Carb too rich

[hdavy]

I had to change the jet to get a new pipe float chamberto carb because all in one unit. Since then I have not been able set the mixture corrrectly which seems too rich. Have screwed the adjusting nut right up. If lifted the piston drops down cleanly with a click. Lifting the piston pin speeds up the idling which indicates too rich. With no choke the jet is very slightly down and lifting it also speeds up the idling. Any suggestions?

[bmcecosse]

Hmm - is it definitely a 0.90 jet (I'm assuming an H2/HS2 carb) - from a reputable supplier? Have you compared it with the old jet? And the 'choke' is definitely not holding it down slightly? Did you move the needle at all- perhaps it needs to be reset slightly lower down in the piston.

[minor65]

Screw the mixture nut completely home / upwards. Then screw it down 10-12 flats. The correct mixture is normally not to far from that. But only do this after a good run when engine at a good temperature. Then set the idle speed accordingly.

[hdavy]

Jet came from Moss. Surely if I screw the adjusting nut down at all it will increase the richness?

[hdavy]

Oh and I didn't move the needle.

[bmcecosse]

Indeed it will.....don't do it. You really need to inspect the jet hole to determine the size.

[mike.perry]

If it is your Series MM then it is an H1 carb. I have the same trouble with my carb, it seems to run permantly rich, even when the jet is wound fully up. Part of the trouble could be that the jet seals need replacing, I have a set but have not got around to fitting them. Fuel consumption is a bit high.

[bmcecosse]

The H1 doesn't have a 'pipe float chamber to carb' so it obviously can't be that - must be an HS2.

[hdavy]

Thanks guys. On my 1098 1971 traveller. I will take jet off again and measure it. Should be 0.9 cm?

[bmcecosse]

That would be HUGE !!!

[hdavy]

OK so 0.9 of what?

[philthehill]

The measurement should be 0.090" (inch)

For all things SU go to the Burlen Fuels Technical pages and there is a comprehensive run through of SU carb details and the setting up procedure.

http://sucarb.co.uk/technical-su-carburetters

Assuming your carb is the usual AUD 13 type here are the details:-

http://sucarb.co.uk/carbspec/carburetto ... s/id/1907/

[bmcecosse]

Sorry - yes 90 thou - but maybe yours has been machined oversize - or they sent you a 100 thou jet. The 'minty lamb' website compares all the needles by jet size.