Just serviced the pump, this is the old diaphragm, I do believe it’s seen better days, it’s bowed up about 8mm in the middle and feels brittle, as opposed the the new one which is flat and flexible, unfortunately I’ll have to leave the bike a week to see if it’s made any difference to the “not starting after being left a while issue”.
I have a 1999 M900 and have what sounds like a similar problem for the last couple of years. Starts really easy if it has been running in the last few days. If it hasn’t been running say for a week then it is very hard to start and seems to flood as smell of petrol if using the choke but rarely starts without also. I cleaned the carbs last year but problems remain. I had thoughts that the starter motor was using too much power as when letting off the starter it would sometimes fire. I stripped the motor and replaced the brushes. I thought it was better but problem remains. I have checked the starter circuit and all good. I am wondering again about the carbs and whether I need to replace diaphragm and jets so will be interested as to whether yours is better with new diaphragms. It’s a frustrating problem!
Hi Clive, I’m next starting the bike on Saturday and I’ll post the result on here, I’m a bit dubious as to the fuel pump diaphragm being the fix, the only mechanism I can think of is that the fuel is evaporating in the bowls over the week and the fuel pump is taking time to refill them due to the diaphragm not operating efficiently, seems a bit of a longshot really but we’ll see, sounds like very similar symptoms on your bike, I’ll let you know. PS replacing the fuel pump diaphragm is really easy, but put a mark on both halves of the pump before you strip it, I didn’t and then found that the screw holes aren’t “poke yoke” so it can go back together in the wrong orientation for the inlets/outlets, luckily there was a smear of dirt across the joint that I could line up to get the halves in the correct position
My 900m was often a pig to start after a week or so. It also had running problems once it was going. Carbs all cleaned serviced many times due to the running problems. Failed to cure the problems so out of desperation looked into the fuel pump . Diaphragm was hard and bowed. Replaced the diaphragm and sure enough the running issues were sorted but the poor starting remained. When mine does finally fire up it tends to be on one cylinder then the second one will chime in 30 seconds later. I know the carbs are ok as I’ve been through them so many times.
Nope!, tried to start it today, difficult to start, would like to know what’s causing this, if the bike is started daily it starts immediately, if it’s left 3 or 4 days it’s reluctant to start, very strange
My money is on a vacuum issue (or lack of one). Is it worth checking the diaphragms? There's no logic to it but it's maybe worth a go and they're usually responsible for most running issues on CV carbs. Back in the 90s I had exactly the same scenario on a Yamaha TDM850, which I always put down to the vacuum fuel tap. It turns out the TDM uses exactly the same carbs.. Perhaps it was a bit of both but once running regularly it was perfect. Off the road for around 3-4 weeks waiting for valve shims and it was a complete nightmare to start.
you may be onto something there Travellingman, when I stripped the pump there was surprisingly little fuel in it, I was next going to check the inline filter that I fitted ages ago, but the vacuum petcock or vacuum line to it is definitely worth a look, thanks.
From what you've described it just sounds like you're not drawing enough fuel, so hopefully it's the right track and you can get an improvement..
I’ve bypassed the vacuum petcock and installed a manual one in place of the inline filter that I had fitted, unfortunately I’ve now got to wait at least 3 days before attempting to start it again, if it fires right up then it proves it’s the vacuum petcock (the inline filter wasn’t blocked and the vacuum line to the petcock was fine), so if all goes well I’ll just need to get a new vacuum petcock and put it back to standard.
Ha, true, I’ve been off work for the last 2 weeks and been able to ride every day bar one when it rained, so I went to the national motorcycle museum instead (well worth a visit), tomorrow however it looks as though it’s going to be torrential, oh well I’ve had a good run!.
Neat job there. If it works and let's hope the wait is worthwhile, I'd be inclined to leave it as is. I found the OEM tap on EBay for £19 odd, so good either way.
Success it would appear, not started for 3 or four days, turned the inline tap on, pressed the starter button………. it fired instantly, just like the old days!, I may just leave it on the manual tap, I couldn’t find an OE tap on eBay. So if your Ducati with a vacuum tap begins to get difficult to start it’s worth looking at the tap, thanks to all above for your help. Nipped out to the pub for a celebration Diet Coke
That's a result Mark! Good work there. As regards the OEM tap, I was using 58840051A. There's also 58840071A but I'm not sure what the difference is. The former is on EBay and latter is available from Stein Dinse. I like your manual tap though..
Ah right, it’s this type of tap travelling man, at 83+ I think I’ll stay with the manual version, that said I’ve just realised I’ve forgotten to switch the fuel off, so into the garage I go, doesn’t really matter provided the float valves are ok but you never know!, I might try a generic vacuum petcock, they are around a tenner on eBay
That explains that then! Sorry for the confusion. The old ritual of turning the fuel taps off, which I kind of miss. Pleased you got it sorted..
Ha, yes old school, (and if I wasn’t so old I’d probably have remembered to turn it off!) That’s 4 of my bikes where I need to remember including the James Captain, CB750 & GT250A , I’ll get the hang of it eventually
Thanks for this thread Mark. I will have a go at my tap hopefully in the next week or two. Looking forward to finding a solution!
