TC carb balancing

Hi,
i am in the process of making a carb balancer where I should be able to see the differences in inlet pressure between the two carburetors by means of 2 jars half filled with a liquid and some interconnecting pipework. My question is , if I had to remove the two crankcase breather pipes temporarily and connect my balancer to these , should the set up work? If both carburetors had a vacuum pipe fitting , I would have used these. Thanks

Richard
 
I do not think, that will work. A vacuum tester should be connected between carbs and manifold, so you must create a socket for connecting the device. Then you need very precise instruments, as the vacuum decreases as soon as you open the throttle. Instruments like these :
Boehm synchronizer for carbs
The crankcase connection should suck out from the crankcase in a more or less constant way, so I do not think, this connection is of any use here. The simpler method is using the intake opening of the carb, there are some threads here, but on this side I would simply buy the Gunson carbalancer.
 
The carb balancer must read from the face of the carb, before the piston. You don't need any jars, look up tube manometer on the net and you'll see how to make a very sensitive gauge.

Yours
Vern
 
If you want any more details on the manometer I made just ask. It just plugs into the face of each carb in turn once the air filter element and cover are removed, just hold the adapter in place to take a reading.
 
Hi all. Thanks for your replies. My idea was to have something that connects to both carbs to compare vacuum levels at a glance. I very much like the link Vern sent using tubing. My only concern is whether there is the possibility of sucking in the fluid, if for instance one of the carb bungs falls off? To date I have always used a short tube placed in front of the piston and compared hissing sound and have been quite happy with the result. I am trying to improve the way of setting them correctly.
I imagined connecting to the outlets for crankcase breathing which are practically in the same place as the outlet for automatic advance would be fine since they are immediately after the piston .

Thanks again.

Richard
 
Generally, the length of the tubing in the manometer will prevent the fluid from being sucked out. In any event, it's only coloured water and so what if it gets sucked into the engine. Water injection is a real thing, and in fact I've added it to several 10:1 TCs over the years to compensate for not being able to get 100 octane gas (water injection helps prevent detonation from low octane gas)

Yours
Vern
 
The port for the crank case breather might not work. Its before the throttle butterfly, but after the piston and the engine draws some of its combustion air from there. If you block it off with a manometer so it can't draw air, it will have to get the extra air past the piston, which will rise, so you won't actually be measuring the idle condition. U-tube manometers with both ends of the U connected work really well on motorbike engines that have vacuum ports for each runner. You measure the relative vacuum behind each butterfly. Because on our engines, we can only measure before the butterfly we need some way of measuring air flow into each carburettor. That's why, when I built the device in the link Vern posted, I created a little venturi. Holding the venturi onto the carb inlet doesn't restrict the engine, but the manometer is sensitive enough to measure the subtle differences in flow through the venturi.

I have an idea it could also be used to set the mixture to find the fastest lean idle too, all be it without the air filter in place. Start slightly lean and as the mixture is richened the flow shown by the manometer should increase as the idle speed increases. When the point is reached where further richening doesn't increase flow, then that should be the right setting. That's my theory anyway.
 
^^^^ I'm not sure that type will fit between the carb and the inner wing on a TC.

I may be wrong though.
 
All this started because i was feeling a slight unevenness in the way the car drove at low speeds, like a vibration in the forward backward plane of the car. If the clutch is depressed , the car smoothens out eliminating anything wrong in the drive train. On high throttle openings the power delivery was smooth and constant. On Saturday I removed the air cleaner and placed a length of tubing before each piston and listened and found that there was a hiss on the front carb and practically nothing on the rear. While doing all this I was smelling petrol and noted that on the rear carburettor the tube between float chamber and the jet was leaking enough to have a constant drip. I removed the carbs ( I could not find a way to remove the jet assembly with the carburetors in place) and found that the seal failed. I will be ordering new seals and jet assemblies today. So this has now changed from a simple setting to an overhaul!!
 
All this started because i was feeling a slight unevenness in the way the car drove at low speeds, like a vibration in the forward backward plane of the car. If the clutch is depressed , the car smoothens out eliminating anything wrong in the drive train. On high throttle openings the power delivery was smooth and constant. On Saturday I removed the air cleaner and placed a length of tubing before each piston and listened and found that there was a hiss on the front carb and practically nothing on the rear. While doing all this I was smelling petrol and noted that on the rear carburettor the tube between float chamber and the jet was leaking enough to have a constant drip. I removed the carbs ( I could not find a way to remove the jet assembly with the carburetors in place) and found that the seal failed. I will be ordering new seals and jet assemblies today. So this has now changed from a simple setting to an overhaul!!
Sorry to hear your carbs were leaking, but the good news is that you'll be back on the road safely very soon now. Burlen's sell complete rebuild kits and parts for SUs that will tolerate modern fuels now. I'd change the jet and hose on both carbs to be safe.
 
Both the jet hose and the little seal on HS carbs have always been ethanol proof, so no real worries there. The same can't be said for the HD jets, the diaphragm on those does deteriorate in ethanol so Burlen changed those to a better rubber.

Yours
Vern
 
Sorry to hear your carbs were leaking, but the good news is that you'll be back on the road safely very soon now. Burlen's sell complete rebuild kits and parts for SUs that will tolerate modern fuels now. I'd change the jet and hose on both carbs to be safe.
I've ordered the parts from MGBD and hope to get them soon. My niece is getting married on the 28th of the month and I promised to drive her there in the Rover. So fingers crossed I get the parts on time.

Regards
Richard
 
Both the jet hose and the little seal on HS carbs have always been ethanol proof, so no real worries there. The same can't be said for the HD jets, the diaphragm on those does deteriorate in ethanol so Burlen changed those to a better rubber.

Yours
Vern
Unfortunately Burlen were out of stock for jet assemblies.

regards
Richard
 
So I have overhauled the carburetors, balanced them and adjusted the mixture. I am fairly happy with the result but will fine tune after a run. At the moment I am still on the rich side with the mixture.
Now question time! The carburettors are HS8s and the engine is a 9:1 CR version.
  • Are the jet assemblies the same for 10:1 and 9:1 CR engines?
  • The 2 pistons do not travel down at the same speed. I tried the pistons on their own, with springs only and with springs and damper. The inside of the domes and the pistons do not have any scraping marks and are practically undamaged. Should this be a problem? They both stop with a thunk!
  • The 2 piston springs are not the same length. One seems stretched. These carbs were never overhauled, and the springs never changed and nobody except my father has ever worked on the car. I could not see any colours on the springs to confirm if they are black/blue. Thoughts?
  • I balanced the carbs by means of a stethoscope with fittings in each throat so one can hear the hiss from each side at the same time. When the accelerator is pressed slowly the rear carb opens before the front one. I think that this is due to the clearance required in the front carb at the lost motion connection. Right?
  • The car idles at around 800rpm . If the engine is raised to above 1500 rpm , kept there for some time - 10 seconds or more- and then the pedal is released, the idling speed will initially start at 1000 rpm for a couple of seconds and then go down to 800 rpm and remain steady but will occasionally falter to 650 and the back up to 800 rpm. Is this the lumpy running mentioned in other posts?
I have taken the car for a ride and performance wise it is healthy but will fine tune when I find the time.

Regards
Richard
 
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