V8 conversion poor running

[DFR]

I have recently converted my landy to 3.9 V8 on  SU carbs. The carbs and manifold were off a 3.5 so it is running poorly. Has anyone else done this conversion and know what number needles they are using as I have been reliably told that this is the main problem, unfortunately there are lots of different ones and cannot seem to get the information on which to replace them with.

Cheers Dom

[V8MoneyPit]

The problem is that the 3.9 never had SU's as standard, so there is no needle spec readily available. The main differences will be relating to compression ratio, cylinder head ports (I seem to remember the 3.9 heads have better ports), air filter type and exhaust manifolds/system. Basically, anything that changes the engines air consumption will affect the needle requirement.

You will need to establish where it is running weak and/or rich and specify needles to correct this.

There used to be a nice little programme called WinSU available for download. You can compare needles in a graphical form, so if you know your existing needle needs to be richer at the top end, for example, you can click through alternatives until you find one that does what you need.

HTH.