time old afr questions......

[fatroofer]

Really sorry guys but I'm honestly not that clued up when it comes to reading my wideband! I'm sure a lot of you probably get sick of hearing the same old questions about afr's etc........ but I have had a look at a number of posts (mostly on the other site that shall not be named!) and some of the responses differ drastically! I understand also that each engine will have a sweet spot (of sorts) and what is right for one car may not necessarily be perfect for another, what I need to know ideally is good and bad extremities of afr readings...
My spec is;
Full T25 on 15/16psi
Breadbin int
Phase 1 fuel pump
Bms d/p
Zeitronix wideband

The boost kicks in at around 2.4k and full boost by around 3.5k

Readings at present are
Idle @14.5
Cruising @13-14
Part boost @10.5
Full boost @14.5

It's this last stat (full boost) that worries me, thought it was quite lean......
Thoughts appreciated gents, and again apologies for the naivety!

Steve

 

[andybond]

Thats incredibly lean buddy. Back off the loud pedal and rejet to suit.

 

[andybond]

( and sell your BMS downpipe and buy one of ours. )

 

[fatroofer]

Unfortunately I am not au fait with the dark art that is carb jetting/setting up...... looks like I will have to wait till I can get someone I trust (and cheap) to do it!

 

[fatroofer]

( and sell your BMS downpipe and buy one of ours. )

Will do mate!!!! £400 and it's yours!!

 

[andybond]

Unfortunately I am not au fait with the dark art that is carb jetting/setting up...... looks like I will have to wait till I can get someone I trust (and cheap) to do it!

Where abouts are you in the UK ?

 

[fatroofer]

S/E London

 

[fatroofer]

I would ask Matt (code red) but I know he's got a lot on with the move and everything at the moment, I know Marky Mark is supposed to be good but it's just getting there (and the time).

 

[Brigsy]

Way too lean on boost, you need to be 11.5-12.0. Make the 2nd stage jet bigger 1.3mm, if that is not enough make the air corrector smaller for more fuel.

 

[Number 11]

sounds like you have a standard carb???? 15 psi is small time boost increase and is only the start.... you have a turbo that isn't being pushed.... 130 / 1.3mm main jet fitting if not already, is a good start..... its a piece of cake to up jet a these solex carbs..... 2 x 12mm nuts hold the carb down , once removed the 11mm screw head with a copper washer facing the rocker cover will reveal the main jet inside the body of the carb....with a medium size flat screw driver.. lower the carb body down onto the driver which should be straight up... once unscrewed the main jet will balance on the driver and the carb body can be lifted off the driver with the main jet on top of the driver... refitting is the reversal of removal... the new main jet should be balanced on the screw driver upright... then lower the body onto jet and screwdriver... a couple of screws up an it done.... then refit the carb ,, and check afr's on boost... if you really want to give it a bit more of a boost, use a 135 main jet and turn the boost up to 18psi about 170 bhp..... simples.................. and I find the best buy for jets are from Mike at GT Spares.. if you don't have pre drilled units to hand .....

 

[fatroofer]

Cheers for the replies fellas, pretty much what I was thinking! I've order a 130 jet and a 135 (just incase) from southern carbs, once they're here I'll decide whether or not I'm feeling brave enough to do it myself or get someone to do it for me.....

Will it still be ok to drive til next weekend? (obviously leaning off the loud pedal)

Thanks again guys

Steve

 

[andybond]

Wind the boost RIGHT down.

You will need to change the air corrector as well I guess.

 

[fatroofer]

Wind the boost RIGHT down.

You will need to change the air corrector as well I guess.

Thanks a lot @andybond! I'd just about summoned the confidence to tackle this myself and then you go and start talking all Chinese to me!!!!! Anyone got Marky Marks number??

 

[andybond]

You will be fine.

You make the air corrector smaller to make it richer. Its another brass washer jet.

 

[Brigsy]

You should be ok with stock main jet..changing the main jet only is very oldskool. I wont repeat my post above

 

[fatroofer]

Thanks again fellas, great club=great help! I will wait for these jets to turn up and probably try to tackle it myself.... I'll see how it runs with changing the 2nd stage before toying with anything else! @andybond @Brigsy @Number 11

 

[Number 11]

the second stage enlargement is a good part of the solex carb......... but I haven't had much success above 1.2 mm enlargement and unless your rebuilding the carb with replacement seals for the second stage block to hand I wouldn't take it off........ I have found that people who lean the cars off too much with only second stage and air corrector adjustments have a quicker car but wind up doing a head gasket.................. I try for richer fuel ratios, because when your gunning it down the motorway or pushing the car for a while , the extra heat will cause a change in the combustion chamber from charged air temperatures..... taken up by the slower burn of the richer mix ..... as a carb It will never have fuel injection quality control.....


Best try both or one at a time....... try the second stage in increments...once opened up the block is hard to reduce ....

Renault used a larger main jet in the phase 2 over a phase 1 ....115 to 120.... Very old school

 

[fatroofer]

the second stage enlargement is a good part of the solex carb......... but I haven't had much success above 1.2 mm enlargement and unless your rebuilding the carb with replacement seals for the second stage block to hand I wouldn't take it off........ I have found that people who lean the cars off too much with only second stage and air corrector adjustments have a quicker car but wind up doing a head gasket.................. I try for richer fuel ratios, because when your gunning it down the motorway or pushing the car for a while , the extra heat will cause a change in the combustion chamber from charged air temperatures..... taken up by the slower burn of the richer mix ..... as a carb It will never have fuel injection quality control.....


Best try both or one at a time....... try the second stage in increments...once opened up the block is hard to reduce ....

Renault used a larger main jet in the phase 2 over a phase 1 ....115 to 120.... Very old school

Sorry, I meant main jet (as per your first post) like I said, fairly new to this......

 

[Number 11]

Yo Fatroofer....... thanks for the posts................... of course we all started as new owners to the mighty GTTURBO,
I've just bought my 8th... I cant believe it......

years ago I would drive all the way to BBtuning , have the car on the rolling road and have them fit a £3 jet..... and cost about £100..... what a sucker......

some people think opening up a carburetter is some king of mega skill.... it aint if you have common sense .. some people are scared to give advice in case the car blows up

with a 5 gtturbo you can take a standard engine from the 120 bhp to 240 bhp for not a lot of money the largest expense could be a T28 hybrid turbo.......

as you have an Air Fuel Ratio meter in the car , you could , if not already buy a second carburetter, clean, rebuild and open up the fuel chambers ,and have a good mess about..... buy a stethoscope and run a line of rubber tubing from the head or block into the car and listen for the tel tale sound of pre-detonation , driving on gravel ... and get over 200 bhp from that good turbo...... years ago so many people tuned cars this way ,Halfords sold stethoscopes ..........

 

[6foot6]

Really sorry guys but I'm honestly not that clued up when it comes to reading my wideband! I'm sure a lot of you probably get sick of hearing the same old questions about afr's etc........ but I have had a look at a number of posts (mostly on the other site that shall not be named!) and some of the responses differ drastically! I understand also that each engine will have a sweet spot (of sorts) and what is right for one car may not necessarily be perfect for another, what I need to know ideally is good and bad extremities of afr readings...
My spec is;
Full T25 on 15/16psi
Breadbin int
Phase 1 fuel pump
Bms d/p
Zeitronix wideband

The boost kicks in at around 2.4k and full boost by around 3.5k

Readings at present are
Idle @14.5
Cruising @13-14
Part boost @10.5
Full boost @14.5

It's this last stat (full boost) that worries me, thought it was quite lean......
Thoughts appreciated gents, and again apologies for the naivety!

Steve

Stick a 135/140 main jet and swap the air corrector round.

Job done.
Perfect for 16psi.

Tuners used to charge mega money for a 10 min job.

You can do other things with the enrichment side, but not worth it.
Rather have it a little rich, a carb will never be as bang on as efi..
Suited me fine in my 5 GTT and 11 Turbo , both hit 155/165BHP at 16PSI with a T2/T25 back in the day, good for 14.5 sec 1/4 miles, never popped a HG. There is a great book by Haynes CARBURETTOR MANUAL - SOLEX, WEBER, FORD & PIERBURG. - HAYNES TECHBOOK No.3288, did me proud