SU Carb jet assembly

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Nelly
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SU Carb jet assembly

Post by Nelly »

I was trying to remove the nylon fuel pipe that connects the jet assebmly to the base of the fuel chamber (don't ask1) - the fuel pipe came out with the nut and a metal washer but I think there is meant to be some sort of rubber 'olive' on the end? I think this is still inside the fitting in the base of the fuel chamber. If we can get this out is it possible to reattach all the parts to reconnect the fitting or will we need a new jet assembly?!

Thanks.
Felicity and Sam, Owners of 'Nelly', 1955 Black 4-Door A30
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Nelly
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Re: SU Carb jet assembly

Post by Nelly »

Managed to get the rubber olive out and attach the nylon pipe back on, hopefully no leaks! Now just having trouble undoing the lock nut for centring the jet - lots of plusgas now sprayed on and looking for a better fitting 18mm socket (seems the closest metric size for a difficult to find imperial size nut!) Any tips?
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Nelly
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Re: SU Carb jet assembly

Post by Nelly »

Well a new 18mm socket from Halfords and about half an hour of straining(!!) and the locking nut came free. Surprisingly nothing else seemed to be damaged in the process!

Now to the next problem. The SU we bought was a used one but in good condition. It came from a newer A35 van so had an AN needle in. We bought a GG needle (as specified for the 803cc). However, even after an afternoon of attempting to centre the jet, the needle still sticks. It just doesn't seem to want to centre. I don't think there's enough play in the jet and the needle just won't line up. We tried starting the engine with the best we could get it but the piston just got stuck when the engine was running.

Going back to the AN needle and all is fine. Is it safe to use this needle temporarily - I assume the mixture will be slightly too rich?

What is the next step? New needle in case this one is bent (looks ok to the eye)? New jet bearing? New jet?

Thanks for any suggestions!
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Paulc
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Re: SU Carb jet assembly

Post by Paulc »

Does the engine run ok with the AN needle? If it does I'd stick with the AN. Assuming the piston moves smoothly and the spring is in position the SU is a very forgiving carb. The standard setting for the jet is 12/13 flats down from when it is level with the 'bridge'. You can use SAE20 oil in the damper.
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Re: SU Carb jet assembly

Post by A40FARINAGURU »

Paulc wrote:Does the engine run ok with the AN needle? If it does I'd stick with the AN. Assuming the piston moves smoothly and the spring is in position the SU is a very forgiving carb. The standard setting for the jet is 12/13 flats down from when it is level with the 'bridge'. You can use SAE20 oil in the damper.
an 'AN' is a 1098cc standard needle :thumbs:
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Re: SU Carb jet assembly

Post by Nelly »

A40FARINAGURU wrote:
Paulc wrote:Does the engine run ok with the AN needle? If it does I'd stick with the AN. Assuming the piston moves smoothly and the spring is in position the SU is a very forgiving carb. The standard setting for the jet is 12/13 flats down from when it is level with the 'bridge'. You can use SAE20 oil in the damper.
an 'AN' is a 1098cc standard needle :thumbs:
Indeed, hence why I think it'll be too rich. We haven't tested the carb with the AN needle yet but she idles nicely on the drive with it! (weather too wet last couple of days!). We have a new GG needle on order so that might solve the problem. I know that fuels have changed a lot so might not be the perfect needle but got to start somewhere!
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Re: SU Carb jet assembly

Post by A40FARINAGURU »

a 'M' needle is standard for a 948, i've never had problems with that needle
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Re: SU Carb jet assembly

Post by Paulc »

From another post by Edosan

"Think you need to go at least EB, following advice on here I recently changed from standard AN on my 1098 to Weak EB and what an amazing difference, engine running better right through rev range and its the sweetest tickover I've ever had. Reason is basically modern fuels. Needles relatively cheap and so easy to change so suggest you simply experiment and find which one it runs best with"
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Re: SU Carb jet assembly

Post by A40FARINAGURU »

Paulc wrote:From another post by Edosan

"Think you need to go at least EB, following advice on here I recently changed from standard AN on my 1098 to Weak EB and what an amazing difference, engine running better right through rev range and its the sweetest tickover I've ever had. Reason is basically modern fuels. Needles relatively cheap and so easy to change so suggest you simply experiment and find which one it runs best with"
'EB' i think is 848cc standard
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Nelly
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Re: SU Carb jet assembly

Post by Nelly »

A40FARINAGURU wrote:
Paulc wrote:From another post by Edosan

"Think you need to go at least EB, following advice on here I recently changed from standard AN on my 1098 to Weak EB and what an amazing difference, engine running better right through rev range and its the sweetest tickover I've ever had. Reason is basically modern fuels. Needles relatively cheap and so easy to change so suggest you simply experiment and find which one it runs best with"
'EB' i think is 848cc standard
Yes it is, according to your book that you mentioned in a post a while ago :thumbs:

Very week needle on a 1098 then. We will try to get a new GG needle working when it arrives then might experiment with other, weeker, needles to compare.

Thanks all.
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Re: SU Carb jet assembly

Post by Neil Evans »

Nelly wrote: We will try to get a new GG needle...
I recommend you get a new jet assembly and centre it properly as the jet is almost certainly worn as well... They are a trial and error process that you may get right first time or might take a hundred attempts... :thumbs:
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Re: SU Carb jet assembly

Post by Chairman »

Neil Evans wrote:
Nelly wrote: We will try to get a new GG needle...
I recommend you get a new jet assembly and centre it properly as the jet is almost certainly worn as well... They are a trial and error process that you may get right first time or might take a hundred attempts... :thumbs:
Yup, agree with Neil, each time I have fitted a new needle, I have always replaced the jet. Makes life much easier if both bits are brand new. Just make sure the new needle isn't bent though! :whistle:
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Nelly
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Re: SU Carb jet assembly

Post by Nelly »

Took Nelly out for the first decent length drive with the GG needle (now working). How do these plugs look?
IMG_2969.PNG
IMG_2969.PNG (88.74 KiB) Viewed 173 times
IMG_2968.PNG
IMG_2968.PNG (95.14 KiB) Viewed 173 times
IMG_2967.PNG
IMG_2967.PNG (99.54 KiB) Viewed 173 times
Felicity and Sam, Owners of 'Nelly', 1955 Black 4-Door A30
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Re: SU Carb jet assembly

Post by A40FARINAGURU »

Nelly wrote:Took Nelly out for the first decent length drive with the GG needle (now working). How do these plugs look?
IMG_2969.PNG
IMG_2968.PNG
IMG_2967.PNG
middle one looks normal, the other two look a tad weak
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