Carburettor Mixture issue

[ch33kster]

Hi,

I am having issues with mixture on my rebuilt Weber 32 ADF.

The engine fires up but will randomly flutter between 12 and 15,000 revs with the choke being fully open. The throttle isn't open and the timing seems to be close enough to spot on.

When I've adjusted the mixture (inwards and outwards) there is no change at all until the mixture screw is fully removed then the engine stalls.

All the correct ports on the carb are blocked off tight for my 1969 1438cc engine as per a prev. post on here.

I was wondering wether the issue could be caused by the primary jet being too large on the carb. My original DHSA carb had a 45 primary jet where the ADF has a 50. Does the jet size matter depending on the engine size?

Also could there be a vacum leak that's causing the erratic behaviour?

I recently changed the carb to manual choke. Could one of the diaphragms not being operated now?

Dazed and confused.

Thanks,

Charles

[bradartigue]

Sounds like an air leak. Wavering is almost always an air leak. Spray some carb cleaner around the base of the carb and around the manifold and see if the revs jump up or stabilize, that will be the source of the leak.

[maytag]

I think that you should sell me whatever motor you've got that is fluttering between 12 and 15,000 RPMs!!

[baltobernie]

This is not your model, but generally applicable to tuning Webers. The important thing is to know that the "mixture" screw does not perform the same function as on other carbs. Generally speaking, if the "mixture" screw has no effect, you are above the progression holes (idle screw too far in), and are running on the main circuit. In this state, you will see fuel dribbling in from above, even at "idle".

http://www.redlineweber.com/html/Tech/c ... _best_.htm

[majicwrench]

Most all of these Webers have some sort of idle/low speed jet which is very prone to plugging. Even after carb OH. Which is often why the idle mix screw has no effect. Although like baltobernie pointed out, at 1200-1500rpm you may be above the idle circuit.
Can you drop the idle with the idle speed screw?? Does is smooth out with choke partially closed??
Watch spraying carb cleaner around. The flanges on the intake and the carb mounting are pretty trouble free, but the carb will suck in the fumes from the carb cleaner anyway, smoothing the idle and fooling yoiu into thinking they have failed. Also, spraying carb cleaner around is excellent way to start a fire. Any vacuum leak large enough to cause a running issue will be loud enough to hear, grab a couple feet of vacuum hose, stick one end in your ear, and listen around the gaskets, much safer, much more precise.
Keith

[ch33kster]

Thanks everyone.

I tried spraying carb cleaner to find out where the problem was and in numerous areas the ether was sucked in but unsure where from as you say majicwrench the overall test with carb cleaner is very random and less precise. The carb does pull in the ether from the surrounding area so engine note does change.

I have a possible feeling that the inlet gasket maybe at fault. The removal of the inlet manifold is such a pain to get off on the AS Spider as well with the disi cap, fuel pump and the blasted breather housing in the block getting in the way.

The "vacum tube to ear" sounds like a master plan, I'll just make sure theres nothing blocking my ear from hearing right

[sptcoupe]

When you can screw a mixture screw in and out with no effect, it is almost always a pluged idle jet..

[ch33kster]

OK, checked the head and the manifold for any signs of warping, all ok.

Replaced the manifold gasket and sealed it. Checked all gaskets / spacers on the carb and all seem to
be ok with no leaks.

Cleaned all jets and ports and swapped the primary jet to a larger size which seems to have made a slight
difference.

Checked the brake booster hose which is the only pipe connected to the manifiold.

Engine timed. Had the engine running at normal temperature with choke off and no throttle.

Engine randomly rev's up and down between 10,000 / 18,000 now. The mixture screw has no effect unless
its fully removed.

On adding throttle the car seems to accelerate ok without stalling but seems to rev high and then calm down
when the throttle is released.



One thing I have noticed is that fuel is being jetted in through the delivery valve and in via accelerator jet that is over the primary throat.

Bradley Artigues excellent "Engine Maintenance + Modification", page 37, says that
"the accelerator pump may be leaking into the main barrel during idle operation".

This seems to be the case and I have a feeling that the ball valve is sticking allowing the fuel to flow through.
Could this be the case?





I have sprayed carb cleaner / lock free in and around the calibrated orifice and used a fine wine to see if it would
free it up.

I was unsure on wether to drill in above the calibrated orrifice through the brassed cap on the rim of the carb.
The only thing that is stopping me is damaging the "calibrated" element.

Frustrated as ever, especially when we are having a record heat wave summer here in the UK!

Cheers, Charles

[baltobernie]

One thing I have noticed is that fuel is being jetted in through the delivery valve and in via accelerator jet that is over the primary throat.

This is what I'm referring to in my earlier post. Place a piece of paper between the idle speed screw point and actuating lever. Mark the screw when the paper drags. One-half turn in from there. If it won't idle, you need a bigger idle jet.

ps Clamp off the brake booster hose, just in case you've got a small vacuum leak there.
Also check and adjust float level, if necessary, to factory spec

EDIT ONE HALF TURN IN (NOT OUT)

[So Cal Mark]

that doesn't look like a rebuilt carb to me

[ch33kster]

that doesn't look like a rebuilt carb to me

Sorry Mark, what do you mean? Is there something that I'm missing?

[majicwrench]

The tiny jet that plugs in behind that brass screw in your last picture. If you have not, you need to remove that screw and the jet should come out with it. Jet has a TINY hole that is very prone to pluggin. There is likely one on opposite side of carb too.

And again, what happens if you turn the idle speed screw down??

You said you "sealed" the intake gasket. If you used typical silicone sealer, it is gasoline soluble, which mean it will degrade in any carb/intake application. The intake gasket really needs no sealer of any kind.
Keith

[bradartigue]

DO NOT USE WIRE TO CLEAN A CARBURETOR

Never, never, never, never, never, never use wire in a calibrated orifice (which is just about everything on a Weber). Use carb cleaner and high pressure air.

I have to agree with an earlier comment, if you paid $$ for that carb to be rebuilt or bought it rebuilt then it wasn't, the carb is pretty dirty. Since you have the base disassembled you can really clean the heck out of it, just use soft materials and lots of air/carb cleaner.

[ch33kster]

The tiny jet that plugs in behind that brass screw in your last picture. If you have not, you need to remove that screw and the jet should come out with it. Jet has a TINY hole that is very prone to pluggin.

Removed the jets, checked and cleaned again. They are clear of any muck or debris.

what happens if you turn the idle speed screw down??

The butterfly gradually opens up with no issues.

You said you "sealed" the intake gasket. If you used typical silicone sealer, it is gasoline soluble, which mean it will degrade in any carb/intake application. The intake gasket really needs no sealer of any kind.

The gasket sealer has no been removed and the surfaces have been cleaned.

It does seem to be holding a steady rev now but on giving some throttle and then letting off the engine seems to go wild and hold on the revs for a while and then finally calms downs again, this is without the choke on.

Checked the butterflies to make sure that they were seated in the throats correctly and are ok not letting any carb cleaner through on testing. The springs are all ok on the throttle linkage and close back to the correct closed position, this of course is without the throttle adjustment. The spindle seems straight.

The randomness of the throttle is very bizarre and confusing, it seems to be all or nothing. I can feel that Ive conquered the issue and stand back and then all of a sudden the engine will start revving.
Its like bloody HERBIE. I'm getting to the point of drop kicking it.

How much is it approximately to rebuild a 32 ADF? Is it cheaper to buy a new one or should I go for a 34??

[scarlson]

Fuel should not be coming out of the accelerator jet unless the throttle is being opened. There is no pressure differential between the float bowl and the accelerator jet during operation until the throttle is opened, then the diaphragm closes the ball check and forces fuel out the jet. If the jet squirts when the throttle is opened, I'd suspect that everything is working fine.

Are you sure that the float level is set right? The wrong float level can cause all kinds of issues. Too low will prevent the main circuit from being activated at the proper air velocity and will create a lean condition off idle. Too high and it could dribble fuel out the aux venturi during idle causing a irregular idle.