ive mentioned this on here in the past , never really got to the bottom of it and tried to manage but probably worth resurrecting the issue in the hope someone might know the answer.. 1600 standard engine throughout , runs very well normally , until I fill it up I’d say over half full - it won’t tick over very easily, cuts out on the approach to junctions and is hard to restart ( smells very rich / Petrol) once on the open road it’s fine with an occasional hiccup , almost like it’s cutting out but then is ok again, seems to worse coming out of a sharp bend or roundabout . Once the fuel level drops it’s fine - no problems at all. Like I say I can manage it by not overfilling it. It’s had a new tank and I don’t think there’s anything in the tank that’s being disturbed when the fuel level is high as I would have thought it would be like it regardless of levels. I had a theory that maybe the extra pressure of the fuel on the pump or float valve in the carb is flooding it somehow ?? Any theories guys ???
Unlikely to be tank. Any modest increase it pressure wouldn’t make it past the pump, I’d think. As above, I’d start with the carb.
I read something a while back about shims - can’t remember seeing any instructions - is it in the Bentley ? Do you think it sounds likely to be this?
I’ve just checked and it does refer to it in Bentley and gives the measurement , I think I’ll try a slightly thicker washer
I don’t get any fuel leaking past it whilst sat on the drive , nothing in the oil which I thought was a result of a poor sealing valve ?
I’m only theorising, but are the tank breather pipes doing their job. If they have got partially blocked, air wouldnt be able to get in to replace fuel going out. The effect would be more noticeable with a full tank. You might be able to test this by blowing down the breather pipes. Maybe.
Carburettor float valve being overwhelmed by extra pressure from the tank added to an internally leaking knackered petrol pump: The pump is working just well enough to lift petrol from the bottom of the tank (its only got to produce a bit over 0.25 PSI to get fuel up). Then when the tank is full the extra 0.25PSI from the head of petrol in the tank just pushes the level in the float chamber up a fraction and into the overflow ...
The 0.25 is imperically correct, and doesn't seem much in the scheme of things, but is if your on the high pressure end of things. Worth knowing the pressure your pumping, a fuel pressure guage or T piece and a vertical clear pipe going vertical about 4 meters ' upstairs bedroom window is useful. Aiming for 3 psi I think, cut a piece if steel shim for under the pump if required.
May have found the culprit this evening - blew down the breather from the air filter with the filler cap off - petrol spewed out of the filler ( brimmed it) seemingly ok Blew down the breather that goes to the carb - blocked solid , found a kink in a joint pipe - sorted that and all clear now . So fingers crossed that may be the issue - can’t get my head round these breathers though , so a pipe from the carb goes up to one of the expansion bubbles and the tank , the one from the air filter doing the same the other side - how does it work - wizardary ???
The breathers usually meet in a T piece in the middle then both go to the air cleaner. Each side loops up through the bulb in the air vents then down to the tank and crosses over to a vent on the opposite side of the tank . So no matter which way the bus leans there is an air feed to the top of the tank. And the bulb stops neat petrol getting up over the top of the loop in the air intake. And the air cleaner connection means there is a light vacuum pulling fumes back in. If a breather is connected to the carb body then a monkey has assembled your bus. What could be happening is that the vacuum from the carb is just sucking petrol up the misconnected breather pipe and into the carb...
I think your pipes are wrong. Breathers from the tank on both sides go to a t-piece and then to the air cleaner. Anything from the carb, if you’ve got a stock Solex, will have a vacuum on it, and may go to either the distributor or the hot air actuator on the airbox. You may be sucking air out of the tank. Put them in the right places and see if things improve.
Right I think we might be getting somewhere.. It runs barely... not good, worse than before which is good in a way... Like I say I brimmed the tank the other day , by mistake really because I wasn’t sure how much was in there. The left hand side breather ( the one that was kinked ) was connected directly to the carb, I’m guessing that before the pipe was unkinked that the carb was sucking against it with little issue - when the tank was fuller or when going round a bend I’m guessing a little fuel got sucked passed the kink and into the carb causing the problems I was having.. Now the pipe is unkinked and the tank is full - fuel is being sucked directly into the carb ( pulling the pipe off the carb proves this as fuel Comes out) So as you guys have pointed out the breather shouldn’t go to the carb as this photo Once I take this off and put the Tee piece in I reckon we should be good, I can’t try it tonight as I took the carb top off and ruined the gasket .. So the breather tees together and goes to the air filter.. I’m ok with that , the pipe from the carb goes to the hot air actuator - I’m ok with that. At the moment there is a pipe from the actuator which goes into the back of the air filter - not sure you’ll see this from this photo So what which pipe should go to the back of the air filter?? Disclaimer - none of this has been done by me - it’s always been like it Sent from my iPhone using Tapatalk
Was it connected to the side port of the carb? That should be connected to the vacuum can on the distributor. There should be a short length of pipe on the air filter that connects the thermo-switch on top to the round flap actuator on the air filter snout. There should be another vacuum connection that is piped to the second connector on the thermo switch. This vacuum either comes from a small pipe on the side of the inlet manifold bdlow the carb, or from a rear port on the carb (which you don’t appear to have).
Showing my limited mech knowledge here, but if the vac advance is connected to a breather rather than the manifold, wouldn’t the bus run like a dog on a light throttle? Or am I misunderstanding something?
Can’t really see from the pics what’s connected to what. If the vac advance on the dissy was connected to something weird, it just wouldn’t contribute anything. You’d have mech advance only, shich would work fine, apart from sudden throttle inputs.
