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MG MGB Technical - GZ needle

HI,
i have changed my needles from GZ to #6 as suggested previously, because i have a HS4 with K&N filters, but i noticed its too rich, lots of black smoke.
do i have to retune them?
where does this #6 needles work best on high or low revs?
Alfredo
Alfredo

There is a needle chart avaiable, could any body supply it?
thanks
Alf
alfredo

http://www.teglerizer.com/suneedledb/index.html

or

http://www.rrocncr.org/technical/SUChart/SUChart.html

Greg Smela

Scott Beavis' free WinSU programme is brilliant for needle comparison and spec. Very easy to use, it gives all the specs but, more importantly, allows you to compare 2 needles by relative richness on a graph,

http://www.winsu.co.uk/

or just the download,

http://www.beavispits.co.uk/winsu/winsu152.zip

The SU jets are all the same and may or not be worn. GZ needles are VERY weak, more so than FX even, and far more than the original 5 or richer top end 6.

Compared with GZ the 6 are richer all the way through as you'll see on the graph. This should mean that all you need do is turn up the jet nuts a few flats which should allow clean idling without going lean further up. I'd reset to level then back off 10 flats and go from there.

Rich

According to the charts it looks as if GZ needle is a weak misture, therefore i should use either FX or #5, i think #6 is too rich for a std engine.
thanks
Alfredo
Alfredo

Hi Alfredo, Compare 5 (standard needle) and 6 (rich) and you'll see they only differ by 6 being richer from half to full throttle, they are the same idle to half. 6 is recommended with free-flow air filters such as K&N so I'd have a go at resetting them with the jet nuts.

Rich

Rich,
I will reset the jets as you mentioned, and come back.
alf
alfredo

Alfredo, before you start are you sure that you have set the step on the needles flush with the bottom of the piston. Then start off as Rich suggests and probably weaken from that point.
Iain MacKintosh

for what i understand i have to bring back the jets flush to top, then fit the needles on the piston and sit them in the jets, then undo 10 flats, and work from there as per manual i think.
alf
alfredo

Careful Alfredo. Set the jets flush with the bridge and back each off ten flats. Fit each needle into the piston and adjust until the step on the needle is flush with the end of the piston then tighten the grubscrew. Place the piston assembly into the body with the needles going into the jets.

As you adjust the mixture it is very important that you alter the mixture equally on each jet nut so when you flush them with the bridge it would be benificial to put a reference mark on them.
Iain MacKintosh

I had no 6s fitted for the same reason and went back to 5s. The 6 seemed to rich everwhere although if you use the haystack program they look fine.
S Best

Only today i had a chance of change the needles, it sounds and is responding nicely, i still have to take the car to a spin. Basicly i set them as per your instrutions, i have no gas analizer.
alf
alfredo

I took it for a spin and it does make a diference, #6 to GZ, is like night to day.now i know why could not get a steady speed.
alfredo
alfredo

Excellent, thanks for letting us know. I'm not sure why yours had GZ fitted, very weak, maybe it was a later emmissions spec.

I found a similar improvement when I went back to the original spec 5 needles from the later FX using standard air filters. The car is much more responsive and driveable.

Rich

Rich, i have no idea why was using GZ, i bought this car 5 years ago, and battle to set it right.
now iam going to look at my other 80B with HIF4 carbs, ex USA without those US legistation bits and pieces.
i think the needles are ABC, with K&L filters, but i have a new spair pair of AAAs that came with car.
this car is even slower than the 71B i just done carbs.
thank you for your help
Alfredo
alfredo

This thread was discussed between 14/07/2005 and 22/07/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.