Massive over-fuelling problem!! :0( someone please help

[HULK]

Right peeps, always knew my car was overfuelling badly it didnt used to be too bad but its gradually got worse.

I suffer from the following

1, poor fuel comsumption
2, badly sooted plugs
3,car bogs down under load
4, engine gives off a massive back fire when i turn the engine off


Hooked up a wideband today and the afr readings were shocking

normal driving is around 12.8- 13.5

WOT is 10.6- 11.5!!

would leaning off the mixture screw make any difference??
what things would cause the carb to over fuel as bad as this.

I havent looked at what size jets are in the carb yet, previous owner just told me the carbs set for standard boost but looking at the afr reading it must have a massive main jet in there surely


really really confused

[James5]

you need to open the carb up and with a micro drill set see what size the main jet is along with the 2nd stage jet and the a/c jet

Right peeps, always knew my car was overfuelling badly it didnt used to be too bad but its gradually got worse.

I suffer from the following

1, poor fuel comsumption
2, badly sooted plugs
3,car bogs down under load
4, engine gives off a massive back fire when i turn the engine off


Hooked up a wideband today and the afr readings were shocking

normal driving is around 12.8- 13.5

WOT is 10.6- 11.5!!

would leaning off the mixture screw make any difference??
what things would cause the carb to over fuel as bad as this.

I havent looked at what size jets are in the carb yet, previous owner just told me the carbs set for standard boost but looking at the afr reading it must have a massive main jet in there surely


really really confused

[Kris M]

mixture screw only alters the mixture at idle, not under load

[Brigsy]

turn the boost up

[J$£5GTT]

turn the boost up

[HULK]

I will check what size jets is in there for sure.

what makes the carb flood?? will the carb overfuel if any of the jets block up??

[Jimmy_GTT]

I will check what size jets is in there for sure.

what makes the carb flood?? will the carb overfuel if any of the jets block up??

Maybe the air corrector.
But I think your main jet is not the std size.

[HULK]

turn the boost up

On a serious note, would turning up the boost slightly make it a bit leaner right across the rev range???????????

[James5]

On a serious note, would turning up the boost slightly make it a bit leaner right across the rev range???????????

Yeah it should do

10.6-11.5 is quiet a wide range you want to aim for a max afr @wot of about 12.1

you really do need to find out what size jets are in your carb as I said above.

[Spooky]

See I think 12.1 is bordering on a little rich...I've aimed for 12.5 and averaged 12.3 afrs upto 6.5krpm @ 20psi at w.o.t in 4th/5th...

Strip the carb...

Fit a standard main jet...1.2mm...maybe reduce the a/c to 1.1/1/0.9mm...

You will need to modify the 2nd stage enrichment...open it out to 1.3mm...

Use the wideband with every change you make and log it.

Always good to start from standard if possible

[HULK]

I have taken the top of the carb off. The a/c jet is the standard 125 I cleaned it and I cleaned the emulsion tube also. Put it back together and it is now idling at a afr of 9.5 what the hell. :0(

[Markey Mark (BD)]

Pull the main jet out and measure that plus measure the 2nd stage jet, see what they are.

[James5]

Pull the main jet out and measure that plus measure the 2nd stage jet, see what they are.

As I said above on my first post

[Maka]

have you checked the main jet??
bet its 130 - 150mm range as they are readily available aftermarket quick remedies to putting boost up.

you need to have a look at your vent size as well.

if its wider than 25mm someone may have put the bigger jet in to stop it running way to lean.

but like most have said, check the main jet size, then check your secondary enrichment. i believe its 1mm as standard.
they do get drilled out up to a max of 1.4mm to help with WOT.

if the carb is filling up and brimming then maybe also check the needle jet hasnt been drilled. standard is 1.7mm. these sometimes get drilled out to 2mm and have sealing issues.
can be larger than 2mm which will have issues sealing alot of the time.

i have a 120 main, 25mm vent, 2mm needle, bolloxed up air corrector and 1.4mm 2nd enrichement and i pull just under 12s (to low 12s depending on charge temp) at 20 psi on a T28 and piper 285.
nice and strong.

[Maka]

On a serious note, would turning up the boost slightly make it a bit leaner right across the rev range???????????

depends.
you could have a standard needle jet and enrichment jet. and just a big silly main jet.
which i believe if you up the boost woud be ok until you hit 4th and 5th gears and high rev ranges. where the float chamber may empty and then you will run very lean as you will run out of fuel.

also you could have a larger vent (so called group A mod) which at higher boosts would run mega Lean (16 afrs etc!) with a large main jet but standard secondary enrichements.

[HULK]

Thanks Maka!!

How do I measure the venturi and how are vents on carbs made larger are they ported out??

[James5]

Thanks Maka!!

How do I measure the venturi and how are vents on carbs made larger are they ported out??

Vents = Venturi and these are normally machined out to the size required I have seen a couple of 28 but these are the biggest I have seen in a Solex 32 Dis.

Measuing the Venturi is fairly difficult as you need to disassemble the carb to measure the i.d. of the venturi. An easy way to visually see if the venutri is a different size is that the standard venturi has 25 stamped on it and normally if they have been enlarged or changed the 25 stamp is normally 1/2 machined off.

See the following pics

1st pic is standard venturi
https://www.rtoc.org/files/Technical%...n/IMG_2942.JPG


The 2nd pic is an enlarged Venturi carb.
https://www.rtoc.org/files/Technical%...uri%20carb.JPG

[rs250nut]

Vents = Venturi and these are normally machined out to the size required I have seen a couple of 28 but these are the biggest I have seen in a Solex 32 Dis.

Measuing the Venturi is fairly difficult as you need to disassemble the carb to measure the i.d. of the venturi. An easy way to visually see if the venutri is a different size is that the standard venturi has 25 stamped on it and normally if they have been enlarged or changed the 25 stamp is normally 1/2 machined off.

See the following pics

1st pic is standard venturi
https://www.rtoc.org/files/Technical%...n/IMG_2942.JPG


The 2nd pic is an enlarged Venturi carb.
https://www.rtoc.org/files/Technical%...uri%20carb.JPG

You can measure them roughley with deep sockets, find a socket that fits then measure the o.d of it

[HULK]

Thanks chaps. 25 is still present inside so it hasn't been touched

[Brigsy]

If you get stuck mate pop down here, should be able to sort it

[Spooky]

If you get stuck mate pop down here, should be able to sort it

Good shout

I'd offer but I'm fcuking miles away LOL!

[Maka]

i still had 25 stamped o nthe side of mine when i first brought my road sl*t!

take the carb top off and drop a socket in the top or very crudly, open a compass in the venturi and then measure it against a ruler!

[HULK]

Thanks for all the help lads. Thanks for the offer Brigsy, Would it be safe driving to yours with afrs of 10.0 all the way across the rev range???

[Brigsy]

I imagine it would be alright just chucking black soot out/drinking fuel. Im going to york raceway sunday/monday could pop by?

[HULK]

Right peeps problem is now solved.

For everyones information the carb had standard jets all through out the carb, still now don't understand why it was running so so rich.

Anyway all I have done is take the carb off the car and take the top off. Removed all the jet and emulsion pipe thing and cleaned them all out with carb cleaner. Cleaned the carb inside and out also gave the outside of the carb a polish with my dremel, I have change the mixture screw for a new one although the old one looked fine.

Another thing I did was set the accelerator pump arm with the 5mm drill bit trick. Before I couldn't get a 3mm bit between the throttle plate and venturi so I'm wondering if this was the cause??

Anyway afrs across the board are now perfect so I'm now over the moon.

Big thanks to everyone who has helped on this thread and via pm. Really appreciate it!!

Really don't know how I would manage without this website.

[Spooky]

After reading your first post, the accelerator pump arm probably sounds like the culprit.

Glad it's all sorted

[jesus in the seat of a 5]

, good darts , told you it was standard...., glad your now happy.