Twin SU Carby question

[Rata Road]

I have just got a 1928 Triumph Super 7 Sport (832cc) that has twin SU's fitted to it when built up and basically never been running. I have played around with it and it now starts great when warm and drives ok except idling is erratic and gear changing with a crash box is difficult. 

I'm not sure what the carbs are off maybe a Morris 8 from a similar era, they are a 1 inch throat.

Question is how do I work out what needle and jet set is best for this engine? Is there a formula etc?

Thanks

 

[George Cole]

Neat looking car.  Looks like a lot of fun.  Check out Burlen Fuel Systems in the UK.  They either have or make parts for practically all SU carbs.  You should be able to enter your carb number and get the info you need.  If not, contact them directly and they'll help.  

 

https://burlen.co.uk/

 

[Terry Bond]

Your car originally came equipped with Zenith carburetors.  Those SUs currently on it are way too new.  The carbs could be from most anything including an MGB. 

I'd think you could experiment a bit to first find a vacuum leak on the intake side. You could also try to fiddle with mixture settings to lean them out slightly, then balance them carefully.  Lots of You Tube videos to show you how to adjust before you start playing with jets and needle valves.  The SU's might work ok and they are a lot simpler to work with than Zeniths.  But - if you want to be correct, find some Zeniths.  Factory literature is available to keep you right.  There will be a few literature vendors at Hershey with good resources for original info and even some parts.

Terry

[1912Staver]

To start with I would make up a single carb adapter and start with a Morris Minor or similar stock spec S.U.. Like Terry says , those are much newer carbs than your car. My guess would be early Sprite or Midget, circa 1960.  Way too much carb for a small displacement , side valve from the 1920's.

Best tool for setting the mixture on a S.U. , assuming the carb itself is in the " ballpark " regarding size and needle is a Gunson Colortune.

 Morris Minor  or early Austin Mini set up  should get you close. Then it is just a matter of set up.

 

 

Edited September 20, 2022 by 1912Staver (see edit history)

[Rata Road]

Thanks Guys, You could be correct as far as vintage as the Morris 8 SU's were 7/8th and these are 1". I have 2 spare motors which have the factory single carb/manifolds which I could clean up and try if I have no luck with these.

George I'll try putting info into Burlens site, Thanks.

 

 

[oldcarfudd]

From the pictures, I'm guessing he's a long way from Hershey!

[DrData]

First, the plungers are from a newer SU…they have vent holes drilled in them. The SUs in my 1950 TD do not have them. Second, it appears you are actually running on one carb, from your picture. In a dual SU setup, the line from the fuel pump comes into the lid of the rear carb’s float bowl. A line then runs from that fitting to a similar fitting on the lid of the front carb’s float bowl. That is the black hose in the picture. In fact, your carbs do not appear to be a matched set, but, rather, two identical carbs. Sorry I did not have a better photo of the setup handy.

 

SU carbs are actually very reliable and simple to maintain. There are a few excellent rebuilders in the MG community.

[nzcarnerd]

From looking at your photos I guess the car is in Otago somewhere.

 

Surely with two one-inch carbs on an engine that small it is grossly over-carbureted? A one-inch carb is plenty big enough for an American engine of around three litres.

 

Regarding shifting gears remember you have to 'double-clutch' - that is, dip the clutch to get it out of gear, let it out and dip again to get it into the next one. Simple when you get the hang of it. If you try to bang it straight through from one gear to another as you do with a modern, the box won't like it. I have seen many videos of people driving crash box cars and it seems they don't know how to do it. You can do it without double-clutching, but it takes careful timing, and understanding what the engine sounds like when the box is ready to shift.

[Rata Road]

Oldcarfudd - yes I'm half the planet away from Hershey lol.

 

DrData - Sorry I should have posted a pic of the carby set up when in running condition with pipes etc connected which I have below. It is defiantly running on both carbs.

Not sure what the difference between a matched set and 2 identical carbs is but the previous owner had fitted these and hadn't got around to the fine tune stage.

Ive tuned them one at a time as individual units as described by the experts before linking them the best I can with the current jet set up however I have ordered some new parts so maybe it will be better after they have been installed.

The black hose on my set up is an equalizer between the 2.

I agree SU are a simple carb and easy to work on but the needle and jet set up is important. for example I was reading an article that an old 850 cc mini automatic has a different set to the manual version of the same motor so getting this right might take some time.

nzcarnerd - Your close with the location, the pic by the lake is the Canterbury/Otago border.

The car looks good with the twin SU's but your probably correct about them being an overkill. I am happy enough to change it to one carb (of any type that works correctly) in the end but I'll play with these first, its interesting.

I probably didn't explain the double clutching issue clearly, I have had heaps of experience doing this as I have many old cars but the triumph is slow and you dont get much time to get it right between 1st & 2nd . Having the engine revving too high makes it impossible. I need it settle to an idle as soon as I remove the throttle and with set up it doesn't. 

 

Thanks heaps for your input guys

 

[1912Staver]

Two identical vs matched set. I think DrData is refering to the float bowls and possibly the choke linkage , except this is hard to see in your photos. Many / most dual carb set ups will have one float bowl at the front and one at the rear. This gives a lot more room for all the choke links and levers. Your float bowls are both to the front. Unusual for a dual carb installation.

 

 

Edited September 21, 2022 by 1912Staver (see edit history)

[Terry Bond]

Yes - you have two carbs, not a pair.  Here is a photo of the setup on an MGTC.  Wonder if you are forcing too much gas through your fuel line setup?  Are you using an SU pump or a newer electric pump with too much pressure?

Terry

[Rata Road]

1912 - I see what you mean about the bowl locations. As far as choke set up your correct but doesn't matter in this set up as only the front carb has the choke cable connected. A bit harder to start from cold but after that no issue.

Terry - I'm not forcing too much petrol in as its only gravity fed from the petrol tank on the firewall (like a Model A Ford). Its out of shot but located about 3 inches to the right of the pigs tale in the fuel line shown. Thats a tidy set up on your MG.

I have a 53 YB, single SU.

Thanks again

[SC38dls]

The Gene Ponder collection auction starts today you may be interested it as it has a lot of MG parts, engines along with carb setups. https://rmsothebys.com/

 

dave s