I was wondering if anyone knows if you inverted the HS-6 float bowl and put a manometer in the air chamber damper's dust cap if you could run an SU upside down. I have HS4's on my '67 MGB GT and they are really good, especially in the elevation changes we have around here in the foothills of NORCAL. I haven't noticed the lack of accelerator pumps on these carbs to produce soft acceleration at uptake.
Will an SU (HS-type) work upside down
- Thread starter L.E.N.
- Start date
I cannot imagine the SU's on my old sprite could ever operate upside down for an instant !,
fuel would p*ss out all over the place - but I'm not familiar with the HS4s....
The ins and outs of SUs or CV carbs or vacuum type carbs has been extensively discussed elsewhere.
We are all familiar with the concept that CV type carbs are no better or worse at 'adjusting for altitude'
than manually operated slide type carbs - IF THE THROTTLE ISN'T EVER OPENED TOO WIDE ?
The CV Bings in my old BM had instructions on how to lower the needle and fit smaller jets if you decide to
transit say himalayan passes - 16,000+ ft altitudes - exactly like manually operated carbs they would need less needle and smaller jets.
Unless you don't mind chugging some black smoke...
There was a model of SU carb that was supplied to fit Nortons.
Folks recorded good performance, good fuel economy, and slightly less acceleration.
Not that I tried them, but did take of note of this.
Anyone know what precise model of SU that was. ?
Only one would fit in the space between the frame rails, of course.
Hopethishelps.
fuel would p*ss out all over the place - but I'm not familiar with the HS4s....
The ins and outs of SUs or CV carbs or vacuum type carbs has been extensively discussed elsewhere.
We are all familiar with the concept that CV type carbs are no better or worse at 'adjusting for altitude'
than manually operated slide type carbs - IF THE THROTTLE ISN'T EVER OPENED TOO WIDE ?
The CV Bings in my old BM had instructions on how to lower the needle and fit smaller jets if you decide to
transit say himalayan passes - 16,000+ ft altitudes - exactly like manually operated carbs they would need less needle and smaller jets.
Unless you don't mind chugging some black smoke...
There was a model of SU carb that was supplied to fit Nortons.
Folks recorded good performance, good fuel economy, and slightly less acceleration.
Not that I tried them, but did take of note of this.
Anyone know what precise model of SU that was. ?
Only one would fit in the space between the frame rails, of course.
Hopethishelps.
I was hoping you might respond Rohan, I thought you may know something like this. I was just sorta wondering aloud, no project planned. The HS models have a remote float bowl unlike the later SUs. That p*ssing all over was likely the float or connections. Some old urban legend has it that German engineering had to respond to the SUs precise metering at elevation changes (aircraft?) by inventing fuel injection. I hope you know something about this but really only just curious.
Plus I thought perhaps hobot might take the bait.
Lance
Plus I thought perhaps hobot might take the bait.
Lance
We all know that carburetted Spits initially lost power in a dive, and the enemy with injection could just fly down away from them.
Eventually the good guys got injection too.
SU's have that feature that the choke function changes the overall jetting, so altitude compensation can be achieved,
although making it automatic must be interesting.
That was more that I was thinking that SU's (or any carb really) cannot operate upside down,
jets and needles/jets just flows fuel if it is upside down. Until it is all on the floor, or in the engine....
Carburetted aircraft cannot really fly upside down either, unless the carbs are especially adapted for this.
Chainsaw engines have such carbs (and fuel pickups), they work in any position.
I'd be very doubtful SU's could ever do this, although I've not really tried it !
I have a prewar Amal that operates sideways, and they are renowned for being problematic to setup and keep functioning, and leak free....
I have a little accessory adjustable mainjet for a monobloc amal, lets you adjust the mainjet on the fly, so to speak.
Its surprising that amal didn't offer this as standard, although they may have figured this would cause more damage than usefulness,
knowing how riders liked to tinker....
Eventually the good guys got injection too.
SU's have that feature that the choke function changes the overall jetting, so altitude compensation can be achieved,
although making it automatic must be interesting.
L.E.N. said:
That was more that I was thinking that SU's (or any carb really) cannot operate upside down,
jets and needles/jets just flows fuel if it is upside down. Until it is all on the floor, or in the engine....
Carburetted aircraft cannot really fly upside down either, unless the carbs are especially adapted for this.
Chainsaw engines have such carbs (and fuel pickups), they work in any position.
I'd be very doubtful SU's could ever do this, although I've not really tried it !
I have a prewar Amal that operates sideways, and they are renowned for being problematic to setup and keep functioning, and leak free....
I have a little accessory adjustable mainjet for a monobloc amal, lets you adjust the mainjet on the fly, so to speak.
Its surprising that amal didn't offer this as standard, although they may have figured this would cause more damage than usefulness,
knowing how riders liked to tinker....
