just back from the dyno. running lean

Hi everyone,

Went to the dyno this morning with my '76 gtb. We started doing a pull and stopped at 5200 rpm due to how lean the car was running. From 2500-5000 it was running at 15.4:1 and we stopped right at 5200 when it hit 16:1. Who knows how lean it would have been if we continued. It did hit 156bhp at 5200 and 157 torque prior to stopping.

I know I have stock main (135) and idle jets (55), so should I get a set of 140 mains and 60 idles to clear this up? Or should I look for another possible issue. BTW, I just replaced my plugs and air filter.

thanks in advance- john


one more thing. I had the car weighed right afterwards. With a quarter tank of fuel and me not in the car, it weighs just a few pounds over 3000.

 

Should I go a size larger with my mains as well as the 200ac?

 

As-weighed configuration is as follows:

-original 1976 steel US car with US bumpers

-all emission and evaporation equipement still installed

-tool kit in the car, but not the jack kit

-1/4 tank of fuel.

Car was weighed at a truck weighing station and is advertised to be accurate within 25 pounds. The printout they gave me shows 3000 pounds flat, but when I asked for a more correct number, they said jsut a few pounds over 3000 came up on their screen.

 

air injection stuff was disabled during the run.

 

Just got off the phone with Mike at Pierce manifolds. He advised I run a 190ac with 145 mains and 60 idle. Pretty big main.

 

the timing is spot on. I just changed back to points (call me old fashioned), recurved both distributors to correct spec, and running NGK BP6ES. the engine has 170-175 compression on each cylinder

 

I was highly surprised about the weight. I know that the scale I used is pretty accurate due to how many cars I have weighed there, and then confirmed the weight on professional auto scales. For instance, my '86 Porsche carrera weighed in at 2750. I later weighed it on pro auto scales and it came in at 2746, so I assume the Ferrari wiehgt is very close.

Regarding the jets, I ordered a TON of jets. 8 140 mains. 8 145 mains. 8 190 air correctors. 8 200 air correctors. 8 57 idle jets. 8 60 idle jets. 8 34 mm chokes. I am going to hit the dyno for a full day and post the results of what several setups run so people will finally have a reference point with hard numbers regarding bhp, and mixture. I understand each car is going to be a little different, but this may be a good baseline.

 

Actually, I ordered all my jets from a colleague in Europe for $1.90 each, and the dyno time is done at a friend's shop.

 

Good to know about the chokes. I was advised by Carobu to try 34mm chokes. Sounds a bit big to me too, but this is more academic than anything else.

 

The air pumps alone would be 30lbs. I don't have the heart to replace the US bumpers with Euro style though. I would be too afraid if someone accidentally bumped me.

One key fact I did not even think about that I should have mentioned. My exhaust is a light ansa sport, and my rear valance has been modified to the Euro look./ I bet that saved a ton of weight.