Air / Fuel Ratio

cobraboy

Well-Known Member
Today I found an Air / Fuel ratio meter that I had misplaced for some time, as I had put in lambda bosses in the exhaust when I built it I thought I would try the meter on the car.
It is not an expensive one, and previously I had not had a lot of luck with it, but it seemed to be putting out sensible info. To start with idle was rich, and you could smell it was. I gradually got it in range (mid scale) then took off the dashpots and equalized the jets down from the bridge with a digital Vernier, tried again and a couple of goes later had the AFR where I wanted it with equalized jets.

At cruise on the road it sits around mid point, but under hard acceleration goes lean. I looked in my jet book and see that BAM offer an small enrichment over the BAW I have in, so will order a pair and play.
Pic at idle.
IMG_1592.JPG
 
Interesting. I finally got the KPs in instead of the KOs and the car is transformed. No missing, no hesitation. Mine is a standard 10.5:1 on 98 unleaded with a slightly more aggressive cam. Overall I think its a little rich but when I get my freer air filters in that should balance it out. But all guesswork of course.
 
Peter
I have HS8 on a 4.6 ;)

The reason I wanted to check it is I fitted larger freer flowing air filters.
 
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My point was the standard setup is marginal on 5 star leaded - clearly the V8 was set up for economy from new. I think as Chris York discussed, pretty much every P6 runs lean these days not just because of lead but the very different formulation of modern fuel. But I'll only know when I do the exhaust side too and fit similar bosses to yours. Oddly, the car smells much better. Usually rich mixtures smell of unburned fuel, I can only conclude some of the cylinders weakened so much before I was getting misfiring.
 
Yes they are thanks :)
I have fiddled and faffed for many hours experimenting with various weights of springs and viscosities of oil.
I ordered the BAM to try to richen the range from cruise to WOT.

I should just shove on the 4 barrel I have, but the SU's are so nice I just want to get the absolute best out of them before trying another carb.
 
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BAM needles arrived today, they made a small difference, but engine is still way lean under hard acceleration. It must be getting loads more air with the new filters.
I have realised that the only way I am going to get it right is to modify my own needles. I have been sanding an old pair of BAW in a cordless drill, marking the needle every 1/8" and measuring each graduation before and after sanding. I always thought it was a black art practiced by blokes in brown store coats and flat caps, but to my surprise it is yielding results, I have called it a day now, but the car is responding, little by little the mixture is becoming richer in the area that I need it to. The acceleration is also becoming more urgent.
I really need to decamp to an airfield and play all day with it, coming and going from home is not ideal on a bank holiday weekend.
 
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