[TR] TR3A SU H6 Carb Rebuild Question

David Griffiths daveg at online.no
Sat Sep 8 17:05:20 MDT 2018



> On 08 Sep 2018, at 18:46, Paul Dorsey <dorpaul1 at gmail.com> wrote:
> 
>  My memory does work At 
> times and I have a head injury!
> 
>  Jim H.   May need our guidance. His original question was that he set his at  One and a half flats  and that’s wrong. It should be 13 Flats. I am i right or what?
> 
Hello all,

I rebuilt my carbs last year including rebushing the throttle shaft, and yes, the recommended initial jet setting before tuning in the manual was to tighten the jet-adjusting nut up until it stops, then turn it out 12 flats (2 turns). 13 is pretty close to 12. But you need to then adjust the nut for you own car by just experimenting the nut up or down a flat or two at a time and see the effect on the mixture and engine behaviour. Different people like the mixture a bit more rich or a bit more lean. To gauge the result of turning the nut, you can use a hand-held tachometer to see if the engine turns faster or slower, or lift the carb. piston a 1/16” up or so - same thing, faster or slower. I used a Gunson colortune and could clearly see the flame colour turn from yellow (too rich) to blue (neutral) as i adjusted. I took it down to a bit too lean at one point, but you can kind of realise this from the engine’s behaviour. 

There is of course also the adjustment to balance the two carbs by using a suction meter or testing the height of the carb. pistons using the SU toolkit, and then the idle speed. Before my rebuild, idle was hopeless and unstable under 1000rpm. After - beautiful even idle at 600, plus a tank of petrol lasts a lot longer. 

Dave


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