Changing Needles And The AFR

SydneyRoverP6B

SydneyRoverP6B

Well-Known Member
Staff member
Following on from my post on cylinder heads, standard or modified, it also makes very good sense and indeed follows established scientific principles to take the same approach with carburettor needles.

Obtaining an air/fuel ratio printout is the perfect way to receive information on how close or not your existing needles are to being largely correct. Swapping needles without such information is like driving with a blindfold on.

Ron.
 
it'd be interesting to weld a lambda sensor into the downpipe and monitor it vs throttle position. Of course you're almost at the point of single point injection then ;)

Rich
 
I welded one into the LH collector and I must say it is very useful when tuning the carb.

Also makes a good dancing dial on the dash :D

Richard
 
I have an air/fuel ratio printout for my Rover's original 3.5 litre engine which I'll post up in a few days time.

Ron.
 
Below is an air fuel ratio printout for my Rover's original engine, which was fitted with the P6B air canister, free flowing foam air filters and a single skin stainless steel exhaust system. The needles were the factory specified BBG. As can be seen, under acceleration, the air fuel ratio runs from a minimum of 13.8 : 1 down to a richer 12.5 : 1. The ideal for an acceleration mixture is 12.5 : 1, which will deliver the strongest possible acceleration in the shortest possible time.

Accompanying the air fuel ratio printout is my Rover's original delivery of power to the rear wheels, which was 69kW (93HP). Considering that engine had over 203,000 Miles (327,000km) upon it, the timing was set to a very inefficient TDC at 600rpm, and the camshaft (some lobes were worn down by 3mm :shock: ), lifters and timing set were all shot, the power wasn't really too bad.

The black air fuel ratio printout which is largely linear is for my 4.6 after the needles were polished to suit the engine. Here the minimum is 12.8 : 1 quickly dropping to 12.5 : 1 where it essentially remains.



More to come!

Ron.
 
You must log in or register to reply here.
Back
Top