The V8 Owners Forum -

Ive got the above stated engine in my sierra and its running like a bag of bolts, i have no experience with SU's but i am right in saying this is the problem?

Had the plugs out and 4 are lean and 4 are rich. The car has its days when it runs fine and others when all it does is coughs and splutters and pops and bangs.

I wouldnt know where to start with SU's on how to set them up etc but ive had the floats out and made sure the moved freely and also put fresh oil in the dash pots so I now need to set them up to try and fix the running issues. can anyone point me in the direction of anyone around the Fife area be able to set them up for me? Or is there anyone on here that could do and I will pay them accordingly for their troubles.

Thanks in advance!

Also forgot to add that the car is guttless and lacks power big time, i drove a 101 the other day and it went so much better and was a hell of a lot quicker than my sierra.

This is when i realized i had to get this sorted out

May help if people knew where you were located

Andrew

I wouldnt know where to start with SU's on how to set them up etc but ive had the floats out and made sure the moved freely and also put fresh oil in the dash pots so I now need to set them up to try and fix the running issues. can anyone point me in the direction of anyone around the Fife area be able to set them up for me? Or is there anyone on here that could do and I will pay them accordingly for their troubles.

Fife in Scotland just outside Edinburgh

Hi
the SU carb is simplicity itself to get working, you can do this all yourself, honest they are a doddle to get going.
There are three areas to get sorted, the carb itself, the lincages that syncronise the two carbs and the inlet manifold and associated plumbing.
Right lets start with the carbs, you need to check they are working correctly, the areas that cause the problems are, firstly collapsed/ puntured floats, next sticking leaking float valves, both easy to check, is the float in one piece? does it leak? if not replace with a new one. Float valve, check by blowing through it, does it seal if you suck and let air through if you blow? if not take the valve out and check it, if it is badly worn replace it they are just hassel if they stick/leak.
Right main body of the carb, does it have poppet valves on the throttle plates? if yes solder/ glue them closed and clip off the spring bits and throw them away, even better replace the butterflies with plain ones with out the poppet valves. as for the rest of the carb, the best thing to do buy a rebuild kit and replace the main jet and needle and strip and rebuild the carb,. . . . . . .
This post will take all night to write. . . buy an su carb manual and follow that, http://www.haynes.co.uk/webapp/wcs/stor ... &langId=-1
it will cover refurbishment and initial set up, then it is checking linkages and seeing that those work correctly and open both the carbs the same, a piece of 1/4" plastic tube and an ear and you can ballance them very accuratly. Finally check all the manifold and plumbing for leaks and fixing them as you go, 1 tin of WD 40 and a little time and you can sort that one.
It will be quicker to do it yourself than find an "expert" much cheeper, plus with the manual and spending the time to do it youself you will be your own expert, they really are good carbs, and easy to work on, very good to work on.
If you get stuck post up questions, I am very happy to answer anything but putting it all up in one go is a bit much for one evening, lets split it up into managable chunks.
Best regards
Mike

Hi Again
I'll be up in Glasgow over Christmas, if you are still stuck I could meet you for an hour or so and a chat in Christmas eve morning.
Best regards
Mike

Thanks Mike! I might just do that in regards to the manual as the car will be off the rd for the winter. And no doubt i will have some questions that i need answered.

Cheers again mate!

kiwicar wrote:Hi Again
I'll be up in Glasgow over Christmas, if you are still stuck I could meet you for an hour or so and a chat in Christmas eve morning.
Best regards
Mike

If the weather is pretty good i'd be up for that Mike that would be a great help!

I wouldnt know where to start with SU's on how to set them up etc

Hello Hyndy, I just copied and pasted this from my web page.

http://www.vintagemodelairplane.com/pag ... tUp01.html

Setting up and Tuning SU Carburettors

Tools

• Screwdriver

• Spanner (adjustable)

• Spark plug spanner

• Jet adjusting spanner (early cars)

• Carburettor damper oil

• Length of tube or hose

• Carb Balancer - optional

The SU Carburettor is a simple design proven to be very effective. Often underrated, it offers versatility and reliability due to being analogue and the vast array of needle profiles available. In the right hands they can perform better than early versions of computer controlled systems.

Inside the carburettor is a piston which reacts to the rate of air flow to the engine. Attached to the piston is a tapered needle which alters the amount of fuel delivered as it rises and falls. This combination provides variable amounts of fuel and air to meet engine demand under changing loads. They are simple to adjust, but resist the temptation to fiddle unnecessarily.

Only adjust carburettors when satisfied that the ignition system is working correctly

Check Adjustment by inspecting spark plug electrode and exhaust tailpipe colour, an easy guide to how well the carburettors are adjusted. After an extended run to thoroughly warm the engine, remove each plug in turn and compare the colour of its electrodes.

• Brown/grey colour, engine in tune.

• Black sooty deposits, over-rich fuel/air mixture. Also visible at exhaust tailpipe.

• Very light or damaged, abnormal combustion, lean fuel/air mixture

Carburettor Adjustment is made after running up to operating temperature, disconnecting the linkages and removing air filters. Twin SU's are straightforward to set up, with three main areas of adjustment.

• synchronising the carburettors

• setting the idle speed

• adjusting the mixture

Synchronise by adjusting the idling screws on each carburettor to as low idle speed as possible but fast enough for the engine to run reasonably smoothly. Use a length of rubber tube to listen to the intake 'hiss' from each carburettor and compare the sound. Be consistent about the pipe position. Adjust the idling screws for the same sound at each carburettor. Perfect idle match may not hit the part throttle sweet-spot requiring further subtle adjustment, perhaps using a Carb Balancer.

Set Idle Speed by turning both throttle screws the same amount. Once the desired idle speed is achieved re-check the synchronising.

Adjust the Mixture if spark plug colour reveals a mixture problem. On most models, the jet adjusting nut is clearly visible beneath the body of the carburettor. Tighten the nut up to weaken the mixture and loosen to enrich it. An SU jet adjusting spanner makes the job easier. If the mixture is very badly adjusted tighten the nut up fully then loosen it 12 flats of the nut to set it approximately correct. Then continue!

On an HIF carburettor mixture adjustment is by a cross head screw situated in a recess in the base of the body, On later cars, jet adjustment is controlled by turning a screw on the side of the body. Turning screws clockwise enriches the mixture, anti-clockwise weakens it.

Carburettor Lifting Pins at the side of each carburettor enable checking piston movement. Once synchronised, these pins can be used to check the mixture adjustment. Raise the pin on one carburettor approximately 1/32 in (0.8mm).

• If engine speed increases, mixture too rich. If it immediately falls, mixture too weak.

• If engine speed momentarily rises, then returns to idle, then mixture is correct.

Repeat for second carburettor then re-check both since they are interdependent. Refit linkages and filters. If the exhaust note is irregular with a slight misfire and colourless exhaust, the mixture is too weak. If there is a regular misfire in the exhaust note and a blackish exhaust, the mixture is too rich.

Damper Oil is added by unscrewing the damper caps, withdraw the dampers, top up each reservoir with specified oil to 1/2 in (12mm) above the top of the hollow piston rod. Refit.

Float Chambers contains a float and a needle valve that work like a toilet ball valve. As the level of fuel falls, the needle valve opens to allow in more fuel. If a float sticks or is punctured, fuel continues to enter the chamber to eventually exit the overflow pipe. A needle valve can become blocked or stuck and either, not permit fuel to enter, or fail to shut off. Early versions had side mounted float chambers whereas later versions were integral.

Throttle Discs in some units are fitted with overrun depression limiting valves to clean up exhaust emissions by drawing in more air on overrun. If springs become weak and the valves fail to close properly an erratic tick over with a rising idle speed will result. This is remedied by replacing the valves, solder the valves closed or reverting to earlier discs without overrun depression valves.

Cheers Ramon

What makes you think its the carbs? It could easily be a dodgy ignition system or the timing being out.

Jeff

jefferybond wrote:What makes you think its the carbs? It could easily be a dodgy ignition system or the timing being out.

Jeff

Indeed. It's like the injection engines - many blame that for poor running before checking the other obvious things.

First check the compressions are good. And that the cam isn't worn - this is very common on old RV8s. Now check all the plug leads Including king lead with a DVM - burnt out ones are again common. Make sure the carbon brush in the dizzy cap is present and moves freely. Examine the cap and rotor arm carefully for signs of tracking. Make sure the plug leads are laid out correctly. Check the advance mechanism in the dizzy is operating. Then check the ignition timing using a timing light. Many retard the ignition for 95 octane petrol, but this isn't necessary with an engine in good condition/tune.

Once you're sure everything is correct move on to the carbs.

SU type carbs are unique in that if they are out at any part of the engine curve, they'll be out everywhere. Unless the needles have been altered. So a check at idle is a good start - and they provide a method for this. With the engine at normal temperature, lift each piston in turn about a couple of mm, which will weaken the mixture slightly. Some carbs have pins to do this - otherwise remove the inlet trunking. If the engine speeds up, the mixture is too rich. If it slows down or stalls, too weak.

However, this test doesn't show the carbs are perfect - they could be flooding or the starting mixture control playing up. So you must be certain the carbs are working properly before setting the mixture.

If the lean 4 cylinders are 1,4,6,7 or 2,3,5,8 then you do have a carb problem, because they are the groups that each carb does. You can then work out which carb it is by looking at the inlet manifold design.

It's a start!

Chris.

1,4,6,7 = N/S carb, the rest are the other one.