What have you done today with your Austin Seven

[Charles P]

I don’t know which to congratulate you on the most Malcolm.
Well, I do actually. The car is definitely number 2

Best wishes

Charles

[Terrytuned]

My semi updraught SU also dripped fuel so I fitted a spacer and made alonger bottom bolt which cured it,as I was allways being told your carb is leaking. Terry.

[Malcolm Parker]

My semi-updraught SU has a spacer and longer fixing bolt that a friend kindly machined for me.  It was made so that when the carb was set up on the bench at its correct angle, the fuel level in the float chamber was exactly the same as the bridge in the carb inlet.   I think that the fuel level in the float chamber should perhaps be a bit lower but before I do anything drastic I will run the engine up to temperature and see what happens when I switch it off.

[Steve Jones]

JG used to say that the fuel level in the float chamber should be such that if you blew gently across the bridge with the dashpot/needle/piston removed, fuel should bubble up through the jet, Malc. I think we both appreciate he knew what he was talking about when it came to SUs. I think you're right, though. Get it up to working temp and see what happens before messing too much.

Steve

PS: Setting the fuel level ad hoc doesn't necessarily work. Remember what happened on the Governor’s Sprint the first time we took the LeaF to the Isle of Man

[Howard Wright]

Hi Malcolm, Steve and Terry

I would agree with Steve, see what happens after the engine is warmed up.  My set up only drips when the engine is stopped and is still cold.  

I think the difference between mine and Malcolm’s set up v Terry’s is that on ours the float chamber is fixed to the carb body so any spacer only sets the float level correctly for the semi down draft layout.  On Terry’s set up I think the float chamber can be adjusted separately from the carb body and his spacer allows a much lower fuel intake to the carb whilst retaining the correct float level at the jet.

Quite why that should help I’m not sure but it seems to work.

Cheers

Howard

[Alan]

Fuel level is not supposed to be all that critical on an SU. However years ago a chap from the company told me to pull the jet down 3/8in with the choke and the fuel should just flood the jet.

[Steve Jones]

Fuel level is not supposed to be all that critical on an SU.

Unless it's too low, Alan and the flow of fuel into the float chamber can't keep up with the amount of fuel the engine is using. Happened to me twice. Once at a Sprint on the IoM and once on a hill in Butts Quarry on a VSCC Derbyshire Trial. Both times a dripping carb had caused me to, incorrectly, lower the float level. Both times, fixed the drip but led to the engine repeatedly cutting out and then coming back as the fuel caught back up - kangaroo petrol style

Steve

[Alan]

Steve surely that’s a pump delivery (or whatever) problem and not jet height as such.

[Steve Jones]

In both cases, dripping the result of sticking needle valves and nothing to do with incorrect float level. Needle valves sorted, fuel/float level (in the Float Chamber) back to where it was and normal service resumed. Jet height not touched.

Steve

[Terrytuned]

I set the fuel level the same as ALan when you operate the choke the fuel should flow over the top of the jet, nobody told me this as I learned from experience. When converting a HS2/HS4 carb to semi updraught I fit a disc to mount the float chamber so you can rotate the disc to get the fuel height correct,I don't lower the fuel height in the float chamber.(see photos)  Terry.