Twin SU's

Post by **alanworland** » Thu Sep 04, 2008 9:49 pm

Not very visible I must admit, but there is a 20mm spacer fitted under each carb.
I have a vacuum gauge fitted in the car and wanted to still have it connected but without joining the intakes up, so I have decided to drill and tap these spacers for fitting of a small bore connecting tube with a T piece in it for supplying the gauge in the hope that this still wont let one carb know the other is there

Post by **alanworland** » Thu Sep 04, 2008 10:02 pm

Mike, in your opinion would you think that the setup I am working on would, from a needle/mixture viewpoint be the same, as the engine is at any given time still pulling through an H1 carb?
If as, I think that although the setup might (hopefully!) breath better, it will still require the same 'mix' of fuel and therefore the same needle?

Post by **mike.perry** » Fri Sep 05, 2008 12:07 am

I've no experience of running twin carbs on a side valve so it would be a case of suck it and see. I guess the GG needle would be a good place to start as it was used in the Frogeye and I believe in the Derrington head. I have twins on the Traveller which has a standard MG 1275 setup. They were a pig to balance but I managed to get near enough with a Colourtune.

Post by **alanworland** » Fri Sep 05, 2008 9:07 pm

Thanks Mike, when I get them fitted 'for proper' I shall let you know how they go (or not!)

Post by **RobThomas** » Sat Sep 06, 2008 7:42 am

....and then go into a production run of half-a-dozen manifolds?

Post by **alanworland** » Sat Sep 06, 2008 9:53 pm

I didn't take a note of how any hours went into them, but it is an awful lot! But what better to do on a rainy day(s)!

Post by **tortron** » Mon Mar 09, 2009 5:14 am

what i have so far (have another couple of carbs out in the shed somewhere)

definately off another bmc engine (herald perhaps?)
has stanpart printed on them

Like that they are the perfect distance apart for the sidevalve (extendable along the balance pipe)

obviously some work will be needed to fit the shown side flange to the engine - some sort of adaptor plate im thinking at the moment
However i find it weird that there are no holes drilled in it already?

next step after that is to figure out the linkages and what sort of airfilter set up i want -
-make up an adaptor to run a single standard filter
- run two standard filters
-something shiny (currently bidding on a 10 inch eldelbrook pancake type filter - will probably look naff tho)

Post by **mike.perry** » Mon Mar 09, 2009 3:02 pm

Looking back at those twin carb photos there doesn't seem to be much room to get an air filter on the back one. I think Graham has used an Alexander pancake filter on his single carb Alta engine.
I believe the filter has a flat side which may give it enough clearance.
The other setup is the Monaro 2 into 1. There is a photo posted on page 2 of the cylinder head topic.

Post by **alanworland** » Mon Mar 09, 2009 5:02 pm

I think some manifolds are designed to be just clamped with butterfly type load spreaders, I have some of these taken from an early Viva where the manifold was clamped to the engine in this manner.

Post by **plastic_orange** » Mon Mar 09, 2009 7:40 pm

These carbs look as though they came from a Triumph Herald (sport?/S if my memory is correct). I only know, as I took a set off a Herald in the scrapyard in 1972 (for my A40 Devon). I actually managed to get them fitted and working (had to move them apart a bit - balance pipe separated just enough), but they didn't provide the performance boost I thought. I gave them to my mate for his Standard 10 - improved his performance a bit.

Pete

Post by **tortron** » Mon Apr 06, 2009 9:27 am

but really

have just picked up few carb bits and pieces so now have the dual choke linkage sorted - as well as the butterfly linkage and brass fuel fittings with braided hose

however on closer inspection due to the sloping nature of the standard exhaust manifold this manifold would only just clear (using the h1 carb with the "long inlet end"") however with a spacer/adaptor plate made up it should clear alright - even better to get a heat shield in there

but really all that is just semantics as i will be having a go at building a 4 - 2 -1 exhaust system

Post by **tortron** » Mon Apr 06, 2009 9:33 am

also - i notice the intake ports are square. should i try modify the manifold to taper to a square?

Post by **alanworland** » Tue Apr 07, 2009 11:37 pm

I must admit when I made my inlet manifolds they match the carbs at one end (round) and the engine end is square (with large radius corners) to match the inlet port, and being angled up do give a bit more clearance around the exhaust manifold which I can see would be tight for clearance.
Good luck with the 4-2-1 !
Have you a pipe bender or a 'very helpfull' pipe bending outlet?

Post by **tortron** » Wed Apr 08, 2009 1:29 am

a combination of "scrap bin bends" from the local coby place and motorbike headers

Post by **tortron** » Wed Apr 08, 2009 5:57 am

well looks like i may scrap the manifold idea and make some
thres just not enough clearance (perhaps just enough with the standard exhaust) unless of course i make up some "remote" fuel bowls.

edit:
Thinking about it - the standard intake would work. Maybe that with a bigger carb along with extractors
I am one for having lots of options

Post by **alanworland** » Mon May 04, 2009 6:47 pm

Well, I now have the twin H1's on home made manifolds up and running!
Before removing the original carb and manifold setup I carried a 'time trial' this involved a local dual carraigeway upon which I timed the progress from 40mph to 60mph, in top gear - it took 20 seconds.
After fitting the mod this was repeated, and a reduction in time of between 3 and 4 seconds was experienced!
This was carried out 2/3 times to verify my findings.
EK needles are fitted and the mixture(s) have been setup after several good fast runs (for a sidevalve!) this has ensured the cruising mixture is about right, but at tickover the engine is running slightly rich. Looking at the needle diameter comparison with the GG needle I believe a change to this needle should go someway to correcting this.
The above was carried out using a standard exhaust manifold and 1.25in stainless steel system.
An adapter was made and fitted between the manifold flange and the exhaust system flange into this was fitted an adapter to connect a pressure gauge (in the cabin) during the tests at no time did the pressure go any higher than about 1.5 psi
This I believe shows to me that the existing exhaust adequate and is not restricting the gasflow excessively, although a better manifold would undoubtedly improve gasflow up to the exhaust system.
I hope the above is of interest to fellow sidevalve owners!

http://i248.photobucket.com/albums/gg17 ... winH1s.jpg

Post by **mike.perry** » Mon May 04, 2009 7:22 pm

It looks great. Any chance of some more photos so that we can see from different angles and clearances?
The carbs look like Series II carbs with square bodies, I will check later.
One thought, is there room to swap the carbs over so that the float chambers are on the outsides? It would move them away from the heat especially the front one which would be in the draught from the radiator

Post by **alanworland** » Mon May 04, 2009 8:25 pm

I will take some more photos, preferably in the daylight!
Carbs came from an early Sprite, so the float chambers have a 20 deg angle fitment - so the carb bodies are inclined at 20 deg to suite.
Float chambers could be swapped putting them on the outside of the bodies but I think the rear one would be very close to exhaust manifold!
If probs are experienced later I would fit a heat shield and also consider fitting a fan drawing air from between the engine and chassis rail ducted to blow directly on the float bowls.
I have made things more difficult by fitting float chambers as I have, but it does make a very neat and compact assembly!
I know its not been that hot but I have done some 'creeping driving' (last weekend) which didn't show any probs, other than thinning the 3 in 1 oil I had in the dashpots to the consistency of water making for a very weak mix on pulling away!
20/50 engine oil has however cured this!

Post by **mike.perry** » Mon May 04, 2009 8:55 pm

The heat shield I have in my Traveller Midget set up is just a sheet of ally cut out to fit the carb mountings It is standard Midget setup and holds the ends of the return springs.

Post by **alanworland** » Tue May 05, 2009 10:48 pm