Vitesse MK2 needles for modified engine Chapter 2

[Iain T]

Chapter 1 is deleted as I wasted a year piddlin' about with various needles, damper springs ratings and damper oil viscosities only to find the refurbished carburettors were not assembled correctly. As my other topic on the forum says the bushing was above the carb body bridge. Once I had solved the problem by fitting the correct thickness washer the mixture was very different. As suspected the bushing shrouded the jet and caused the pick up of fuel via the rush of air to vary significantly.

I've tried the 6J, 6S, 6A and 7B needles with all the spring/damper oil variations (a lot of carb fiddling) and the winner is the 7B.

All the others including the standard 6AC have issues with mainly leaning out at high revs or mid/high acceleration. I can get a decent tick over on all the needles but on driving with my telltale AFR meter and feeling how the engine performs it's only the 7B that gives anywhere near a drive able car. It does get rich at low revs so I've fitted soft 55g damper springs to try and raise the air piston a bit but I'm not sure there is any gain over the standard 100g springs especially when the spring is not that compressed as is the case at low revs. I need to do a longer run but traffic today is crazy as usual. On the upside I've learnt a lot about Strombergs and the theory of constant velocity carbs!

So if you have a sorted gas flowed head, 631 exhaust, K&Ns etc what the book says is correct 7B is the needle of choice. It must have taken me £150 of parts and the same in petrol to come to that conclusion..... I attach a chart of the needles I tried with the 13 stages of taper.

I'll post the afr readings after I've been for a long varied drive.

Iain

 

Edited June 5 by Iain T

[Colin Lindsay]

I'm currently selling a single unused spare Stromberg carb and on checking it prior to listing found a pair of 7B needles from my old Mk1 GT6 stored with it, they were the only ones that gave a decent drive out of the alternatives I tried, so were my preferred favourite for the basic setup. 

[Iain T]

My test were forgive the pun exhaustive. I've lost count of the variations I've tried but the only driveable option is 7B. They aren't specified for a standard engine so perhaps your GT6 was modified?

Iain

[Colin Lindsay]

19 minutes ago, Iain T said:

My test were forgive the pun exhaustive. I've lost count of the variations I've tried but the only driveable option is 7B. They aren't specified for a standard engine so perhaps your GT6 was modified?

Iain

I had fitted a tubular exhaust manifold, but that was the only real upgrade. The carbs were supplied refurbished by Andrew Turner way back in the day, so that's the needle he fitted before returning them to me. I sold on the original carbs once his were fitted, however the sole remaining carb was a leftover and I reckon I just copied the needles that he had fitted with no problems at all.