[mish_mish]

I am finally done balancing carburetors, using German made air flow meter I got on eBay. Both air flows are within 1/100 of the scale, the secret was in finding adjustment on the arm that goes from left carb to the right one.
So the difference is very noticeable, no more pulsation while sitting still in traffic, also better throttle response.
One question though, how do I adjust "volume" screw? Is there some scientific way to do it (like CO2 metering), or do I just turn those in and out, until performance / economy is better?
See some pics...

 

[Dounraey]

The volume screws are for fine adjustment of the air volume when balancing the carbs. You have done it using the coarse adjustment of the adjustment screw on the linkage. Since your carbs are in perfect balance, job done.

The normal procedure is to fully screw in both volume screws and then loosen them by 1 1/2 turns. Set up the linkage and then adjust the volume screws until the carbs are balanced, as denoted by the air flow meter. The volume screws just make the job easier for you. You have done it the hard way.

Geoff

 

[mish_mish]

Great, the story of my life.
So where are the fuel mixture adjustment on my type of carbs?
Thanks

 

[Catullus]

I do not have a picture to send you but I will try to help as best I can. The screws are difficult to see. They are small slot-head black screws with the heads facing upward near the bottom of each carburettor. One could say that they are mounted in a small wishbone. Adjusting these screws makes a huge difference in performance.

 

[mish_mish]

Got it, I know where to look for those.
Right now my plugs look like this (attached), so I think mixture is a bit on a rich side. Also 9 US mpg is probably no the best she can do?

Next few days I will have few hours to put on my white gloves, thanks for your help.

 

[mish_mish]

My plugs

 

[covenant]

I referred to the service manual, and found the following about the coarse adjustment of the linkage(Please see the attached picture).

It seemed like it needs dial gauge in place of the damper on top of the carburetor.

Any alternative way to do this linkage setup? or,just eyeball the position of the 2 throttle plates?

 

[Dounraey]

Hi Covenant

Eyeballing the position of the throttle plates is not accurate enough.

The alternate method to using dial gauges as specified in the manual is to use a unisyn carbalancer. These cost about $30. Remove the U shaped air ducts that attach to the carburetor and hold the carbalancer across the "mouth" of the carb. It measures the airflow going into the carb. Set it on the one carb and then hold it across the other. Set this carb so the airflow is the same, using the volume screw.

Geoff

 

[Dounraey]

Covenant

I notice your car is 1975. Are you sure the attached diagram is the same as on your car. Mine is a 74 car with the earlier linkage where the eccentric throttle adjuster is very difficult, if not impossible, to access. The linkage was redesigned for the series 2 cars. It may be you car, being a late SY1 has this later linkage,

Geoff

 

[guyslp]

One of the best references for "when did that change" on these cars is the Chassis Number Booklet published in 1983 that covers production changes from the first Rolls-Royce up through the end of the Shadow Era.

Since covenant doesn't give his full chassis number it's impossible to know whether the throttle lever modifications apply to his car. They started at chassis number 21324 for coachbuilt cars, 21366 for LWB cars, and 21441 for SWB cars.

 

[covenant]

Thanks for the info.

Will this uni syn carb balancer do the job?(Please see the attached picture from amazon) How about the air flow meter shown at the thread starter's post, which is better or this car's application?

Thanks.

BTW, the eccentric screw shown in the picture is the same as the real thing on my car.

 

[MonsterBabyBLN]

Quick question to this old thread as I have a problem syncing the carbs with the linkage on my 78 hif7... Do these have a volume adjustment screw like the older HD carbs? Is there another way to set them up besides the linkage screw?

 

[Jeff R 1]

It doesn't look like they have a volume adjusting screw.

Tuning - Multi - SU Carburetters

 

[Wraithman]

Balancing the carbs is best and easiest with dial gauges.The workshop manual is your guide, read it and you will come away with how to perform balancing the carbs.

The Rolls

 

[Kelly Opfar]

I have balancing kits in stock:

RR/B Jaguar SU HD8, H4 Carburetor Synchronizing Kit RH8841 | britishtoolworks

This kit allows you to synchronize your SU carburetors by comparing the piston lift in the vacuum chambers with a pair of dial indicators and adjusting the airflow accordingly. The kit includes brass collars with thumbscrews, a pair of dial indicators and indicator extensions.This kit is...

www.britishtoolworks.com

 

[MonsterBabyBLN]

Yes. Vasco here. Bought those. Excited to try them. Just wondered if I have anything else to balance besides the linkage screw.. Like the vacuum screw is on the older version

 

[Wraithman]

The linkage screw is set loose so the carbs can be independently adjusted to the same performance and then physically linked together by the linkage between them.

 

[MonsterBabyBLN]

That's what I read, yes. What I don't understand is that I can hardly make any adjustment as the linkage on the throttle flap has a notch for the screw of the arm. You know what I mean?