Page 1 of 1
Carb too rich
Posted: Wed Dec 30, 2015 5:51 pm
by 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?
Re: Carb too rich
Posted: Wed Dec 30, 2015 6:12 pm
by 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.
Re: Carb too rich
Posted: Wed Dec 30, 2015 6:15 pm
by 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.
Re: Carb too rich
Posted: Wed Dec 30, 2015 6:22 pm
by hdavy
Jet came from Moss. Surely if I screw the adjusting nut down at all it will increase the richness?
Re: Carb too rich
Posted: Wed Dec 30, 2015 6:24 pm
by hdavy
Oh and I didn't move the needle.
Re: Carb too rich
Posted: Wed Dec 30, 2015 7:05 pm
by bmcecosse
Indeed it will.....don't do it. You really need to inspect the jet hole to determine the size.
Re: Carb too rich
Posted: Wed Dec 30, 2015 8:17 pm
by 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.
Re: Carb too rich
Posted: Wed Dec 30, 2015 9:36 pm
by bmcecosse
The H1 doesn't have a 'pipe float chamber to carb' so it obviously can't be that - must be an HS2.
Re: Carb too rich
Posted: Thu Dec 31, 2015 7:54 am
by hdavy
Thanks guys. On my 1098 1971 traveller. I will take jet off again and measure it. Should be 0.9 cm?
Re: Carb too rich
Posted: Thu Dec 31, 2015 10:05 am
by bmcecosse
That would be HUGE !!!
Re: Carb too rich
Posted: Sun Jan 03, 2016 11:27 am
by hdavy
OK so 0.9 of what?
Re: Carb too rich
Posted: Sun Jan 03, 2016 1:51 pm
by 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/
Re: Carb too rich
Posted: Sun Jan 03, 2016 2:35 pm
by 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.