12 replies to this topic

[drakey08]

my su hs2 carburettor is not letting the petrol through and i don't know why has anybody gat any ideas on how to fix it, it looks in good shape and their is no obvios problems

[Big_Adam]

stuck needle valve perhaps.

You sure it's a hs2 by the way, and not a hs4.

Also how do you know it's not letting fuel thro.

[drakey08]

stuck needle valve perhaps.

You sure it's a hs2 by the way, and not a hs4.

Also how do you know it's not letting fuel thro.

yea its a definetley HS2

the petrol is getting into the float chamber but we think its not getting past the needle. Is the piston supposed to move up and down when we press the accelerator when the engine is running. we took the air filter off and squirted petrol into the carburettor and engine runs until we stop squirting.

thanks dan

[Big_Adam]

Ah,

Yes the piston should move freely. Hmmm.....if its not getting out the float bowl then there must be a block in the wee pipe that runs from the bottom of the float bit to the jet assembly. Either take the carb off and blast a load of carb cleaner back tho it or get a rebuild/repair kit.

Try giving everything a good clean 1st. See if that fixes it.

[drakey08]

Ah,

Yes the piston should move freely. Hmmm.....if its not getting out the float bowl then there must be a block in the wee pipe that runs from the bottom of the float bit to the jet assembly. Either take the carb off and blast a load of carb cleaner back tho it or get a rebuild/repair kit.

Try giving everything a good clean 1st. See if that fixes it.

hi, we have taken the carb to bits and cleaned it, put it back together once and refitted it to the engine has made no difference we blew through the wee pipe and air flowed through to the other end both ways and seems to be no blockage. where wee pipe is fitted to the jet assembly, where piston needle goes into, there is some sort of device between the wee pipe and the bottom of jet assembly where the pipe goes in, is the pipe supposed to move or whatever like on a spring. it has a copper piece at the base of the jet assembly.

thanks much appreciated
dan

[Big_Adam]

Right,

The jet assembly DOES move. It's moved via the choke. From what I know of HS4 carbs the pipe just joins to a right angle up to the needle.

[attachment=29578:su_us_mi...xhs2_640.jpg]

Bloody odd. Carbs got fuel and your starting with the choke out right. Not using old fuel are you (just trying to eliminate problems)?

[Retro_10s]

Is there oil in the dashpot?

[Bass Man]

there is some sort of device between the wee pipe and the bottom of jet assembly where the pipe goes in, is the pipe supposed to move or whatever like on a spring. it has a copper piece at the base of the jet assembly.

I think you are describing the Waxstat jet here, post some pics so people can have a look. Is the needle secured to the slide correctly, I have heard of these dropping out and blocking the jet. The jet should move easily inside the adjuster screwed to the bottom of the carb.

How did this problem materialise, was it suddenly or after doing work. Is it possible the mixture setting on the jet is so lean it isn't letting enough through to run the engine, I think the default setting to get the car started after a carb strip is 3 turns out.

[Dan]

I think Bass Man is probably right, it's not that it isn't letting any fuel flow at all just not enough (although I do wish he'd stop calling the piston a slide, it's not an Amal! ). After the carb has been stripped and re-built it will need setting up again, carbs don't simply work when they are put together they need tuning to the engine. The initial position for any SU carb is two turns richer from the jet being flush with the bridge. The cables and return stops all need to be setup properly too. Then the car will need tuning once it's running. Also as above check the needle is fitted to the piston properly. I didn't think the HS2 ever came with a Waxstat, I thought that by the time the Waxstat was invented the Mini was using HS4 carbs but there you go.

The piston moves with manifold depression rather than being controlled directly by the pedal, so you will see it moving with the throttle but not so much if the car is just idling or running with no load. It will move a lot more while actually driving.

[Gr4h4m]

there is some sort of device between the wee pipe and the bottom of jet assembly where the pipe goes in, is the pipe supposed to move or whatever like on a spring. it has a copper piece at the base of the jet assembly.

I think you are describing the Waxstat jet here, post some pics so people can have a look. Is the needle secured to the slide correctly, I have heard of these dropping out and blocking the jet. The jet should move easily inside the adjuster screwed to the bottom of the carb.

How did this problem materialise, was it suddenly or after doing work. Is it possible the mixture setting on the jet is so lean it isn't letting enough through to run the engine, I think the default setting to get the car started after a carb strip is 3 turns out.

I set mine to two full turns but I was rebuilding Twin 1.25's. It ran ok with the wrong needle until I could get it to the rolling road... wouldn't stat at first because I had no oil in the dash pot.

[Bass Man]

'PISTON',!! That's the word I was looking for....!!

[drakey08]

[attachment=29633:JET_ASSEMBLY.JPG]

I think Bass Man is probably right, it's not that it isn't letting any fuel flow at all just not enough (although I do wish he'd stop calling the piston a slide, it's not an Amal! ). After the carb has been stripped and re-built it will need setting up again, carbs don't simply work when they are put together they need tuning to the engine. The initial position for any SU carb is two turns richer from the jet being flush with the bridge. The cables and return stops all need to be setup properly too. Then the car will need tuning once it's running. Also as above check the needle is fitted to the piston properly. I didn't think the HS2 ever came with a Waxstat, I thought that by the time the Waxstat was invented the Mini was using HS4 carbs but there you go.

The piston moves with manifold depression rather than being controlled directly by the pedal, so you will see it moving with the throttle but not so much if the car is just idling or running with no load. It will move a lot more while actually driving.

HI, THANKS FOR ALL YOUR REPLYS, HERE IS A PICTURE OF THE JET ASSEMBLY. I THINK THAT I HAVE JUST REALISED THAT I GOT A HS4 JET ASSMBLY ON A HS2 CARBURETTOR, DO YOU KNOW IF IT WILL IT STILL WORK. ALSO MY NEEDLE HAS A SLIGHT MOVEMENT FROM SIDE TO SIDE IS THIS OK

[Big_Adam]

yep, thats a hs4 WAXSTAT and it shouldn't even fit your car as hs2's use a screw on the choke mech, a hs4 they use a clip.

Yes that bits suppost to move up and down, below it is a copper looking disk. This is a thermostat it changes size on temp conditions so when it's hot the mix is leaned out, cold then its richer.