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MG MGB Technical - What is the correct Carb needle?

HI
I drive a '71 B and have following action done by the engine: the block has now 1950 pistons, it is 18V head fitted with standard specification, a "mild road" Kent Camshaft 270° installed, 45D distributor with pertronix ignitor system and lucas high performance ignition coil, also are fitted a 4 to 2 exhaust manilfold.
I fitted 2 "HIF6" carbs with pan cake air cleaners. I installed needles "BDR" but for my feeling are this not the best needle. The idle is very rough and the CO adjusting is very hard, and also the top engine performance should be better. Can anybody make a recommendation? I think there are not so much drivers who installed two HIF carb's on a "B", or?
BR
Frank
Frank

I had AAA niddles fitted to my car which I ran with various mods but the airfliters were Pipercross foam. I would suggest you contact either of the two companies to see what needles you need Motor build built my engine for me and I would recommend them.

http://www.moto-build.co.uk/
http://www.burlen.co.uk/

one comment I would make is before you start messing around with the needles please ensure that the engine is set up correctly.
Cecil Kimber

A 4 into 2 exhaust manifold?!?
Steve S.

Take it to a rolling road and have it set up properly - it is impossible to recommend a needle for your application and ayone who says otherwise is bullsh*tting.
Chris at Octarine Services

Frank. I am using the AAA needles on a stock 68 B with the HS-4 carbs. I would suspect that your car will need a somewhat different profile with all of the modifications done to the engine. I would agree with Chris that a rolling road session would be the best place to start, but do not know if you could find one in Germany, especially with an operator having experience with SU carbs. One thing to be aware of is that while the -4 series of carbs came only with the .090" jet, the -6 series can have either a .090" or a .100" jet. Hence, before you can do a great deal of research, you need to know what sized jets are in your carbs and make sure the needles, which go by jet size, are currently correct.

Neither of my SU books lists a BDR needle. There is a BCR listed. You might check again to see what you actually have. Les
Les Bengtson

Frank,
You mentioned you have pancake air filters. Could the surface area be so low that the amount of air coming into the engine is less than required?

Ray
Ray Ammeter

Hi
Many thanks for your quick response. Your are right, the best way is to adjust the engine by visiting a rollertest. If I have Holiday I will do this.
The reason for my question is,that recommendation for the competition "stage 3 engine" is the "BDR" needle on "HS6" carbs. I use the "HIF6" carbs with standard cylinder head, but a 1950ccm engine block and the 270° camshaft. Therefore my question to you, used anybody a comparable specification and can tell with needle he drives. For my meaning is the "AAA" very often used for "HS4" carbs?

Thank you
Frank
Frank

Frank. Yes, the AAA needles are often used with the -4 series of carbs, both the HS and HIF models. There is no significant tuning differences between the HS and HIF models, at least at set up. So, if the "BDR" needle is recommended for the HS-6 carbs, it should work on the HIF-6 carbs also. Once again, none of my books lists an needle as a "BDR", although both list a "BCR". Hence, you may wish to check your reference to see if there has been a typographic error or whether this is a recent needle not listed in my books. (The newest book is the current edition with a 1994 copyright date.)

Beyond that, it is simply a case of noting what you have and what you need, then going through the needle charts to find the closest needle to your requirements. If you need a leaner needle, you look for one that is thicker in the areas you need to have a leaner mixture. If you need a richer mixture, you look for a thinner needle. You also need to determine what jet you have in the carbs so that you are buying needles for that jet size. Les
Les Bengtson

It appears the BDR is a .100" needle.
http://www.aptfast.com/APT_Parts/SU_Parts/a_SU_components.htm
Scroll down to .100" spring needles.
The following web site has this information about BDR needles. BDR is only very slightly richer in the low to mid-range and then becomes insanely rich at the top end. There are only about 2 or three needles richer than BDR at the top.
http://www.ime.org.uk/ime/n/needles.html
No solution to your problem, but a reference to BDR needles. Good luck, Clifton
Clifton Gordon

Hi,
Thank you for your good and quick hints

@Cecil:
I have checked until now following thinks:
a. the engine is complete overholed with new pistons, camshaft, crankshaft, cylinderhead.
b. the valve timing is O.K.
c. the compression is at all cyl. 13 bar!!
d. the intake system has no leaks ( checked the compressed air into the carb and leak serach spray)
e. the adjusting of the carb is hard is following poor values: (exhaust) 1000 Hc, 5%02, and 12 Co.
f. without Air cleaner the same complaint.
g. I adjusted the ignition to different values (until engine is pinking and return until engine has poor performance) Now is adjusted to 10° @ 1300RPM's with disconnected Vac.
h. The valve clarance is also O.K. (0,40mm)

@ Steve
sorry 3-2-1 (Falcon big bore exhaust)

@ Chris:
Your are right, it's the best way. (now is winter and the "B" drive only at summertime)"Sundayracer"

@ Les:
the Jet's are LH LZX 1028 Black and RH LZX 1029 White I think it's the correct one. The BDR Needle is recommended by B&G.

@ Ray:
without cleaner the same.

@ Les:
I think the different between and HS6 and HIF 6 is big (different size of throttle and so on).

@ Clifton:
Thank you for WP's it's good.

Has nobody a MGB with same specification and his Car runs well? (1950ccm, standard 18V Head, 270° camshaft and HIF6 Carb's)
Frank

This thread was discussed between 11/01/2004 and 12/01/2004

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