Zoidburg Posted January 30, 2011 Report Posted January 30, 2011 Hi all, My KE-30 coupe has been flooding whilst the engine is turned off, caused by evaporating fuel in the tank building up too much pressure. This suggests my charcoal canister unit needs replacing. I fitted a fuel pressure regulator which has solved the flooding problem, but now the motor is starved of fuel on the highway and needs more psi than the regulator will allow. Rather than buy another FPR, I intend to remove it and run a return line from the fuel pump to the tank. The charcoal canister has a fuel line from the tank connected to it, but (from what I've read) is designed to emit fuel vapour from the tank to the canister. Would it be possible to use this fuel line as a return line from the fuel pump to the tank? It would essentially be doing the reverse of what it's designed to do, and I'm not sure of the risk involved. If anyone has tried this before or can shed some light on the subject, please let me know as I don't want to blow myself up! Thanks Quote
Trev Posted January 30, 2011 Report Posted January 30, 2011 Check to see if the fuel shut off valve on the carby is working, believe that this is why they were fitted. Quote
altezzaclub Posted January 30, 2011 Report Posted January 30, 2011 My KE-30 coupe has been flooding whilst the engine is turned off, caused by evaporating fuel in the tank building up too much pressure That's probably between the pump and the carb I think, so Trev suggestion is the right one. That shutoff solenoid will hold the line from pump to carb under pressure until you turn the key on again. The fuel tank should be connected directly to the charcoal canister so fuel pressure can't build up in the tank. My SUs do the same on a hot day when I park. You can smell fuel evaporating out of them and the solution is actually to fit overflow return lines back to somewhere like the charcoal canister. Maybe when it annoys me enough... Quote
Zoidburg Posted January 30, 2011 Author Report Posted January 30, 2011 Okay, no conclusive answers there. I'm running factory twin carbs on a 5K in my KE-30 coupe. I just had the carbs rebuilt and the line from the pump to the carbs holds plenty of pressure after the motor is turned off, too much in fact. I just need to know if it's possible to use the line from the charcoal canister as a fuel return line. Perhaps I should just try a higher rated fuel pressure regulator, and be done with it? Cheers Quote
Trev Posted January 30, 2011 Report Posted January 30, 2011 Okay, no conclusive answers there. I'm running factory twin carbs on a 5K in my KE-30 coupe. I just had the carbs rebuilt and the line from the pump to the carbs holds plenty of pressure after the motor is turned off, too much in fact. I just need to know if it's possible to use the line from the charcoal canister as a fuel return line. Perhaps I should just try a higher rated fuel pressure regulator, and be done with it? Cheers This is why it pays to give all information. What fuel pump are you running? Quote
Andy43 Posted January 31, 2011 Report Posted January 31, 2011 Sounds like needle and seat has some crap in it, or float is set to high Quote
altezzaclub Posted January 31, 2011 Report Posted January 31, 2011 Definitive answer.... No! How will the fuel tank vent both as pressure rises when it warms up in the sun and when pressure drops as you remove fuel from it?? How will you ensure that fuel goes into the carbs at enough pressure to run the motor at peak power and not have all the fuel run off back to the tank via the charcoal line?? When you say "a higher rated fuel pressure regulator", what do you mean?? One that delivers fuel at a higher pressure? I run my twin SUs at 1.5psi & my $50 regulator can go up to 5psi max. If your regulator lets fuel past at 2psi say, then that's all that should be in the line when you turn the motor off. Then the underbonnet temperatures start to soar as all the heat in the block comes out. The petrol trapped between your regulator and the carb needles & seats expands, and it can only push the needles down and flood into the carb to release that pressure. The fuel before the pump should be going back to the tank as it expands, and the fuel between the pump and the regulator should be trapped until the regulator gets below 2psi. The ideal solution is a cut-off solenoid on the fuel inlet to each carb, so it locks the petrol in the line and lets the pressure go up over 2psi until you start it. If not, a return line from the carb side of the regulator leading back to the tank side of the pump. So two "T" pieces, some fuel line and a plug with a needle-sized hole in the line. You want a very small flow back to the tank side, certanly less than 1mm. Quote
ke70dave Posted January 31, 2011 Report Posted January 31, 2011 also make sure you havent crossed your fuel lines somewhere. if you have your breather pipe submerged (ie your return) then when the fuel tank pressurises it will force fuel up your return line and that will flood your carby (i think) i had this happen when i fist hooked up my 4age, but instead of it flooding my carby, it leaked out my dodgy hose connection and spilt fuel EVERYWHERE in my garage from just a few hours of sitting. Quote
Zoidburg Posted January 31, 2011 Author Report Posted January 31, 2011 Hmm, now I'm getting worried! My regulator ranges from .5 to 5.5 psi. When I first fitted the regulator I set it to 3 psi, started the motor and after about 5 mins it began to die and then stalled. I then set it to 4 psi, did the same thing, would not even idle. I then set it to 5.5 psi (max) and it seemed fine, until I hit the highway and the motor started to splutter after 5 mins or so. Driving in 60 km/h zones it's fine, but can't sustain on the highway. For whatever reason, there's loads too much pressure in my lines and I'm only running a Goss mechanical fuel pump. I know this should not be the case, but it is. I just had both carbies fully re-built and pressure tested, so the carbies are not to blame (according to Sprints anyway). I'm beginning to think my charcoal box line is blocked up, and is not venting the pressure out the tank. However, fitting the regulator has stopped the car from flooding after it's been turned off, so I'll try the higher rated regulator for now and see what happens. Thanks for the advice on the charcoal box line, I'll try and figure out a way to check if it's blocked? Quote
Evan G Posted January 31, 2011 Report Posted January 31, 2011 open the fuel cap and see how much pressure comes out then go for a drive? Quote
Andy43 Posted February 1, 2011 Report Posted February 1, 2011 (edited) Hot Idle compensator valve ? Have you had a look to see where the fuel is flooding. We run a one way breather valve on the speedway car, The fuel system does presusise a lot, on a hot day the filler will blow you hand off, But we never have flooding problems. Edited February 1, 2011 by Andy43 Quote
Zoidburg Posted February 1, 2011 Author Report Posted February 1, 2011 Just waisted money on another regulator, the problem still persists... If I move the fuel cap to one side HEAPS of pressure blows out the cap. After reading my trusty Gregory's book, it seems this pressure is let out via the charcoal canister. For starters I don't even have mine hooked up, and the canister itself is probably blocked. Tonight I'll try and test the canister and hook it all up, then see what happens. Can you buy these charcoal canisters new? Thanks Quote
Evan G Posted February 1, 2011 Report Posted February 1, 2011 you don't have it hooked up but you think its blocked?????????????? :blinks: Quote
altezzaclub Posted February 1, 2011 Report Posted February 1, 2011 (edited) Check out the charcoal line back to the tank. If that is blocked then pressure building up in the tank will push fuel through the pump and into the carbs. Just take off the gas cap, pull off the tank line at the canister and blow into it. A mate with his ear at the tank will hear the air coming through. Hopefully that is the problem and it has an easy solution, rather than muck about with regulators. If you can blow through it leave it disconnected and go for a drive, then check for flooding. Edited February 1, 2011 by altezzaclub Quote
Zoidburg Posted February 2, 2011 Author Report Posted February 2, 2011 Re-connected the charcoal canister, and it seems to have stopped flooding. However the front carby is still leaking petrol, I think a gasket on it or something else may be stuffed? Quote
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