side valve carb needle

Post by **ian.mcdougall** » Thu Aug 21, 2008 7:47 pm

Looking to refurb my carb, just looked at my carb needle and it has GG stamped on it, the only one sold for the sidevalve is an EK The GG would appear to be for an 803cc OHV. Are the needle sizes set in stone, or are they dependant on using the one that gets the car driving most efficiently

Post by **mike.perry** » Fri Aug 22, 2008 12:55 am

The GG needle is the standard needle for the 803 carb, so I would have expected it to be on a semi downdraft H1 not a sidedraft. There must be some science in selecting different needles for different engines otherwise SU wouldn't make over 700 of them. Amongst other things alternative needles cater for atmospheric variations at different heights.
In my MM I use the rich needle M9 as it has the same profile through steps 1 to 7 as the standard EK needle and then continues to taper whereas the EK needle is parallel for the top half of its length
Visit website www.morrisowners.co.uk , click on engines, then on carb problems and read my comments 'cause I can't be bothered to type it all out again.

Post by **alanworland** » Wed Sep 03, 2008 9:48 pm

Does this mean that the EK needle will give a richer mixture than the M9 at tickover revs? - if the taper continues there must be less 'petrol flowing area' available?
If that is the case why would it (M9) be referred to as a rich needle?
I find my tickover is slightly rich, but if I weaken to get a correct tickover mixture the running mixture is weak - to be avoided at all costs!

Post by **mike.perry** » Thu Sep 04, 2008 12:20 am

If you study the needle charts you will see that there is very little difference between needles at stage 1 which is the tickover position, so in theory it would not matter which needle you fitted if the engine was just going to tick over. If you have problems with the mixture at tickover I would suggest that it is either a worn needle or jet or both or the needle incorrectly set in the piston, or the piston is not dropping onto the bridge with an audible clunk when you lift it with your finger.
Stages 2 - 7 are the gentle acceleration and medium speed cruising positions. As I previously stated the EK and M9 needles are identical over this range. The EK needle is then parallel for the top section of its length whereas the M9 needle continues to taper so in theory should give a richer mix and more acceleration under full throttle. I could however be proved wrong. As I've said in one of my threads buy the books and all will be revealed.

Post by **alanworland** » Thu Sep 04, 2008 9:38 pm

New needle/jet, centred, piston nice and free. Not rich enough to hunt but a very 'solid' exhaust note and shows rich colour with colourtune?

Post by **mike.perry** » Thu Sep 04, 2008 9:45 pm

Is the fast tickover screw clear of the cam when you set the tickover which should be approx. 2 turns of the adjusting nut from the fully closed position.

Post by **alanworland** » Thu Sep 04, 2008 10:14 pm

Yes, cam is clear of fast tickover screw.
Initially when I got the engine running after its big layup and with the rebuilt carb, distributor and new plugs I set the mixture with the colourtune, as suggested at tickover to obtain a nice blue colour, it would only go yellow upon blipping the throttle.
However I found that after removing a plug after a good run, that it was erring on the weak side, so, rather than risk burning valves, I have adjusted for a good coloured running mixture.

Post by **mike.perry** » Thu Sep 04, 2008 11:55 pm

Bear in mind that the MM was designed to run on 80 octain pool petrol so it would probably benefit from a different needle using modern 95 octain unleaded and maybe more advance on the timing. However it would need someone to put one on a rolling road for a complete analysis.

Post by **bmcecosse** » Thu Sep 04, 2008 11:59 pm

Colourtune is not necessary on an SU carb engine - just test the mixture with the little 'lift' pin. Many factors can affect the mixture when running - needle profile is one, but piston spring strength and damper oil viscosity are important too. What colour were the plugs after that run alan ? Light beige is correct - pure white would be a bit too weak, and brown/black is of course rich.

Post by **mike.perry** » Fri Sep 05, 2008 12:34 am

Just me being picky but the H1 carb was not fitted with a piston spring and not all H1s have a lift pin.
I'm going to bed
Goodnight.

Post by **ian.mcdougall** » Fri Sep 05, 2008 6:07 pm

what a response from one question my carb does not have a lift pin but it does have a spring if you go to section B fig B15 it shows a spring ????

Post by **alanworland** » Fri Sep 05, 2008 8:56 pm

After a good run the plugs are a nice beige colour so I believe the 'running' mixture to be correct, which can be confirmed with the lift pin, except that I havent got one either! but there is a hole where you can put a drill shank up.
My carb does not have a spring (never has) which is confirmed in the SU Catalogue but the manual is a bit misleading I think. I think I am right in saying that most SU's have a spring?
Surely the damper oil is important only while the piston is rising, the thicker the oil the slower the rise and the richer the mixture is while undergoing acceleration? I tend to use 3 in 1
Good point about the petrol, I was forgetting that I used to run on 2 star!

Post by **mike.perry** » Fri Sep 05, 2008 10:20 pm

SU Reference Catalogue. P 108 & 112:-
Minor MM 4 cyl 918 1948-50. Carb AUC 505 (1), Type H1, Weak Needle MOW, Standard AUD 1158 EK, Rich M9, Spring Nil
Minor MM 4 cyl 918 1951-52. Carb. AUC452 (1), Type H1, Weak Needle MOW, Standard AUD 1158 EK, Rich M9, Spring Nil