Had further thoughts re re-routing fuel lines and to be honest, I just wonder.......? When I bought the bus it had a single 32/36 Progressive carb on it and it was controlled by a fuel regulator set at 3psi I believe. After not too long I decided to change the carb to twin Weber 40 IDF's but still kept the regulator at the 3, and later 2.5psi. Those carbs never ran really well and I put it down to being old and decrepit (a bit like me really!!) Anyway because those carbs didn't run very well I bought a new set and ............................................. had similar problems. The above tells the recent story. But tonight I started thinking (for a change) and, having tried most things to get the new carbs to run smoothly it suddenly struck me that the way I had the fuel lines set up might be the cause of the problem. Main fuel line goes to regulator and then onto right hand carb and, through the banjo to the left hand carb. I didn't alter the regulator at the time and didn't feel the need to do so. Is this starting to ring any bells yet? The regulator, set at 2.5 or 3 psi will only deliver a certain amount fuel per minute (or whatever time unit you wish to choose) and that volume (and pressure) would be quite adequate for 1 Weber carb. However is it sufficient for two Weber carbs, each requiring 3.5psi (or the volume of fuel that this pressure supplies) especially when the second carb is fed via the first i.e. they are 'in series' as electricians would say. If there are any SACD's out there (see below) or perhaps any mathematicians, can one of you please tell me what my fuel pressure regulator should be set at in order to run two carbs at 3.5psi, but in parallel rather than in series? Do I really need two pressure regulators, one for each carb? Could this be the answer to my long-standing problem? Answers on a postcard please to the following address. Or am I just being a bit silly here?? By the way for those of you who don't know SACD is an acronym ( I bet you guessed that!) for Smart Ass Clever Dicky! Depending on quick responses I shall be adjusting my fuel lines and regulator tomorrow morning
Have you had a pressure gauge inline to see what pressure your actually running? Like paul says theres no series or parralel when it comes to pressure
OK but I just wondered because when I tried to test my regulator it was quite apparent that the higher the setting the more fuel came through in a given time. If there is no relationship between pressure and volume of fuel then why does volume increase with pressure?
It only alows whatever pressure you set to the carbs. The carbs take whatever they need, lowering the pressure and the regulator lets some more through up to the set pressure ad infinitum. So the pressure remains constant and the flow changes with driving conditions. The only way more fuel can come through at higher settings when it's all connected up, is if it's forced past the float valve and through the jets - over-fuelling.
Thanks Zed - I think I get it now, but I'm not sure! Seem to have heard that somewhere else - must be a famous quote
OK - just for fun (!!!) I re-routed my fuel lines and re-positioned the regulator and things seem to be getting better in as much as there is some adjustment on all mix screws now - a step in the right direction but I'm not sure why re-routing fuel lines would help unless there was a partial blockage or the pump had problems pumping uphill. I shall try some fine tuning tomorrow and see where we get. I've had enough for one day!!
Have you tested the fuel pressure at the pipe just before it enters each carb? I think you'd have to ensure the float needle is shut on the opposite carb to get an accurate reading.
Thanks for the thought but I think I'm sorted now. Must admit I've always just accepted that the pressure regulator is fairly accurate but recent tests and performance seem to confirm that's true. Haven't got the means to measure pressure anyway but if I had it would be interesting just to confirm that pressure is stable throughout the system.
