Hi All, I posted in the Tech section but I thought I'd try here as well... I have an '95 M900 which came to me with FCR39 carbs. The bike has a manual fuel tap which I forgot to switch to 'off' after a ride, next day I opened the garage to find a pool of fuel on the floor. I pulled the plugs and sure enough the bores were full, cranked her over to pump it out. Drained the oil and the crankcases were also full of fuel, changed the oil and filter. Now the bike won't start. It cranks fine but there isn't the slightest attempt to fire, nothing. Checked for spark and compression & timing, all good. Pulled the fuel line from the pump on the carb side and there is a good flow of fuel. Looking down the carbs when twisting the throttle I can see the fuel squirt as you would expect on FCRs, but after cranking the plugs are dry suggesting no fuel. So how is fuel getting to the carbs but not into the bores? Any words of wisdom before I strip the whole thing down? Very confused!
Right, fixed it. When I checked the fuel pump I only looked at the fuel side, not the vacuum side. I had a brainwave tonight and pulled the vacuum pipe off the pump, cranked it over and sure enough fuel came pumping out. Disconnected the pump-to-carb pipe at the pump end and rigged up a temporary gravity feed, she started right up. I reckon the carbs were entirely innocent in the engine flooding event, the fuel must have gone straight up the vacuum pipe and into the intake. What I don't understand is why there was no rough running before hand, an unlucky coincidence that the fuel pump let go whilst the bike was parked up I suppose? I guess I'll never know. Anyway, I had a spare pump in my parts stash, that's now fitted and normality is restored. I haven't pulled the old pump apart yet but I'll get a rebuild kit on order. Cheers Darren
That is very interesting .. thanks for posting. I've heard of a few cases of FCRs flooding overnight. I also have a pair of 39s awaiting fitment to the monster and I was a bit concerned about encountering the same problem myself. Measures would be taken to try to avoid this, but without understanding the actual cause I would have been working blind and probably would have over-compensated. Things should be a little clearer now. I await a progress report with interest.
Hi Utopia, yes I'd read a lot about FCRs flooding over night too, so when my bike flooded I naturally blamed the carbs. However it looks like in this case the fuel pump let go, my guess is the membrane was already weak and leaving the fuel tap switched to 'on' allowed the pressure to build up to the point where it finally gave up. Fuel then flowed freely up the vacuum hose and straight into the intake, filling up the bore and eventually the crankcase. That's my theory anyway! A good demonstration of how you can convince yourself a problem lies in the wrong place. If I hadn't had access to Google I probably would've worked more methodically and found the problem sooner! Cheers Darren
My M900 has FCR carbs and whilst I've not had a problem with flooding/leaking, I did fit a 12v electric fuel cut-off valve that is wired in conjunction with the (electric) fuel pump so that once ignition is off the fuel is automatically switched off, preventing the crankcase-full-of-fuel scenario that some have suffered.
Yep, I've got a solenoid cut-off on order! No way I'm going through that again. Is your's a later bike with an electric pump as standard or have you retro-fitted one? An electric pump is something I've been thinking about but I understand the FCRs don't like too much fuel pressure. Cheers Darren
My bike is a 'bitsa' but it has a fuel tank from an ie model which has an internal pump & filter. To avoid over-pressurising I have fitted a 'loop' system (as indeed used on ie models) where the fuel is effectively pumped from tank back to tank and then fitted a 'T' (or rather a 'Y') piece connector to the shut-off valve which then outlets to a 'T' to the two carbs. Fuel pump/shut-off are are powered from the ignition module that will prime for a few seconds when switched on and then run continuously when the engine is running in the same way as ie bike. Most of the fuel is just being pumped around the tank with the bike only taking what it needs - I've had no fuel related problems so it works well enough.
Sounds good but I don't really want to fit a plastic tank, I read somewhere that there were some crossover models with a metal tank and an electric pump, maybe that is the route I need to take. Thanks for the info Darren
Mine is a metal tank, from a Monster 'Metallica' which was a range of 900ie models with metallic paint on a steel tank. But I think all the 900 models had steel tanks, maybe even the 1000DS also had a steel tank? Otherwise you could probably fit an external electric pump in place of the vacuum job?
So the problem is still not completely solved... I've just been for a first ride (I haven't had the chance since I replaced the pump) and the bike is really down on power, when on the gas it sounds and feels like is only firing on one. I thought the air filter may be to blame so I pulled it out, no dice. I've also noticed that every now and then the left-hand carb (as I'm sat on the bike) coughs, especially at idle. It's the left-hand intake that provides a vacuum to the pump. I rigged up a temporary gravity fuel feed and the idle seemed to be a lot better (no coughing), but of course I can't ride the bike like that so I have no idea if it solves the poor-power issue. Interestingly if I put my finger over the open end of the vacuum pipe the coughing returns, but if I leave it open to the atmosphere it goes away. Could the vacuum pipe be damaged (split)? I may replace it just to see what happens. Any other ideas what could be causing this? I'm wondering if a full tank would be enough to gravity-feed the carbs so I could bypass the fuel pump and go for a short ride with the vacuum pipe disconnected... Thanks Darren
I'm not sure if this will assist or just confuse the issue but I notice that you replaced the pump with a spare that you already had. I've heard that the diaphragms don't like being left to dry out, so there's a fair likelihood that the second pump isn't on its best performance. Possibly a red herring but worth bearing in mind perhaps ?
I'm not sure if this will assist or just confuse the issue but I notice that you replaced the pump with a spare that you already had. I've heard that the diaphragms don't like being left to dry out, so there's a fair likelihood that the second pump isn't on its best performance. Possibly a red herring but worth bearing in mind perhaps ?
Similar scenario on my 900 Monster (Again with 39mm FCR's). I thought the flooding was due to the petcock being defective? Bypassed this and bike started but not as smooth and the odd backfire? Spark was good but doubted the fuel delivery, moved the vacumm hose to the opposite carb intake (But then snapped the union that goes into the carb intake). Still a working progress
