XK120 Carburettor Needle

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XK120 Carburettor Needle

Postby Oldclassic » Thu Mar 07, 2019 4:50 pm

Hi All, new to this so any help would be useful.
I have recently purchased an XK120 OTS and notice that it is fitted with W02 needles, (H type Thermo SU's). The information I have found suggests that these are for cars with remote air filters. I have pancake filters and again information suggests the requirement is for RF needles.
What I can't find and hoping someone knows is how much difference is there between the W02 and RF needles. The engine runs well but is definitely running slightly rich.... although this may be more down to my inexperience in tuning :? (just getting to grips with colourtune).
If anyone can suggest that these needles are "wildly different" or "pretty much the same" I would appreciate.

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Re: XK120 Carburettor Needle

Postby mike020150 » Fri May 03, 2019 10:11 am

The differences between carb needles form part of the disappearing art of carb tuning. For the small costs involved, it's worth following perceived wisdom and using the recommended needles for your car's air filter arrangement. The alternative is always a risk that the car will run an incorrect mixture in some part of the rev range and that may carry a small risk of engine damage as well as poor performance. Mike.
2014 XK Dynamic R convertible; 1977 Daimler Double Six Coupe; XE S

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Re: XK120 Carburettor Needle

Postby PPV » Fri May 03, 2019 11:06 am

Have you spoken to the likes of Burlen as I have found them very helpful when trying to sort my carbs? Although I have used Colourtune and found it very useful for initial settings I have found that a CO analyser better at getting it just right but that does not help it right througout the rev range in my experience. I would stick to the standard needles for the car as when tuning SU's then the usual method invloves removing the air filter anyhow to get airflows right and unless the 'new' filter has vast differences to the standard system then it should be ok.
Paul V
Mk2 3.8
Mercedes A45 AMG
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Re: XK120 Carburettor Needle

Postby piman » Sun May 05, 2019 4:51 pm

Hello Old Classics,

Burlen publish a small booklet with needle dimensions.

From that book:-
RF .100, .095,.090,.0863,.0802,.0768,.0732,.070,.0665,.0630,.060.,.057,.054,.051
WO2 .100,.095,.091,..087,.0835,.081,.0785,.076,.0732.071,.0683,.0657,.063,.061
So your WO2 is a weaker needle all the way from station 3 to 14, by quite a bit as the stages go up.

Mk 2 3.8 (long term restoration), MK1 Triumph 2.5 P.I.,2.5 X Type Estate, 564 Hymer Motorhome

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Re: XK120 Carburettor Needle

Postby Oldclassic » Tue May 28, 2019 4:49 pm

Many thanks to all who replied. As suggested I think next time I'm ordering from Burlen (perhaps some of their advertised "super dry" jet assy)
I will also purchase the RF needles and evaluate.
Thanks again to all.

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