Another 1500 SU Needle Thread

[CharliesStag]

My Spitfire does go fine, but it is not what you would call quick.  Granted I am used to the pace of the Stag and previously the Sprint, but I am sure my Midget 1500 had more pep than this car all those years ago (and that was in standard form).

Whilst I admit the points could do with changing (it starts and runs a tread mind you), it just is as flat as a pancake about 3kRPM.  Whilst I admit they are not keen revvers I did expect a little more than this.  Initially when I bought it was undrivable above 2.5k-3k (it would go on and then almost pulse in power).  Fiddling with the carb enrichment has finally got me to where the car is now (more driveable).

FWIW the spec is a reconditioned engine, which is on a 4-2-1 exhaust manifold (on a stock 1500 backbox), complete with K&N Air Filters on ABT needles.  The HT Leads (Unipart) and plugs are relatively new.  Fuel flow is fine too as is the ignition timing which seems to advance as it should according to the strobe light.

I have read that the needles are probably not the best choice on my car, with people suggesting either AAQs or AARs for my setup.

So, for a stock 1500 on a tubular manifold and K&N Air filters what would be your needle choice?

[Bainzy]

With ABT needles I'm not surprised it's flat, they're nowhere near rich enough. I'd go with one of those two needles, and also change the springs in the carb dashpots for heavier, yellow ones.

For me, I needed something even richer with K&N's and 4>2>1, but then I've got a single large bore exhaust, Megajolt and an 88c thermostat as well.

[sparky_spit]

I'd say AAQs are about right.  One rough guide to checking if you want richer needles or not (and it is rough....) is to use some choke while accelerating through the flat spots/poor performnce area.

I don't mean just pulling it out fully, but doing some checking first to see how much dashboard knob travel you need to get to the point where the jets start to move downwards, and also how much extra you need to move them a couple of millimetres at a time. Then go out on the road and try it several times as you accelerate and see if performance improves or not.

It's not going to tell you what needles you need, but it will give you an indication of whether you need richer ones or not.  Ideally you need a rolling road session, see Paul B's thread on 125 Distributor in his 1500 Spitfire.

[CharliesStag]

I think I did try the choke method although it did not seem to do alot strangely.  Mucking around with the mixtures yielded better results (although the carbs were way out of balance when I bought the car).

Cheers for the above, I have ordered a set of AAQ needles and will see how I get on.

Another chap has suggested I go for AANs.  Or are these overkill for a stock 1500?  

FWIW, mine also seems to be a large bore exhaust, until the backbox (the receipts show that the car once had fitted a Rimmer Bros 'Loud' twin exit system, but of that, only the centre pipe and manifold etc. remain, with the backbox being a quieter unit (I can only guess the exhaust became tiring for the PO :))).

[shedmonkey]

For what its worth I have home made air box with remote filter,tubular manifold and a home made 2" system to single rear box running ATT needles- seems spot on

[CharliesStag]

Well, I acquired a pair of AAQs in the end, and I must say after fitting them and tuning the engine (it was inevitably running richer after I initially fitted them they seem to have done the trick :).  It seems much more linear across the range, with it pulling happily above 3k (not that you would wish to with a 1500 mind you!).  I do however now have a spare set of ABTs with less than 2,000 miles on them...

Not quite as quick as the Stag I admit, but it is now quite a fun machine especially with its suspension setup :).