Re-profiling an S U needle

[millerman]

Have just fitted a 1275 Midget engine running a HIF 44 carb, I have adjusted the jet and the engine pulls well but seems lacking in power at very low revs ie hesitates slightly when pulling away

NOW, any advice for using emery cloth on the needle where it goes into the top of the jet at idle. Would I need to rub down the needle for half an inch or so in this area?

Thanks for reading

[panky]

I had similar problems on one of my campers that I did an SU conversion on (HIF44) I just took the needle out and filed a small flat with a needle file (so that's what they're for) right at the top of the needle. It improved things quite a bit but I think it needs a little more.
It's good because you can see exactly how much metal you are removing, with emery it's guess work and practice.

[bmcecosse]

Nearly all the needles are the same profile for the first few steps -but no harm trying it, except risk of scrapping the needle of course. I suggest using EP90 in the dashpot as a first/reversible try... It works for my car! BDL is the general 'starting point' needle for a modified 1275 engine - or is your engine standard ?

[mike.perry]

A book of SU needle charts will show you what the needle looks like before you start filing it and you might find one that suits your needs.
http://www.mintylamb.co.uk/suneedle will plot and compare the profiles

[bmcecosse]

Indeed - but at IDLE they are all the same...or very nearly so... If the EP90 doesn't do the trick - then the answer is to richen the idle - and perhaps select a weaker needle for further up the range....if necessary.

[millerman]

I have not tried the EP 90, perhaps BMC can post me a table spoonfull but I did top up the carb dash pot which improved things a little.

Fuel consumption, 1275cc with HIF 44 carb, around 30mpg on a long run keeping up with nearly all the moderns. Local journeys and towing 8cwt trailer much worse

Plug photo shows the mixture is about right[frame][/frame]

[bmcecosse]

Seriously - try the EP90 (or 75/80 if that what you happen to have in stock)....