Hello. I am tinkering with a '53 XK120 SE OTS. I was 'encouraged' to fit 2" HS8's and I am disappointed with the low down torque (ie off the line power) they have delivered. They are quite a bit better higher up the rev range but I really wanted to improve the off the line power.

It is a 3.4 with an SE head (not C type), both inlet ports reamed to 2". The engine was rebuilt 1000 miles ago. I have trumpets with foam covers. The needles are standard XJ6 BAW. Powerspark ignition.

Is there any way I can dig myself out of this hole. ? Maybe retard the ignition a tad ? Different needles ?


Any wisdoms gratefully received.

Keith

 

Hi, perhaps try a set of 3.4 needles, should be either BCC or BCX for the HS8’s, it might be running too rich at low speed. If you haven’t already done so I would put a decent timing light on it and make sure the vacuum and mechanical advance are correct through the rev range. Good luck.

 

http://solwayjaguar.co.uk/wp-content/uploads/2014/05/Fitting-2-inch-HS8-SU-Carbutettors.pdf

https://sucarb.co.uk/technical/technical-hs-type-carburetter-tuning-general

This article may be helpful
Rgds
David

 

Just for completion.

It turned out to be the Powerspark vacuum advance was faulty.
Replaced with a 123 ignition (GB) version and used advance curve 4.

All is well.