View Full Version : Carb fuelling
Jamie Eddolls
17-10-2008, 20:38
New poster! (less than 10 posts)
Hi All,
I just been reading the May issue of "performance tuner" the Renault 5 featured in the article has had adjusted fuelling on the carb ,so when he drives normally it uses less fuel and more on boost. What's the secret ?
:)
Matt Cole
17-10-2008, 22:35
New poster! (less than 10 posts)
Hi All,
I just been reading the May issue of "performance tuner" the Renault 5 featured in the article has had adjusted fuelling on the carb ,so when he drives normally it uses less fuel and more on boost. What's the secret ?
:)
err, no secret mate, when on boost you use more fuel! It may mean a bleed valve which is a waste of money. The carb would have to be reworked for a new max boost ceiling if its more your after and a carefull note of the AFR's will get you a well controlled fuel range.
so where exactly are the stage 1 an 2 enrichments on the carb? :)
the solex 32dis in 30 seconds....
jets of most interest are:
main jet,
air corrector,
1st stage,
2nd stage,
needle valve
think of the main jet as something that changes the mixture at every point, be it driving around town or wide open throttle on-boost. increasing it's size increases fuel everywhere, allowing for more boost but making the off-boost driving rich also, often too rich (standard is 1.2mm, much more than a 1.27mm main in a standard carburettor is excessive)
think of the air corrector as something that helps add fuel on-boost and at higher rpm's. the smaller you make it the richer things will get on-boost at high rpm's (standard is 1.2mm, much smaller than 0.9mm is excessive)
think of the 1st stage as having similar function to the normal enrichment circuit you find on an n/a carburettor. it richens things up when manifold pressure comes close to carb-top pressure. typically you do not want to change this, it works fine in nearly all cases with the standard 1.0mm jet installed.
think of the 2nd stage as being the jet that provides additional fuel only when on boost. logic tells you that this is the 1st jet you should be changing if you're just trying to increase boost a little above standard. (standard is 1mm, any more than 1.4mm is excessive)
main jet is located in the fuel bowl, access via the 12mm nut on the front base of the carb body.
air correcor is located in the top of the emulsion tube, visible when you remove the top half of the carburettor.
1st stage is the jet that looks just like an air corrector jet (and they infact are interchangable) which is located in the triangular-shaped enrichment section that you un-screw (3 screws) from the passenger side of the carburettor.
2nd stage is the non-removable (smart arses need not reply ;) ) brass bush that is located in the carb body, visible once you've removed the enrichment section described above.
as power increases, the order of jetting should be:
increase 2nd stage 1st, max 1.4mm
decrease air corrector next if you still need more fuel, min 0.9mm
increase main jet next if you *still* need more fuel, 1.3mm max.
I won't start spouting what boost levels I think certain jets are suitable for, different engine's in different states of tune vary, buy a wideband kit and measure it properly.
the final jet you sometimes need to consider in higher powered cars is the needle jet. it regulates the rate of fuel entering the carb's float bowl. standard is 1.7mm. sometimes above 180hp or so this becomes too small. increasing to 1.9mm or 2mm help's keep that bowl full, but downsides can be poor running, hesitation between gears, the valve not sealing because fuel pressure is over comming it and poor idle (because of poor valve sealing). It is important to drill very carefully, or buy a bigger jet.
you will know when the float bowl is emptying because AFR's will suddenly go lean, typically in higher gears at higher rpm, say 4th gear at 6000rpm. a gradual leaning would point to a too-large air corrector as mentioned above.
before upping needle jet it is wise to check your fuel pressure at the carburettor, which should be always 4psi above carb-top pressure. If it drops off on-boost then you should be looking at the fuel pump and associated ancillaries first.
excellent info there scoff :agree:
dave j gtt
18-10-2008, 01:09
legend :smokin:
topic with a good clear title, get a real good clear answer :)
That would be my old car in PT, & yes, as Scoff says, i had drilled the 2nd stage out & added a larger needle jet to fuel for 24psi manifold, still on a 120 main with a .9 a/c.
Don't go mad with the 2nd stage drilling, if you only want say 20psi then you may omly need to drill it to 120 or 130.. mine was 140, drill bits can be bought off ebay for a fiver.
Also look in the articles section from the header as there is a thread in there on how to change the jets....
Added your post to the thread as well Scoff ;)
Steve
so will a smaller air corrector only make it richer on boost or will it make it richer off boost as well? :)
Andrew Cooke
18-10-2008, 09:25
so will a smaller air corrector only make it richer on boost or will it make it richer off boost as well? :)
the air corrector is flow, not boost driven, of course it's hard to get flow without boost, so all things are connected.
Excellent write-up there Scoff :agree:
mr bean aka pete
18-10-2008, 11:18
Excellent write-up there Scoff you should put that in the files section :p
It's in the Articles section :rolleyes:
so will a smaller air corrector only make it richer on boost or will it make it richer off boost as well? :)
like andy says, the air corrector comes into play when there is a lot of air flow. you don't have much air flow at low rpm's, off boost, so it doesn't make much difference down there. this is why you'd always want to shut the air corrector down before you started upping main jets (which DOES needlessly richen things up off-boost)
Jamie Eddolls
19-10-2008, 19:44
New poster! (less than 10 posts)
Wow that's what I call an answer - cheers Scoff
Where the heck is the idle screw on my car, am I stupid or something lol its annoying me! someone link me to a pic please
http://img.photobucket.com/albums/v355/FRIX22/SOLEX_51.jpg
idle screw circled for you to see!!
Tiny Tim
20-10-2008, 11:18
Thats the idle jet mate, not the screw.
Tiny Tim
20-10-2008, 11:20
Here you go...
http://img.photobucket.com/albums/v355/FRIX22/SOLEX_51.jpg
idle screw circled for you to see!!
idle screw is bottom left of that picture.
I added some bits to the file section last night that I had saved from the old RTOC site please take a look and add any solex 32 Dis information to it
There is a pic of where the idel screw, mix screw, idle jet are located not scoff's pic But I do remember he did 1 but unfortunatly I couldn't find it so done another
http://www.rtoc.org/files/?path=Technical%20Files/Solex%2032%20Dis%20Carb%20Information/
idle screw is bottom left of that picture.
lol, thats the one!
Thanks guys, i'm sure I was turning that screw before but nothing was happening ?! must be me..i'l check again 2nite
Tiny Tim
20-10-2008, 12:57
Thanks guys, i'm sure I was turning that screw before but nothing was happening ?! must be me..i'l check again 2nite
The idle screw should make a difference when turned. If by turning the mixture screw, you have no noticeable change in running speed/feel/ tone then its possible the tip of the screw has snapped off.. quite common.
Yea nothing happened..screwed it both ways..flat head screw right..il have a look later, im just trying to raise the idle speed by like 200rpm
The idle screw should make a difference when turned. If by turning the mixture screw, you have no noticeable change in running speed/feel/ tone then its possible the tip of the screw has snapped off.. quite common.
do you mean the end of the mixture screw may have snapped ?, as when turning the mixture screw on mine, it was possible to screw it all the way in with the car still running.
Tiny Tim
20-10-2008, 13:32
Yip. Should look like this...
http://cgi.ebay.co.uk/RENAULT-5-GT-TURBO-NEW-CARBURETTOR-MIXTURE-SCREW_W0QQitemZ160249013077QQcmdZViewItem?hash=ite m160249013077&_trkparms=72%3A1301%7C39%3A1%7C66%3A2%7C65%3A12%7C 240%3A1318&_trksid=p3286.c0.m14
the solex 32dis in 30 seconds....
I made that 32 seconds Scoff....
:rolleyes:
Yip. Should look like this...
http://cgi.ebay.co.uk/RENAULT-5-GT-TURBO-NEW-CARBURETTOR-MIXTURE-SCREW_W0QQitemZ160249013077QQcmdZViewItem?hash=ite m160249013077&_trkparms=72%3A1301%7C39%3A1%7C66%3A2%7C65%3A12%7C 240%3A1318&_trksid=p3286.c0.m14
bloody hell, they've gone up, last one I bought was 82p. that was 10 years ago mind :D
is there any easy way of removing the mixture screw from the carb?
no Scoff.....
CGB have gone up, Renault still the same old....LOL
7701034196
how many...???
Tiny Tim
20-10-2008, 14:02
About £3 from Renault iirc???
had 10 last week ...
£0.90 each
Tiny Tim
20-10-2008, 14:08
had 10 last week ...
£0.90 each
Exactly. Its cheaper oop norf... :laugh:
Must just be Bournmuff, pretty sure i paid under a quid for one earlier this year..
Very interesting read ..... just wanted to know can you buy a bigger needle jet (from where) and where its location is in the carb (any pics) ....... cheers.
Anyone ????? Can i buy a larger needle jet from anywhere ???? Or is drilling the only route ....... cheers.
Some carb models fitted to the Peugeot 505 ran a 2mm needle valve, which conveniently also fits the 32dis.
If you can't find one at your local breakers, try Southern Carb's in Wimbledon who should be able to help.
Failing that, time to get ya 2mm drill bit out...
Cheers for that mart , ill try southern carbs before i decide to drill :)
Just tried southern carbs and they are unable to help me out , any other places to try before its drill time ???
Some carb models fitted to the Peugeot 505 ran a 2mm needle valve, which conveniently also fits the 32dis.
..
Drilling the needle jet out to 2mm ain't too bad a job, get yer drill bits out. Going bigger than that is a nightmare to get it to seal though. Im sure Rob@Backyard had got a 2mm needle from somewhere new recently, might be worth dropping him a pm to see where he got it from.
I'm suprised no ones mentioned the old peugot 505 needle jet
:D
there are others, where did rob/BYR say recently he'd purchased some ? maybe they were larger than 2mm though.
Tried southern carbs for the 505 carb needle jet but no luck , anyone know what carb model i should be looking at for 505 ????? cheers.
Rob@Backyardracing
03-11-2008, 19:18
I'm suprised no ones mentioned the old peugot 505 needle jet
:D
there are others, where did rob/BYR say recently he'd purchased some ? maybe they were larger than 2mm though.
Yep we bought the whole lot from a company a while back, dont know why. Maybe to sell on in different sizes up to 2.2;). We havnt had much chance to even give these a proper test, but i must say my clio ran slightly lumpy and part throttle driving.. Was fine on WOT but im still emptying a 2mm. I did have the odd bog now and then but i got **** fuel pressure on idle, well to much... Had a mini reg sat here for months too, i should get this on and try a few out...Lazyyyyyyyyyyyy me:ashamed:
Andrew Cooke
03-11-2008, 19:26
Mart normally goes on about a bigger valve from something else, I'm surprised he hasn't piped up yet, maybe he'll spot this and chip in.
Mart normally goes on about a bigger valve from something else, I'm surprised he hasn't piped up yet, maybe he'll spot this and chip in.
Who?
Only advice I can give is have a look into the Peugeot 505 :)
Everyone's a comedian...
;)
rs250nut
31-12-2008, 13:02
Can some one help me with my carb jetting, Im about to start to bang my head against the wall, I seem to be getting enough fuel at wot but on over run I getting afrs as high as 30.5, this cant be good.
rs250nut
31-12-2008, 13:54
Some one help me :cry:
Tiny Tim
31-12-2008, 13:56
Might help by listing what size jets you're using and boost level
Can some one help me with my carb jetting, Im about to start to bang my head against the wall, I seem to be getting enough fuel at wot but on over run I getting afrs as high as 30.5, this cant be good.
don't worry, it's normal. you won't actually be running at 30:1, an engine won't run at that. on overrun with the throttle closed you max out the idle circuit, it'll go deliberatly lean, there's no point in putting fuel in if the engine isn't being asked to work. a lean AFR on ovverun won't damage anything. :)
rs250nut
31-12-2008, 14:00
Im not 100% sure on a.c or main but I have just drilled the second stage to 1.2. Boost is set at 20psi for the moment
rs250nut
31-12-2008, 14:03
The car does not seem to want to idle now either, do I adjust the idle screw to suit or is there another way I can sort this?
The car does not seem to want to idle now either, do I adjust the idle screw to suit or is there another way I can sort this?
thats a seperate issue then. it might also pop on overrun too then.
likely causes are blocked idle jet (common if you've had the carb apart), missing or poor adjusted idle screw or an air leak below the throttle. :) clean the idle jet 1st, it might foul up a couple of times for the next few miles until the crud you disturbed works it's way out.
rs250nut
31-12-2008, 14:10
Real loud pops and bangs on the over run, its weird because before I drilled the second stage bush it idled sweet at a 950 bang on. I only removed the three screws needed to get at the bush.
Tiny Tim
31-12-2008, 14:12
Real loud pops and bangs on the over run, its weird because before I drilled the second stage bush it idled sweet at a 950 bang on. I only removed the three screws needed to get at the bush.
You'd be amazed how the smallest bits can block up the idle jet. I had to blown mine through so many times when I did my old 11.
as I say, clean the idle jet ;)
when you take the carb apart you disturb tiny particles of crap that otherwise would sit there minding their own business. since the idle jet is only 0.4mm it's the first thing to block and cause those symptoms.
rs250nut
31-12-2008, 14:15
I dont have a compressor in the garage but i do have a can of carb cleaner.
use a single bristle on a wire brush with some carb cleaner, that'll do it.
Tiny Tim
31-12-2008, 14:17
lol your mouth will do mate! Unscrew it, CAREFULLY remove the torpedo and give it a good blow.
rs250nut
31-12-2008, 14:19
On a serious note chaps this has been the best 20 odd nicker I have ever spent, If I were a member of this site back in 2000 when I brought my first five I could have saved myself a whole heap of money.
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