carb setting

[peter f]

Hi everybody - all the very best for Christmas and the New Year.
I have recently fitted new needles to my carbs, and it performed well on our recent 'last blast' returning 20 mpg in mixed driving conditions.
I screwed the needles right in, and backed them off one and a half turns anticlockwise, and it ran well.
The thing that puzzles me is: does it follow that the more you screw the needles out, the more mpg you get out of the car, providing it runs well when you do.
When I first fitted them, I backed them out two full turns, and while the car went ok, the plugs were very pale (going on white), so obviously sounds too weak a mix.
Any advice from those who know would be much appreciated.
have a good 'un !!
Peter

[Guest]

imported post

Hi Peter, when you fit the needles, you need to adjust them so that theneedle holders areflush with the base of the piston, like a "T", then wind them up a quarter turn,winding them to the end of the thread then counting back won't always work, one thread may be different, or worn,thenrun the car, if you have no gas measuring kit that's the only way to judge, it's critical that both needles start at exactly the same position, and are adjusted exactly the same amount,and the carbs properly balanced. Shout if you need more help ! Martin.

[peter f]

imported post

Thanks Martin, I'll whip out the pistons over Xmas, and start with them flush at the bottom.
Am I right in thinking that the more you can back them off, the better economy you will get - so long as the car still runs ok?
cheers bud,
Peter

[Guest]

imported post

Hiya, basically, yes, winding anti-clockwise lowers them, weakining the mix,but you get to a point where lean runningmay contribute to an overheating problem, also, running lean can need more throttle to produce the same power. If you can get to the point where the plugs are a light biscuit (brownish) colour it's about right.

To be fair, you can't really tune the CD175s for economy, only efficiency, the rest is largly down to driving style and distances covered, e.g. on a run to Switzerland in '05 at speed on motorways, my old girl did 31 mpg, good for an auto, short journeys, not properly warmed up, results in about 18 mpg. A bit of a compromise. Martin.

[V Mad]

imported post

This graph explains it all. You can tune for either best economy or best power or somewhere between the two. As Martin says if you go too weak you can cause damage to the engine.