Twin Carb set up

Post by **youngun** » Tue Jun 26, 2007 10:55 am

If i were to get hold of a midget manifold, would i be able to build a twin carb set up, as i have 2 spare HS2's.

Or would it be a lot of work for little gain?

Thanks
YG

Post by **alex_holden** » Tue Jun 26, 2007 11:04 am

I suspect a single 1.5" carb on a decent manifold might perform better. Remember on a 4 cyl 4-stroke there's only ever one cylinder at a time drawing in fuel/air.

Post by **youngun** » Tue Jun 26, 2007 11:05 am

Aye, The HS4 has gone off to a friend who is fabricating a Stainless big bore manifold for it.

Post by **Orkney** » Tue Jun 26, 2007 11:17 am

breathabilty is the biggest factor - an where do you stop the other.
Theres no point throwing excess in if it cant get out - had a rally mg metro some years ago (ok a lot of years ago) ended up with pair twin webbers so effectively 1 carb per inlet port - stage II or III head (cant recall which) so it could get in and out faster - then a competition exhaust which was 4-2-1 meaning all that extra burnt fuel could get out quickly enough.
Then the appropriate camshaft to make maximum efficiency of the combustion cycle. It was a pig to start from cold but was an absolute beast when running compared to the standard configuration.
A very good read is tuning the A series by David Vizard - dont look at it if youve spare money or a craving to go faster though !

Post by **Stig** » Tue Jun 26, 2007 11:38 am

You won't get a lot more flow from twin carbs as has been said. You'd likely get a performance increase from the manifold compared with the standard one as it's not got the exhaust heat reducing the inlet density,not that the Midget manifold is that good for gas flow according to the esteemed Mr Vizard. Setting them up can be a bit of a pain too if you want an idle speed below 1000rpm.
I'm assuming that you've got a left-right pair of HS2s, rather than two Minor carbs, and that you've got the linkages.

Post by **Willie** » Tue Jun 26, 2007 1:42 pm

The twin carb Midget manifold, known as the 'log' is extremely inefficient.

Post by **bmcecosse** » Tue Jun 26, 2007 1:43 pm

Forget the twins - stick with a big single - HIF 44 will be best by far.

Post by **Redmoggy** » Tue Jun 26, 2007 8:14 pm

Ive ran twin HS2 carbs for several years on my 1275. As far as performance goes id say it has a little bit more sparkle than with a single but thats about it. I keep them on because i love the induction noise with the 4inch trumpets and no filters!

As for setting them up i have to dissagree though. Do what it says on the tin (in the book) and they give no trouble and tick over lovelly.