Reinhoud Posted February 8 Posted February 8 (edited) Gents, My bike has some weird issues lately. After say 15km the bike start running like crap, when I keep going it just slowly dies. Turn it of for about 30 seconds, and off it goes again like nothing happened. Symptoms of an empty tank. Checked the fuel supply, that's all good. Later I thought, because of the way it dies, it might be the ignition, changed over the CDI unit, that's not it. So, today I thought I'll check the fuel pressure. Something went wrong with tapping the NPT thread apparently, so the gauge is leaking a little bit, that means the reading isn't very accurate.. Looks like the pressure is about 0.5psi. It used to be 1 psi. With 2 psi the needles in the floatbowls started leaking. There's enough pressure in the up-pipe that the bike doesn't run when the pitot tubes aren't connected... Even on idle. Not sure if this is important. My question; what happens when the fuel pressure is low? Could it cause the problems I have? Can't get another gauge today unfortunally.. Do the Malpassi regulators need re-adjusting occaisonally? Other question, how long should it hold pressure after the ignition is turned off? Not that that really matters I think, but it shows there's a leak somewhere if the pressure drops Thanks Edited February 8 by Reinhoud Quote
clivegto Posted February 8 Posted February 8 I'm running 1.5psi, could be a kink in a fuel pipe. Quote
Paulm Posted February 8 Posted February 8 Mines running 2psi,as Clive says check for kinks in any pipes and make sure the fuel is definitely returning to the tank,in my experience of Malpassi fuel regs,you don't need to check the fuel pressure unless you're having issues. Quote
badger Posted February 8 Posted February 8 Fuel pump blocked? I've got an in tank pump, the little sock filter pre pump had got a load of crap in between the 2 membranes. Gave these symptoms but I know most people don't use an in tank pump so could be the pump or a blocked filter if you have one? Quote
Reinhoud Posted Saturday at 07:10 AM Author Posted Saturday at 07:10 AM Thanks guys. First time it happened I thought it was the fuel filter. Deleted that after I noticed the fuel tap has got a filter, same problems. Fuel pump seems to be working alright, I pumped 10 liters into jerry cans without problems.. Quote
TLRS Posted Saturday at 01:14 PM Posted Saturday at 01:14 PM Anything changed around the time this problem started to occur? 1 Quote
TLRS Posted Saturday at 01:22 PM Posted Saturday at 01:22 PM Any chance boost makes it’s way into the fuel delivery? Probably won’t empty the float bowls but maybe pushes into the fuel line and changes the flow to the bowls. Quote
Reinhoud Posted Monday at 07:44 AM Author Posted Monday at 07:44 AM On 2/16/2025 at 12:14 AM, TLRS said: Anything changed around the time this problem started to occur? No, don't think so... First it did it occaisonally, sometimes it did it, sometimes I could ride it for 100km and nothing happened. But lately it happens quicker, first around 50km, then around 40km, lately around 25km.. 1 Quote
Reinhoud Posted Monday at 07:49 AM Author Posted Monday at 07:49 AM On 2/16/2025 at 12:22 AM, TLRS said: Any chance boost makes it’s way into the fuel delivery? Probably won’t empty the float bowls but maybe pushes into the fuel line and changes the flow to the bowls. It needs pressure in the floatbowls. When I disconnect the hoses from breather floatbowl to pitot tube, it dies straight away.. It gets progressivly worse. I can feel it coming up, first a littlle bit, and when I keep going it's getting worse. Then leave it for a while, and she goes again like nothing happened... Looks like a clogged filter. Deleted the fuel filter, it has one in the tap, same problem. When I check everything, everything looks fine. I can pump 10 liters into jerrycans with the fuel pump, and nothing weird happens.. Quote
TLRS Posted Monday at 09:49 AM Posted Monday at 09:49 AM 1 hour ago, Reinhoud said: It needs pressure in the floatbowls. When I disconnect the hoses from breather floatbowl to pitot tube, it dies straight away.. It gets progressivly worse. I can feel it coming up, first a littlle bit, and when I keep going it's getting worse. Then leave it for a while, and she goes again like nothing happened... Looks like a clogged filter. Deleted the fuel filter, it has one in the tap, same problem. When I check everything, everything looks fine. I can pump 10 liters into jerrycans with the fuel pump, and nothing weird happens.. Makes sense to have pressure in the floatbowls on a boosted engine. Is your fuel tank pressurized though.. could float valves leak boost? Quote
peter1127 Posted Monday at 09:51 AM Posted Monday at 09:51 AM (edited) check for kinked or ruptured fuel/vacuum/boost hoses. Sometimes hard to find. Or ruptured membrane in the malpassi. Could also be clogged fuel tank vent, that gives this symptoms too. Edited Monday at 09:53 AM by peter1127 Quote
Gixer1460 Posted Monday at 09:51 AM Posted Monday at 09:51 AM 1 hour ago, Reinhoud said: When I disconnect the hoses from breather floatbowl to pitot tube, it dies straight away.. It gets progressivly worse. I can feel it coming up, first a littlle bit, and when I keep going it's getting worse. Then leave it for a while, and she goes again like nothing happened... First line - that shouldn't happen! Even if the pitot was open, the engine should idle - badly, but it should idle as there is no significant boost at idle. Second line - sounds electrical with those symptoms - something heating up to a failure point - cools down and it works again. Quote
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