Needle lifter for SU Carb?

[minimaniac]

I've just changed the carb on my van from a Solex to SU. The adapter arrived (from Poland) today and I've fitted it. It starts fine, and runs OK but it's a bit dozey when the pedal is pressed. If I hold the carb piston up then it runs fine.

Is there something called a 'needle lifter' that does this job? I've tried a search and not managed to find any real info on these.

If I'm right with this can someone please point me in the right direction of where to buy one or better still how to make one.

Cheers

Dave

[Martec]

To the left or right of the carb throat (on an HS type SU carb) is a small pin that you can push up and it will lift the piston and so the needle, to test if the engine is running weak or rich. Is this what you are refering to?

There are various types of SU's H (very old) HS (roughly 70's) HD (upmarked and 60's) HIF (later type with float chamber below the carb). The big advantage to SU's is that there is a vast range of jets and needles to get the fueling near, also they are economical and give power all through the rev range rather than top end. Best of all there are adaptors to fit LPG to them.

As with most carbs or throttlebodies to small restricts the top end power, to big and air flow is too slow to draw in the fuel or LPG.

The wear points on an SU are the throttle spindle and bushes (air bypasses the jet and idles weak ans stalls) swing needles wear the jet oversize in 30,000 miles and it runs rich. Some idiot may have used emery paper to clean the piston or cylinder so the air gap is too big and the piston won't lift. Others think that by putting thin oil in the dashpot it accelerates quicker??? use engine oil to slow down the piston lifting so the vacuum is higher and a rich mixture is drawn in to accelerate the car.

Best of luck
Brian

[minimaniac]

Hi Brian,

Thanks for that. The engine is a 2litre Peugeot lump with (now) a modified SU HS4 fitted. Ideally I'd like to fit a bigger carb but as the manifold inlet is only 32mm it would be pretty pointless.

Nevertheless, I've had it on the rolling road and the improvement in torque and BHP on petrol is quite impressive

What I am looking for is a means of holding the carb piston fully open (in the up position) when running on LPG. This improves airflow and prevents wear on the needle and jet. I've tried it with the piston 'wedged' in the up position and it does run a lot better and is more responsive.

So, has anyone come up with an idea for doing this?

Thanks

Dave

[rossko]

Drill and tap a nipple into the top of the SU vacuum chamber. Connect to manifold vac via a small solenoid valve, activated by the gas solenoid supply.

[Martec]

That sounds like a simple and brilliant idea.

Brian