next... AFR readings,

[Mr 5]

ok so now the car runs,JOY!

next,understanding the AFR, ok so on idle its 12.8,normal driving 14.8,flat out, full boost, 12.2-13.1

guessing over 14.something is lean,under is rich, so am i safe running as it is or does my carb need different size jets? running 1.1bar at manifold if that makes a difference?Aready fitted a larger boost jet and i know the carb was fiddled with befor i got it,looks ok to me but i could be wrong,it happens alot!:scared::sad2::ashamed:

[Andrew Cooke]

13 is a bit lean at the top, the rest is Ok, although you should be able to get the idle a bit better, ie nearer to 14.

[Mr 5]

just been out again, idle is 14.9, no idear where 12 came from?! gremlins i tell thee!

so what can i do to get it lower than 13?other than turn the boost down? larger boost jet maybe?

[Scoff]

maybe you had the choke on when you got 12.8 idle ? you want the engine hot and with no choke before you read or set idle.

[Andrew Cooke]

ooh, what's a boost jet? I like the sound of them.

it kinda depends what you mean by 12.2 to 13

is it 12.2 at low revs and 13 at high, or does it start at 12.2 then just go to 13 over time?

it really helps when you can log AFR against RPM and boost, a hard acceleration through the gears (like at a drag strip) tells a lot about what's going on.

[Mr 5]

just using the 'lingo' i heard on the 'street' ,innit;)

im racing at york next weekend,so il log the results and have a look back over them, what sould the AFR reading be when on boost?i noticed when the car gets to the top end of the rev's the fueling must die off because the gauge reads 14-14.9

[Andrew Cooke]

that sounds dodgy, you need to sort that before you break it. Check your pump and filters, going lean with time is a fuel supply problem.

[Scoff]

a rule of thumb: do a pull in 4th gear - if it leans out slowly from 12 upto 13+ then try a smaller air corrector. If it holds stable until, say, 5000rpm and then climbs lean pretty quickly then the carburettor bowl is emptying too quickly so you'd want to check fuel pressure and try a larger needle jet if pressure is OK.

[Andrew Cooke]

a rule of thumb: do a pull in 4th gear - if it leans out slowly from 12 upto 13+ then try a smaller air corrector. If it holds stable until, say, 5000rpm and then climbs lean pretty quickly then the carburettor bowl is emptying too quickly so you'd want to check fuel pressure and try a larger needle jet if pressure is OK.

I'd ruled out the needle jet with 1.1bar boost, was I being a bit 'asty?

[Scoff]

no, but notice how I included fuel pressure in there also :)

[Andrew Cooke]

no, but notice how I included fuel pressure in there also :)

I did, and now you're going to have to explain how to check it, and what to look for. I on the other hand neatly avoided saying anything :laugh:

again:coffee:

[5teve L]

I did, and now you're going to have to explain how to check it, and what to look for. I on the other hand neatly avoided saying anything :laugh:

again:coffee:


Lol...

[Mr 5]

ok been out again,yeh on idle its not 12.8 :******: , its more like 16

on full boost its between 11.9 - 12.6, thats the max and min it goes to all the way to 6k rev's, which is as high as i ever take it, and just chilling at 30 its 15.0,70mph its 12.9,

seem's ok to me, but i realy know nothing,that sound about right?

[Miller]

This is how i would set it

Idle: 14:1........any leaner and it will pop on over run :D

At cruise speeds: 14:5 - 15:5 @ 70-80mph

On boost: 12:0 - 12:5 but no leaner

Hope you get it sorted mate :)

Chris:)

[paul b]

ooh, what's a boost jet? I like the sound of them.



we do them, Group A ones though .....
we supply them free with 20ltrs of our SPECIAL Derbyshire oxygen/hydrogen race air mix...



NOT