I think I've mentioned this on another thread somewhere but can't find it... Anyway, for a couple of years now I've suffered with rough running every now and again, from an annoying every now and again blip when running at speed down to actually cutting out at junctions and generally having trouble driving in traffic through towns etc.. At one point I was convinced it was electrical as it seemed as if the ignition was very briefly switched off , similar to flicking the ignition key off for a split second, so I've changed all my ignition components and the problem still persists. I've had the carb off and cleaned it thou roughly more than once, new fuel lines and filter recently ( more of a safety reason than fault finding) but I think o have narrowed the fault to mainly occur straight after fill ups , particularly to the brim. This morning I did a 30 mile trip home and filled up ready for a 90 mile trip in the morning...the camper was barely driveable for the one mile from the filling station to home, cutting out on the driveway with a very strong smell and fuel and almost not starting again. I know I shouldn't brim it when filling but with a very iffy fuel gauge I find it hard to work out how much I should be putting in. I had a new tank and rubbers fitted a couple of years back so would like to think thats not the problem,Someone mentioned it could be a breather issue and they are getting blocked which does seem likely but even after 20 or 30 miles of a fill up it still plays up, surely a blocked breather would be clear after a few miles ? Any pointers on what to look for would be most appreciated
When you say brim it, do you meen to the nozzle clunking off or right to the top so you can see it. you may be over filling and pumping fuel into the breather system aswell which it may not like.. possibly overfill going straight into carb from the breather loop. Check for leaks at your breathers....
Probably not with a new tank... but crud getting churned up from the bottom of the tank and then causing intermittant blockage? Or condensation forming water at the bottom under the fuel?
You might just be suffering from fuel over pressure overwhelming the needle valve in the carb. if this happens especially after a blast as you back off the excess fuel dribbling makes it go very rich and stumble or even die. Then another symptom is it gets hard to start. And some of the fuel ends up in the oil too.. This is a problem with new fuel pumps. When I eventually get my bus back from its MOT fail the first thing I will be checking is the pressure. A progressive like mine is even more vulnerable than stock carbs to over pressure as its a Weber.
The symptoms you describe there are exactly what seems to happen Mike, my fuel pump hasn't been replaced ( I did buy one thinking it may be the culprit) what would be the solution do you think? New needle valve ?
I've just had a quick once over, I pulled the breather off the carb and fuel dribbled out I blew down the pipe and it seemed to be free flowing , the breather to the air filter was as dry as a bone, so it may seem as @mikedjames says every now and again neat fuel getting being dripped into the carb causing an over rich mixture causing a 'cough ' at speed and cutting out at low speed. If this is the reason for the rough running is there a way to stop it other than not over filling ? Some sort of pea trap prior to the carb perhaps?
Its worth a try. I believe the 34 PICT-3 service kits come with a new needle valve ( a brass thingy with a hex nut on it) that you can bolt into the top cover of the carburettor float chamber. As you get the problem while you are going along and it stumbles a bit it seems likely - the too rich condition makes idle a bit tricky too, I have been stuck after dropping off someone about a mile into a drive while the choke was still on and it dribbled. A shutoff solenoid will help the other more damaging dribble while the engine is stopped with a full tank and the tank just dribbles through the leaky valve into the manifold and fills up the sump with petrol. In the end this can trash your engine big time as petrol is nothing like as good at lubricating bearings. On my instruments it showed the Air Fuel Ratio going very low when it drips following by a sudden flicker high as the fuel stops burning and you get all the oxygen coming out as nothing is burning in the engine
I did buy a rebuild kit a while back but can't remember if I changed the needle valve or not...I'll check the bits I have left over and see.
Drove the 90 miles to the Norfolk coast today for a weeks RnR ..drove like a sack of pap for the first 30 miles or so then not too bad after that ..so looks like its overfilling being the problem..
Popped £20 for the return journey and she ran mostly as sweet as a nut, only faltering accelerating out of a roundabout or sharp bend . So it does seem to be something to do with fuel level, now I know can work round it but would like to know what's causing it ...I'll change the float vale as suggested by mike above as a starter
When your changing the valve - measure the fuel level in the bowl - 19.5-20.5 fo 68-70 17-19mm for 71 12 -14mm for dual carb Bentley suggests using different washers to adjust, I bent the tab on the float bowl that sits on the needle.....
If your gonna open it up,replace the needle and the seat,don`t just change one. Spend a lot of time checking your float too. Firstly before you go crazy with anything , check your float level before you disturb anything then you may get an idea on what is happening. When you get the float out give it a good shake next to your lug hole and listen for anything in there, test the float by submerging it in petrol with a weight on it to keep it all under the level of fuel in a bowl for a good hour or more, overnight is even better, then give it another shake. also when you put it back together, spend a bit of time checking the float level, too much and you`ll have probs just like this, too little and it might starve. When it`s being naughty have you whipped the plugs out quickly , or even pop the leads off and find where it is firing and where it isn`t firing. Ozziedog,,,,,,,,,,,,Naughty naughty busses
Oh yeah , might be a good idea to fix the fuel guage properly. There are just so many mods on the vent systems over the years and I don`t think they got it perfect on the aircooleds. If you didn`t have to get it all up the filler neck itd be a bit better ,you may be submerging parts of the venting system and choking it. Ozziedog,,,,,,,,,,,,,,, its only a sender and a guage innit ??
Its on the list to try and sort it out, I don't like too much guess work , I'll try the guage first, wish I'd changed the sender when the tank was renewed...schoolboy error
