fuelling problems

[jonnyshaw49]

hi i was having problems with my car idling before, and i have just fitted my new t25 and wideband, started the car and the car wont idle unless guage is reading 1500 rpm, new mixture screw fitted and wound out 2 and half turns from fully in, the car hunts between 1000rpm and 1500 rpm, and wideband guage is moving from 15's to 17's, can anyone tell me what this could be?? i was having problems with fuel dripping down venturi , so rebuilt carb new gaskets and it seemed to stop dripping, another thing i notice is when i rev the car the wideband reads between 11's and 13's then gets higher, then when i let of the wideband reads 17 and wideband guage goes off because its above 17.7 and guage cant read it, the carb has standard jet in at the moment and the turbo is t25 but would it still show it running lean at idle?? any help appreciated thanks

[HULK]

I have the same problem as you buddy but I'm at the other end of the spectrum and I have afrs of around 10 which is stupidly rich. Still don't know why it's doing it. May have to try a diff carb.

Obviously your running too lean. Wind the mixture screw out till your idle afrs are at around 14

[jonnyshaw49]

so idle should be around 14?? but mines idling at 1500 not 1000 so should it be different to 14?? thanks for the help

[Markey Mark (BD)]

As mentioned before wind the mixture screw out abit more and then bring the idle screw down abit to bring the revs to around 1000rpm. Check the afr's while your doing it too mate, try get it around the 14.5 mark

[jonnyshaw49]

i tried doing that earlier but winding mixture screw made no difference hardly, but ill have another go later and let you know.what jets should i be putting in to take this t25 hybrid?? want to run around 20 psi, thanks

[Markey Mark (BD)]

i tried doing that earlier but winding mixture screw made no difference hardly, but ill have another go later and let you know.what jets should i be putting in to take this t25 hybrid?? want to run around 20 psi, thanks

It should make some difference agjusting the mixture screw mate, did you do it with it running around 1500rpm? If so do it with the idle at 1000rpm.

Only way to know what needs moding on the carb is to take it for a drive at 20psi and see how it fuels then adjust it from there, obviously if you see it lean off too much back off, modify carb then try it again.

[jonnyshaw49]

ok mate will try the 1000 rpm , i have an aftermarket rev counter to fit to see if the original is out , what is too lean in afrs?? thanks

[Markey Mark (BD)]

If its running 15's to 17's then yes mate too lean

[jonnyshaw49]

hi just been messing with my carb, i have wound the idle screw down to 1000 rpm but for it to idle with 14's on wideband the mixture screw is out 8 and a half turns, instead of 2 and half turns, why could it need to be wound out so far, then if i slowly rev up the car watching the wideband right upto 3.5-4k the wideband stays at around14-15 then from 4k to 6k it goes back down to around 13's so why would it start to run richer again at higher revs??anyone any ideas

[Markey Mark (BD)]

Do you know the spec of the carb?

I find that larger venturi carbs normally need the mixture screw to be wound out further than standard.

To be honest not every 5 has the mixture screw wound out 2 1/2 turns, some standard ones i have done needed winding out 4 times. If its running and fueling nicely on idle i wouldn't really worry too much.

[jonnyshaw49]

it sounds really lumpy mate, when i rebuilt the carb it seemed to be a standard venturi, why does the mixture richen up though at higher revs, also the car will not run unless i start it with choke untill its warm and fan kicks in, then drop the choke and it will idle, surely that cant be right can it??

[Markey Mark (BD)]

it sounds really lumpy mate, when i rebuilt the carb it seemed to be a standard venturi, why does the mixture richen up though at higher revs, also the car will not run unless i start it with choke untill its warm and fan kicks in, then drop the choke and it will idle, surely that cant be right can it??

Is it lumpy on idle?

Best way to find out what size venturi it has is to measure it, they all are machined from the original 25mm one so will have 25 stamped on there which makes people think its still 25mm

So its running rich when driving it part throttle? Prob been jetted then if its richening up mate.

Sometimes 5's need alittle choke to start them up from cold, i've not know one need it till fan kicks in only really till it starts to get warm then they idle fine. Some don't need choke at all.

[jonnyshaw49]

yeh it hunts slightly on idle mate, it doesnt have any bigger jets in mate as i out them all back standard, the venturi had 25 stamped on it, but if it was machined bigger wouldnt i be able to see the machine marks??? can i swop the venturi from another carb or is it a big job??

[Markey Mark (BD)]

yeh it hunts slightly on idle mate, it doesnt have any bigger jets in mate as i out them all back standard, the venturi had 25 stamped on it, but if it was machined bigger wouldnt i be able to see the machine marks??? can i swop the venturi from another carb or is it a big job??

No not neccessarily see machine marks on the venturi mate if its been machined out.

Yes you can remove the venturi mate, need to pull the carb base off and you'll see a small aliuminium cylinder holding the venturi in, pop that out and from the top knock the venturi out. Will be abit tight so be carefull with it not to break anything.