Tuning late model CD175 carbs

[Mister_white_keys]

Greetings to the brains trust.

I've been fighting my 2 door Rangie lately in an attempt to get it running right and not super rich. Unfortunately it's a bit of a mix and match kind of beast with the following mechanical package.

1976 2 door body & chassis
Leyland P76 4.4L V8 with parts of Rover (I think timing chain etc.)
LT95 gearbox/transfer
twin CD175 carbs off a later Range Rover (early 80's I think) with the poppet valves in the butterfly's soldered up.

So the issue I've mainly been facing is that the carbs have been running quite rich. I rebuilt the units with new seals, new jets and new needles a while ago but haven't managed to get the tune quite right. I think my main issue is that I'm unsure of the best starting point for the fixed jet height. I would dearly love a pair of the early units with the adjustable jet but unfortunately my wanted ad hasn't yielded much so will persevere with the later units.

I did discover that part of my richness early on was due to blocked float bowl vents that meant the float bowl was pressurised and therefore pouring as much raw fuel down the manifold as it possibly could, this has definitely now been rectified.

Does anyone have a good starting measurement for the bridge of the carb to the face of the jet? I've read on Lotus Elan, Triumph and Volvo forums anything from .070" through to .110" from the bridge down to the jet and for memory I set them somewhere around the .090" mark but between playing with the Rover and other cars my memory isn't the best. I've also got a vague memory that I'm using B1AQ needles as it was recommended to me in order to give the larger V8 a bit more fuelling down low.

The other experimentation I've been conducting with varying levels of success is to get the timing somewhere near right. I've got an electronic distributor in due to the previous unit failing both electrically and mechanically (wear in every component) but given that the manual lists 4 different timing settings at idle ranging from 8 deg before through to 10 deg after and none of these happen to mention the hodgepodge of a motor combination I have it has been a string of 'change a bit, drive, change a bit more, drive' etc. Anyone running a 4.4L in their Rangie that has a good timing setting at idle? I know the ignition curve will also make lots of difference but with the low rev's of the 4.4 there shouldn't be that extreme a difference in the curve up to 4000rpm.

Any advice, suggestions, more questions would be quite welcome. Hoping to get some good info so once I've got my mini off the hoist and back on the road I can jump straight into getting the big beast as happy and smooth on the road as it should be.

Thanks in advance,
Steve

[justinc]

Start the timing at 8deg BEFORE and work up from there. The possibility that the 4.4 is around 9.25:1 compression ratio will ultimately dictate the end result. If running the richer needles you can advance the timing more.

[Bigbjorn]

Unless you are a fanatic about originality, the cure for carb. problems on Rover V8's is an Edelbrock manifold and a Quadrajet carb.

[PhilipA]

The jets are adjustable from the top with a special tool. There are two types of tool AFAIK . The one I have has a U at the end with the prongs facing down.

I used to use a Colortune with the jet tool to get them correct. The colortune is a transparent spark plug and you can see the mixture in the cylinder ( yellow bad blue good blue with yellow flecks very good).
Each carb feeds the opposite bank.
AFAIK you start with the jet shoulder level with the outer "bridge".
Regards Philip A
You can borrow mine if you pay the postage . PM me if you want to. Oh and I also have a Unisyn which helps to balance the carbs.

[Mister_white_keys]

Thanks for the replies so far.

Adjusting the needle through the dashpot is easy enough, I've made up a tool to adjust them, the problem is that they only provide a small amount of fine tuning adjustment whereas the issue I'm having at the moment is that I'm way off.

The jet being level with the bridge is a good starting point, I might try that and work down from there if it's too lean.

Thanks for the offer PhillipA, I've got 2 colourtune units so I can put one on each bank during the fine tuning. I've also welded a bung into the exhaust so I can add a wideband O2 sensor and gauge but don't want to do that until I get it into the ballpark as at the moment it is so rich it would instantly destroy the sensor.

Bigbjorn, I used to have a Holley on the car as that's what it had when I got the car but I much prefer the twin carbs, plus I don't want to have to buy a quadrajet and a manifold when there theoretically shouldn't be anything wrong with the carbs other than my meddling. If I was to buy new bits to change the fuel system I'd much prefer to build an injection system rather than change to another carb.

[DoubleChevron]

this should fix it ......

FiTech Fuel Injection 30005 Easy Street EFI 600HP Throttle Body System Gold 856291005831 | eBay (https://www.ebay.com.au/itm/FiTech-Fuel-Injection-30005-Easy-Street-EFI-600HP-Throttle-Body-System-Gold/232838100345?epid=5017014703&hash=item36363b7579%3Ag%3A~FUAAOSwX2xaw3Og&_sacat=0&_nkw=throttle+body+injection&_from=R40&rt=nc&_trksid=p2380057.m570.l1313.TR12.TRC2.A0.H0.Xthrot tle+body+injection.TRS0)

[Mister_white_keys]

I've looked into the FiTech system, a mate has one to run on his Valiant.

They look like a great unit but it's hard to justify the price for basically an electronic carburettor. For that sort of money, I'd rather a bit more of management from the injection system. My plan for down the track is to salvage the injection bits and pieces off a discovery and then build a Megasquirt or similar system for it. Open's up the tuning as well as the option of programmable ignition.

In the short term though, I'll keep playing with the Strombergs so I can spend more time on the trails and less in the shed.

Cheers,
Steve

[bee utey]

Each carb feeds the opposite bank.


Not quite. Each carb feeds the two end cylinders on the same side and the two middle cylinders on the opposite side. You could install colour tunes into two adjacent plug holes (e.g. 1 and 3) and they would work fine.

[justinc]

Definitely keep the 175s. Not only are they original, they have way better low end than any holley or Rochester carb, and simpler than EFI.

[Blknight.aus]

start with a vac gauge. disable the fuel to the carbies run them dry and then do a cranking test to see what the carb balance is like.

if thats out fix that first,

then do the initial jetting settings with the throttle locked on the idle setting, till your colourtune shows the right colours.

then set the static advance at idle (8-10 degrees of advance).

and recheck the needle settings.

then you can get into doing all the more complicated things.