su needles for quad carbs

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chuggernought
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su needles for quad carbs

Post by chuggernought »

running my landy hybrid on quad su's with a boxer manifold at the mo, goes like hot snot!
running well but could be better i think.
so question is with 4 carbs would i still fit standard spec twin su needles(bac) or would they need to be a very different profile.
havnt stripped the carbs yet since i got them(they run so leaving them alone for the time being) so dont know which needles are fitted.
going to be playing with the gas anyliser and balencer soon so just getting my head round quad carb setup.



kiwicar
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Post by kiwicar »

Hi
I had a set of these a few years ago on my range rover, and I have posted up some of my experiences with them on here before. I was in tough with the chap who designed the system when I installed mine and found the following.
1/ the carb withtwo cylinders firing one after the other (90 degrees apart) on mine needed a the spring in the piston to be slightly stiffer, this I achieved by cutting a couple of coils off and stretching it
2/ same piston required thicker oil in the dashpot (I used hypoid 90 I think)
3/ again on this carb I ran it "leaner" by putting the needle in the piston on the lower indent (to get over the richening effect of the heavy "pulsing" on this carb.
4/ springs in all 4 SUs were lighter than standard, but I don't remember which ones I used
5/ the needles rcommended had a richer top to them, but I think 3/4 of the reason for this was the K&N filter kit I had.
6/I rounded the leading edge of the piston on each carb, this again richens the top end of the rev range.

To be honest I found the whole set up very difficult to keep running in a good state of tune, if I had new carbs and unworn linkages that would have been better (I modified my carbs eventually to eliminate 1 set of linkages which improved things). The set up was very good off road in that it was pretty well imune to being at odd angles, and pickup was good but I felt it would have been better with more development. Maybe bigger ballance pipes between pairs of carbs??
Best regrads
Mike
poppet valves rule!

chuggernought
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Post by chuggernought »

yep, take on board all the above, have to say i fitted them with some minor tweaking and a clean out over a year ago with a view to tuning them properly once the rest of the motor was sorted, but never got round to it and havn't touched them since.
the set up runs incredibly well and suprisingly efficent at about 22-25 mpg.
it has good torque throughout the range and a pick up like a kick in the arse.
like yours it has k and n's and does appear to have different rated piston springs, other than 4 into 1 exhaust manifolds the rest of the lump is stock 3.5.
very impressed so far on and off road, certainly far better in power and economy than my disco 3.9 disco (12-14mpg) with efi or 4 barrel eddy(15-20 mpg) on my range rover, not bad seeing as they are all basically the same vehicle and similar weight.
just need to tune properly now and the big challenge, fit lpg to 4 s.u's as far as i know no one else has done this.

kiwicar
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Post by kiwicar »

Is your disco in "limp home mode"?? or do you have a a shall shed attached to the roof? :lol:
I found the boxer set up failey economical, but it was hard to tell as I used it virtually all the time to tow a trailer or throw mud around the place.
Best regards
Mike
poppet valves rule!

chuggernought
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Post by chuggernought »

disco's an auto, nuff said! never got a series v8 disco of any type to do more than 16 mpg at most though, thats what happens when your car is a bit fat and as aerodynamic as a cathedral! dont beleive anyone who spouts off about 30 mpg from a rover v8.
perfect family motor and dog carrier though, missus is happy and it leaves me with me toys, anything less than 8 cylinders is irrelevant.

kiwicar
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Post by kiwicar »

Hi
I had a 3.9 RR on an auto box, normally got 16 to 18 mpg, even got 21 on a run to the lakes (and down to about 12 once there) just I had a period of 12 to 13 on normal driving and upon investigation I found a duff watwer temp snsor and the ECU in limp home mode, when sorted it went back to 16 to 18 and no I don't believe in 25 to 30 MPG figures claimed by some.
Best regards
Mike
poppet valves rule!

olly_richman
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Post by olly_richman »

my 3.9 disco does 17mpg average, have had the magic 24mpg on a 200 mile motorway journey on cruise control!
Morte importantly it will do 19mpg on gas on a motorway run! on the same journey my dads Freelander 2 Diesel cost more to run.

My 1971 rangey on twin SU's however only manages 15mpg average and 18 on a run (petrol)

My disco hit the 12mpg mark when the fuel pressure reg. was broken.

Riley RMF
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Post by Riley RMF »

kiwicar wrote:Hi
I had a set of these a few years ago on my range rover, and I have posted up some of my experiences with them on here before. I was in tough with the chap who designed the system when I installed mine and found the following.
1/ the carb withtwo cylinders firing one after the other (90 degrees apart) on mine needed a the spring in the piston to be slightly stiffer, this I achieved by cutting a couple of coils off and stretching it
2/ same piston required thicker oil in the dashpot (I used hypoid 90 I think)
3/ again on this carb I ran it "leaner" by putting the needle in the piston on the lower indent (to get over the richening effect of the heavy "pulsing" on this carb.
4/ springs in all 4 SUs were lighter than standard, but I don't remember which ones I used
5/ the needles rcommended had a richer top to them, but I think 3/4 of the reason for this was the K&N filter kit I had.
6/I rounded the leading edge of the piston on each carb, this again richens the top end of the rev range.

To be honest I found the whole set up very difficult to keep running in a good state of tune, if I had new carbs and unworn linkages that would have been better (I modified my carbs eventually to eliminate 1 set of linkages which improved things). The set up was very good off road in that it was pretty well imune to being at odd angles, and pickup was good but I felt it would have been better with more development. Maybe bigger ballance pipes between pairs of carbs??
Best regrads
Mike
Question for Mike!

You seem to be the guy with most experience and knowledge on the boxer carb setup, and lots of great advice on how you made them work.

I'm planning to try the Boxer setup with HIF44's, but do you know what needles you were using? Any thoughts as to how needles might change on a 3.9, or my particular interest a 4.3?

Cheers

Phill

Riley RMF
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Post by Riley RMF »

Hi guys,

I've started a new thread on this item here:

http://www.v8forum.co.uk/forum/viewtopic.php?t=14815

So please respond to anything on this there

Thanks

Phill

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