Wet carbs... ctn'd...

yes I do... but I do like the way they sound and the way it cleans up the engine bay :-) I never pushed the car hard when i had the stock air boxes so can't tell for sure...

What I want to see is if I can corner hard with the lower pressure / softer spring and maybe find the right balance for long distance runs.

The problem I used to have is the kind that 99% of V12 E drivers will not have as it would take something like 300 or 400 miles of sustained high speed cruising for the fuel starvation to happen... The way I drive the car is slightly out of the norm :-)

Pascal Gademer
72 E-type 2+2
00 XKRCoupe
99 XJR

Pascal- do you remember the exchance we had on the air filters (and ballance system inside the filter housing) we had some time ago. I am sure that the problems you are having are pressure problems (as you know) and that you can not solve it because you have a variable--under bonnet heat. That is always a problem down south with those BS add on filters- they sound good and look great anf were available when Jagusr built these cars but the variables were too great and performance was unpredictable. A pressure gauge will do you no good as the max reading should be only 3 psi and I have never seen an sutomotive quality dial that would read this accurately or a scale small enough that interperlation was not a problem. Did you have this problem prior to removing the stock system?
George Camp

another hour and and a half of testing... This time I lowered the pressure by reducing the return valve spring strength and driving till everything got really warm,etc...

I have the pressure set a bit too low so the car loose power after a while when it gets hot ( just like it used to before I increased pressure last may)

Origninally, when it wasn't very hot ( 20 miles / 30 minutes), I was able to make it stumble on hard left accelerating turns... however when it got real hot, I wasn't able to make it happen... After 90 minutes of stop and go, cruising and trying to find places to accelerate hard into 2nd gear while turning... there was no evidence of fuel leaking out. Filters were dry.

of course the problem isn't solved because low pressure means after while, I loose power while cruising... when that used to happen, it sometimes would take a few undred miles before the heat would reduce the pressure to the point of starving the left bank.

I'm going to try to increase pressure by adding little washers behind the spring... one at a time... and try to find a fuel pressure gauge I can mount in a hidden spot for troubleshooting purposes...

Pascal Gademer
72 E-type 2+2
00 XKRCoupe
99 XJR

Well, I experiment with pressure tonight... inconslcusive so far. I first lower the pressure to much, compressed the spring and was able to blow thru the retrun valve quite easily. Immediate Fuel Starvation as soon as it was warmed and I tried to sustained 50mph...

increased it up a bit gradually, to the point where I could sustain hard accelerations ( on a failry long and steep causeway bridge, 1/3mile up to 80 or 90 ) without stavation. Now of course, the same problem happens on hard cornering.

Now what I'm going to try next is lower the pressure after it's hot and see if it cures the leakage...

I'm also going to install a fuel pressure gauge and use little washer to adjust the valve. I tried with a nut but it compresses to much...

interesting how much of a difference that spring makes...

btw, how is the fuel system on the 6cyl ? is there a return line with such a valve?

PAscal

Pascal Gademer
72 E-type 2+2
00 XKRCoupe
99 XJR

Pascal,

Good to hear this is making sense to you, but I'm totally confused; what kind of BMW is that anyway?

Seriously, I'm glad you showed the picture. What is the other hole/passage at 9:45 for? Is subject hole (the one at 10:00) the same diameter/position on the rear carb as it is on the front carb, only the front has a brass insert? I can't tell if the diameters are the same from your picture and this is becoming more and more important. Is the diameter of the insert constant or does it neck/taper down? The carb I have is not from a S3 and is slighlty different; mine does not have the second hole at 9:45. The fact that gas is coming out of the inserted hole is, IMHO, only a symptom. I would not block it with sponge rubber because if it drops back down into the bowl your going to have trouble. BTW subject hole has nothing to do with the choke. If my assumptions are right, my solution would consist of fabricating a metal baffle to prevent the gas from sloshing around in the bowl, much like baffles are used in the oil sump to prevent the oil pump from cavitating during hard cornering. This would help keep the gas level more constant at the needle's jet which is really the important issue here. The plumbers who first designed this type of carb never thought guys like you would be trying to brake Art's slalum record with their invention.

Stew Cleave
JOCO Chief Judge
'69 E-Type 2+2
and other LBC's

Now it's stating to make sense.

seems that simple solution would be to route that vent higher up so that any gas would flow back down and/or having a little bit of foam there to soak up the excess gas. a small hose inserted in the hole might just do the trick.

I just remembered I had a picture taken when the car was rebuilt with the carbs exposed, it's in the Gallery but here is a crop of the higher res.

Now, I immediately notice that the rear carb doens't have that hole so that hole must have something to do with the choke on the front right carb.

Pascal Gademer
72 E-type 2+2
00 XKRCoupe
99 XJR

Pascal,

The oval hole relieves pressure from the space between the piston and the diaphram. It lets the pressure balance so the diaphram can move freely. Keep in mind pressure can be negative or positive. Negative pressure is sometimes called suction but sometimes it helps to think of suction as negative pressure. Now the other hole; this passage goes directly into the float chamber or bowl. The carb I have in my hand does not have any brass insert and the passage is rather large and unrestricted; the smallest cross section being at the face. Outward centrifical force, caused by a left hand turn, would send gas up this passage and into the filters, but the brass fitting (oriface) should restrict this somewhat. The purpose of this passage is also to relieve pressure, in this case it lets the air escape from the float chamber as gas flows in, otherwise you'd be compressing the air - not good. Now, what do I think? Sorry, I need to know more about the brass fitting you say is pressed into the face of this passage; what size oriface (hole) is it and is the oriface the same size on the other carbs? Be forwarned, your ultimate solution may be fuel injection.
Stew Cleave
JOCO Chief Judge
'69 E-Type 2+2
and other LBC's

Thks Stew !

Great desctiption that helps understand.

The hole I was refrering to is on the vertical surface where the air filter is bolted. looking horizontally from the ouside, there is an oval shaped hole at the 12 oclock position and that rond hole with a metal insert at the 10 oclock spot. that one is the one leaking some fuel.

btw, what's the top oval hole for ?

I'm goingt o to try lowering the pressur tonight, easy to do...

Pascal Gademer
72 E-type 2+2
00 XKRCoupe
99 XJR

Pascal;
I went out to the shed and got a carb body out of my stash - just to make sure I'm describing things right. I have it in my hand. I will assume you are looking straight down after removing the dash pots and diaphragm. So here we go; on the left side of the carb (looking at the engine from the right hand side) there is a small hole slightly below the center of the bore that runs from front to back - the throttle is at the engine end of this bore. This choke hole is at about 10 o'clock from the jet which is centered straight down. Of course if your looking straight down you can't see this hole, you have to move back away from the engine to see it. This hole is angled back at forty five degrees. I just stuck a Q tip in it to determine the angle, and yes I stuck it in from the choke side with the choke assembly removed (I have a bare body with no insert). Gas sucks up from the bowl through the assembly and into the bore. As George Camp said, you probably have too much presure; or the choke assembly is dirty, worn, or both and won't seal shut. My S2 manual describes the operation of the choke. Remember, the English add gas to choke, Americans cut off the air (and maybe add gas by depressing the pedal which activates a plunger that squirts gas into the bore). This is why you never depress the gas peddle when choking a LBC. Good Luck.

Stew Cleave
JOCO Chief Judge
'69 E-Type 2+2
and other LBC's

I guess can try lowering the pressure are the return valve... does't hurt to try !

but were is that hole going to too ? the one at about 10 oclock on the face of the carb? anything to do with the choke ?

Pascal Gademer
72 E-type 2+2
00 XKRCoupe
99 XJR

Pascal. Three words- pressure, pressure, pressure. The choke gets its fuel from the same bowl.
George Camp

there are kits around to fit SU, which are indeed supposed to be easier and give a bit morepower... but my four ZS are other wise working fine and were rebuilt a couple of years ago.

I'm wondering if that's somehting others V12 E might be suffering from. it's tough too troubleshoot as under normal driving conidtion, even spirited, it just doesn't happen... only when the car is pushed to the limit...

Does the choke have a vent hole like that ? how does it work any way ?

Pascal Gademer
72 E-type 2+2
00 XKRCoupe
99 XJR

Pascal,

Go to bed it must be 11:00 PM back east.

Speaking of time, 10 o'clock would be on the choke side of the carbs? Have you dismantled the choke assemblies and cleaned them. Mine had gunk all over them and maybe, if your's have gunk, the gunk won't let them seal. Be carefull, you can reassemble the bloody things backwards which is a cheap way to run around rich.

Will SU's fit? SU's are so much nicer.

Stew Cleave
JOCO Chief Judge
'69 E-Type 2+2
and other LBC's