FCR carbs have issues with poor emulsion and they do not like smaller air correctors for that reason, I believe if you speak to Mark he will point that out, Bit of a bummer but normal jetting practice does not work so well with FCR's compared to say webers.

CV carbs on the other hand really need both the primary and secondary air correctors properly dialled in to work correctly, I had a Polaris quad on the dyno and despite a bigger float valve you could not get it running right too lean on top end no matter what main jet you used until you played with the air correctors which required modding the carburettor.

In the end it made more and better power on a modified stock CV carburettor than the HSR Mikuni that was on it when it arrived, the HSR is Mikuni's equivalent loosely to the FCR Keihin.

I kept the air correction jets stock on my 32/36's. I do have a air/fuel ratio gauge. Bought the simple one from Summit Racing. Has the red-yellow-green display. The 180 and 220 jets keep it in the green at WOT. Running a 110 Mallory Pump, 1/2 fuel line to the regulator and 3/8 to each carb. Since I'm only running an 1/8 mile at a time, it hard to tell mpg. Of course were talking apples to oranges here since I'm not running a A series motor.

Yes, there are 200 main air jets and I think 90 slow air jets. I experimented with the smaller air corrections but as described on the Factory Pro jetting guide for FCR carbs the just seemed to worked better with the larger air jets.

Tom

I was going to suggest a run on the dyno, just to check mixtures. I can't remember what jets I had in my A15, but I'm sure it was smaller than 165. You probably have big air corrections too, which gives the correct fuel to air ratio, but gives more fuel than the engine can burn. I'll try & get the carbs out of the shed for a look, but it's cold & wet here in Sydney, after a warm dry autumn(fall).

Engine makes maximum power somewhere around 13:1 to 12:1. You may find that leaning it out to 13:1 gives the same HP while using 8% less fuel

I pretty much wanted a reality check: I have 165 mains in the carbs which are not huge by any means. What I think is tripping me up is the vintage events are only 20-25 minute sessions whereas the track days are 30 minutes per session so the extra couple of laps is just enough to run the cell dry.

I'm hoping to get the car on a dyno in the next few weeks to see where it's at. I have procrastinated on installing an air fuel ratio gauge in the car for years. It's now our off season for the next 3 months, going to hit 107 F this week and won't go back below 100 till September. I'll get the A/F gauge installed over the summer.

I at least know I'm not way off, if Simon's 200 hp motor is getting 4mpg then my 105-110 whp motor getting 9 mpg sounds par for the course.

I come off turn 2 at 78 mph and 2400 ft later the car is up to 111mph, this up 9-10 mph from when I ran the A12 and was getting roughly 15mpg.

Tom

I seem to remember the A15 is a recent addition. The more power made, the more fuel burnt. So you might be spot on, especially as you compare it to the MX5 Miata getting about the same. The E85 fuel mentioned is an ethanol blend, so the cars run richer & get worse economy than pure petrol. Maybe you can find a bigger tank to make sure this doesn't happen. You could also go through the fuel system & check for fuel leaks. Nothing is worse than wasting fuel you really need. I think this is one of those things that seems like a problem but is just a change due to other things.

I'm doing a little better than sikyne with a rate of 6.1mpg with a similar but very docile A12 turbo running on E85 jungle juice compared to Simons beast.
More to the point ...who cares how much fuel we use in the race cars anyway??Got to be cheaper than sex

29 liter/50 km = 4.1 mpg (US)

I use about 7 gallons (29 Lts)in a 28 min race with the A12 turbo on E85. About 50 Kms. (23laps of 2.2Km circuit)