Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing tuning SU HS6 carbs in a '67 +4?

That does sound like the distributor or the fuel supply. Is the pump OK?

I'll check the fuel supply. It starts fine every time. My mechanic recommended re-bushing the distributor, which I figure I will do this fall. I have ordered the colortune.

Check the dashpots side by side to make sure that the needles are at least visibly the same length and profile. Check the dashpot springs. Set the jets at the start visually so that they begin in the same place. I used a tyre tread depth gauge to get them spot on. A turn and a half down to start will be good enough. Set the mechanical linkage with the engine off so that the throttles open at the same time. (Some advocate a slight lead on one carb, but I've never used this method). Also adjust the choke linkage so the chokes activate together. So with the baseline set, you can start up, and warm up. Then first test the open throttle balance at say 2000 rpm, adjust if necessary and then adjust the idle balance. If you want to do the lift pin method, only lift it a quarter inch, not all the way. Adjust the jets the same amount each time to keep the relative position the same. That should sort the balance and mixture.
One colourtune will struggle with twin carbs if they have a balance pipe or manifold link, you really need two. But I've never managed to get the mixture right with colourtune, preferring the old fashioned way!

PS the spluttering at 4500 sounds like fuel supply, check the punp and filter if it has one.

Ok, perhaps I found the culprit of the sputtering. I now notice that the jet hoses are very wet with gasoline, so I believe there is a bad seal somewhere. Both of them are very wet with gas. Could this be the issue with the sputtering? And is this a simple change of the jets, or should the whole carb be replaced?

You should be able to get a refurb kit - Burlen in the UK for example.
http://sucarb.co.uk/?SID=c8fijq3g6c4dlo136f5a0eteq0

If the float chambers are leaking, and the levels vary it will mess up the mixture, and possibly the fuel may be aerated. So fix that first. You may also find sludge in the float chambers.
New needles and jets will make a difference.

You might consider replacing the carbs, but refurbing is very satisfying!

New main jets come with the hoses and seals. If the carbs are old, the original jets are not ethanol compatible and will begin to leak.

Thanks... that is what I figured would be needed. I'll order the parts for the new jets first. If needed, I'll refurb the thing (have the shop do it) if this doesn't help. Joe Curta has a good shop going in NYC: http://joecurto.com/

Here is a drawing (of sorts) that purports to show how the jet hose is held captive by the compressed seal between the nut and the float chamber.

You probably have this already but just in case.
http://mgaguru.com/mgtech/books/pdf/Tuning_SU_Carburetors.pdf

Great link!