so I have this modified Cagiva Elefant, fitted with an ST2 944ie motor. The fuel pump is external (inlike the in-tank item on an ST2) and I have problems with the bike stumbling and running really bad on part throttle and cruising after filling up the tank. Any ideas? Wrong pressure (there is a regulator in the fuel return line)? Breather problems? The Cagiva tank, of course, was designed for an air cool 900cc with carburettors, so trying to understand what’s wrong with this setup. Thanks nG
Hard to say without seeing the set up. The ST pump and regulator are both in the tank, your's presumably are both outside it. How does the return from the regulator get back to the tank?
Ok so here’s my setup (I didn’t make it, bought it like that) - Cagiva tank has 3 outlets, all bottom 2 left 1 right - Rear left one and right connect to a T piece that goes to the fuel pump - fuel pump to injectors rail - other end of injectors rail goes to left front tank port, I’ve been told the regulator is in that return line, haven’t checked it for myself yet. - tank has whatever breather it came with (assumption) Can post pics if that helps. Thanks!
It seems like the fuel pressure is being affected by the head of fuel in the tank. Apart from the pump location the setup should be similar the 907ie. The pump outlet should pass through a filter then to the injectors. The pressure regulator comes after the injectors with it's outlet returning excess fuel to the tank. To prevent sediment from the tank from entering the pump you should also have pre-pump filter.
Thanks Derek. I’m thinking the pressure from the 24L of fuel in the tank is disturbing the return flow, in turn disturbing the fuel flow in the injector rail. Gonna take it apart and see if I can add a long tube to the return port, going up inside the tank to its top so return fuel flows into top of tank - so can’t get affected by the amount of fuel it’s holding at any time.
So i’ve done it and it’s helped a lot! Finally the bike runs right no matter how fuel is in the tank. I added a 500mm long copper pipe to the fuel return port, which inserts straight up into the tank so the return now squirts very near the top, eliminating the pressure of 24L of fuel against the return line, and it’s done wonders. No more stumbling/misfiring/surging at part throttle and cruising, it’s pretty much smooth all the way now. Result!
Well I spoke too fast.. 130km into the current tankful and not only it started stumbling again mostly around 3000rpm on slightly open throttle / cruising, it now completely conks out at random intervals! Seems to happen more when idling, although a couple of times it happened while running, just seems to lose spark or fuel or something - just goes dead. While running it came back each time within a second or two, but when dying at idle, it then wouldn’t start again for a while, then suddenly go normally again. Fuel or electric gremlin? Any suggestions or insights welcome.
All fuel hoses are fairly new and leak free. The air box connects directly to the inlets - are there any other air hoses I should be aware of?
Think I finally found it! The culprit was the 4 prong connector from the ST2 loom that has the four wires to the combined fuel pump and level sensor, located to the left of the battery on my Elefant. The top two connectors that feed the fuel pump are slightly burnt out, and made a bad earth connection to the pump. Tomorrow I will attempt to clean and lubricate properly, if it happens again that connector will have to get replaced. That was a bit of a headache, glad I found it in the end and hopefully it’s all good again!
Ended up cutting the wires and soldering them together as the connector was shot. But, it still runs like shit at 5-10% throttle. Stumbling, surging, generally not happy. It’s ok on idle, and as soon as I twist the throttle a bit more, say 25% and up, it’s absolutely fine. Just impossible to cruise smoothly. So annoying!
You have reminded me, does your bike have a fuse box on the dashboard to the right of your dials? I can’t remember if any of the fuses will affect constant running but the contacts aren’t quite up to the job and can also run hot/melt.
