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MG MG Y Type - jet won't go high enough

I have a problem: I can't get the jet high enough to get the correct leaner mixture: it stops +/- 1mm from the seats edge.

On inspecting the carburettor I noticed that the needle was mounted much to low in the piston. Stupidly I disregarded my own rule never to correct a wrong situation if it fI corrected this and tried to adjust the mixture (with the Colortune glass sparkingplug; when the combustion ignites blue, the mixture is right. Very nice to use, but thats another story, perhaps worthy of another thread). I did not succeed because the jet won't go high enough, so I mounted the needle back to it's lower position and turned the jet even lower to adjust.

As I don't really like this situation I'm going to dismantle the carburettor but before doing that I would like some advise on the possible cause of the low jet. I would also appreciate a source for a detailed "exploded view" of the carburettor: I feel the pictures in the service manual don't seem to explain things to me properly.

By the way, three needles are mentioned in the manual, my Y has the leaner one (don't ask the code now). Would I be better off with the normal needle?

Greetings,

Willem, Y5888
Willem van der Veer

I am no expert on this sort of thing, but I think you might be.

Neil will add something I am sure to advise on the situation.

Paul
Paul Barrow

The geat beauty of the SU is its extreme simplicity: there really isn't much to fiddle with.

If the jet is too high or the needle is too low, then I suspect someone has tried to produce a correct mixture setting with either a worn needle (too small) or worn jet (too large) - the effect is the same. The only real solution to this is to replace both, and make sure that the jet and needle are centred properly and that the cork seals at the base of the jet assembly are renewed too. The cost is tiny, and the effect on running remarkable! Good luck.
Tim Griggs

Tim,

Thank you for your comments. The jet isn't to high, its too low and I can't get it up (the jet that is) so I compensated (as the former owner did) with putting the needle to low (I described it wrongly).

So, as you are, I'm a great fan of SU's but on all the SU I worked on before I could turn the jet higher than this one, thats all.

I'll keep you posted if I find the cause.

Willem
Willem van der Veer

Willem - If that is a good e-mail address after your name, I could scan and send an exploded view to you from the Burlen Fuel catalog.

Is the jet low in the upper bearing or is the bearing also low. If the bearing is also low then I would guess that someone put two washers on the bearing for some unexplained reason. That would shift everything down the thickness of the washer.
Good luck - Dave
David DuBois

Some people set the needle and jet low in order, believe, to correct poor tickover ( I think). The idea is to create more turbulence due to the step thus created and thus achieve better mixing. At least I think that is the way it works.
ian thomson

David,

The bearing isn't to low, its about flush with the carburettor body

Yes, thats the correct emailadress and a Burlen-scan would be much appreciated!

Willem
Willem van der Veer

This thread was discussed between 03/11/2003 and 07/11/2003

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