.

I'm with Eliot on fuel injection (provided it's not on a Landie that lives in mud slurry all the time)

Chris.