SLROC Forum

Currently putting plans together to upgrade the carburator on my Series 3, 2.25 petrol to SU carb.

I willmake a manifold adaptor to fit the SU carbs.

What SU carburator is best suited HS6 or HIF?

What angle should they sit, 30deg?

Any other advice before I start?

Thanks

why not fit a new weber, kits are easy to come by rather than make something fit

From what I have read so far, webers are good for economy but the zenith that is currently fitted is a better all round carb for the series 3.

 It is a matter of opinion  on the Weber and the debate never ends.  If you check out ACR tuning, you will get an idea what SU is used to optimally suit The 2.25. SU is good.  I have had Weber and Solex.  Nothing wrong with Weber and you get a brand new carb for not much money.

ACR kit contains the HS6.

In the "good old days" converting the 2.25's to SU's was the conversion of choice for various reasons, a couple being:

Moved away from a throttle rod to a cable which meant no more accelerating as you wend down a steep hill in a trial and it was much more tuneable, replacement needles are available from Greenway Engineering if memory serves me.

The only downside was you have to put a shield around the adapter and the base of the carb otherwise it can freeze at road speeds in the winter

Bob

SU should be a HS6. If memory serves me correct a BAP needle would be a good starting point for setting it up. There's software on the net which lets you 'see' the various needle profiles. The standard air filter will need changed for a free flowing one (K and N or paper pancake type).

As mentioned above, SUs have a tendency to freeze up. The ACR adaptor has a feed through for engine coolant to give it some heat. A heat shield is a very good idea -  try to draw hot air from around the exhaust manifold. Reducing or blocking the air flow over the carb from the engine fan is also a good idea. Using a fuel treatment like Silkolene pro FST also helps.

The carb is angled about 30 degrees from the vertical.

Hope this helps.