Running rough

Post by **speedy231278** » Sat Sep 13, 2014 11:48 am

I think I have a fuelling issue on my NC35, but I can't trace it. My conclusion is poor fuel flow, but of course you can conclude anything....

Yesterday, I got stuck in traffic and the bike got extremely hot. It cooled down fine, however when I tried using any decent amount of power, it coughed and spluttered so violently I thought it was about to blow up. Not your usual dull misfire, but a full-on shuddering like it was trying to imitate a pogo stick! Anything over 11K at that point was impossible, and it randomly did the same at much above 6K for a while. After being stopped for an hour or so, it was fine again until I tried to use higher revs, at which point the same scenario kicked in. I took it home and inspected the filler cap, stuffed some wire through the tank breather to check for blockages and also blew through the overflow hose. Nothing seemed untoward. I did manage to get a good hiss out of the filler cap, but only after blowing/sucking on the overflow hose, and only once. I don't see how anything related to the overflow as opposed to the breather could cause a vacuum in use anyway, there's no muppet sucking on the thing when the bike is running....

I took the bike out again, and it was absolutely fine all the time I was ambling around using maybe as much as 8K. Not a care in the world, felt like it always does. As soon as I used over 10K, the same issue reappeared. Violent faltering, and then everything was randomly rubbish over 6/7K. As it was on reserve, I filled it up, hypothesising that maybe if there was a flow issue, the weight of a full tank might help ease things, but the bike coughed and died as I left the forecourt! I opened and closed the filler cap, then it started and I went on my way. Although, I had to fire it up twice because rather randomly it stalled when I put it in gear despite the stand being up and the clutch pulled in. In fact, that was the second time it did that yesterday. Again, it was happy to behave as normal as long as I didn't ask for more than about 8K, otherwise it would go sulky again if it was revved higher.

What should I check next? My thinking is still that it's a fuel supply issue and that high revs are emptying the carbs, which is why it gets sulky at lower revs for a few moments before gradually allowing more to be used again. Fuel tap would be the next port of call I suppose. Does anyone know roughly what sort of rate the tap should flow? It seems to come out OK, but without being able to put a figure on it, it is hard to quantify. For the record, it didn't matter if the fuel was set to main or reserve. Oh, and the tap has been HRCd.

Also, my overactive mind is suspicious about the stalling with the stand up. The light on the dash was very definitely not lit, and the clutch was definitely pulled in, but the clutch position shouldn't matter unless the bike is in gear, should it? I'm just wondering if maybe the excess heat has caused some sort of wiring issue related to the sidestand circuit and it's telling the ignition to kill the spark when the affected wiring gets hot again when using more power and generating more heat? No, that sounds pie in the sky...

richyrd5 · Post by **richyrd5** » Sat Sep 13, 2014 1:03 pm

Ant.could it be that something(inlet rubbers.ignition!)has roasted/expanded and thats what is causing problems.suppose its a case of trial and error checking stuff...good luck!!.oh btw.no can do on the tyre yet chap!!!.hopefully next week if you still have it!!cheers.

Post by **speedy231278** » Sat Sep 13, 2014 1:15 pm

Erm, I think you're maybe thinking of the other speedy?

richyrd5 · Post by **richyrd5** » Sat Sep 13, 2014 1:48 pm

Lol.oh dear..yes your right.just ignore the tyre bit!!

Post by **dobbslc** » Sat Sep 13, 2014 4:53 pm

Have you checked the coils? Such a violent on and off stuttering sounds electrical to me.
One of the coils might be failing under load at higher rpm as it draws more current.
Also test the battery voltage on idle and at high revs to see it it's getting a charge.
It could also be one of the safety cut outs ie clutch or stand switch playing up try bridging or opening the wires to the switches, some are "normally open and some normally closed" so you will have to try both ways to see what let's the bike run.

Post by **speedy231278** » Sun Sep 14, 2014 4:43 pm

I do have spare coils. I did have reason to test one of the current ones a while ago and it was in spec, but didn't have any reason to test the other one. The bike has got that hot before without any issues so I'm a bit mystified. One other reason for thinking it was fuel is that I forgot to turn the fuel on when I left Goodwood the first time, and the bike ran out without even a hint that it was going to. Usually, it'll miss for a few hundred yards before stalling, but on that occasion it was like it was just switched off. I was just about to give up and phone the RAC when I realised the fuel was off and I couldn't remember if I'd turned it off when I came to grief or hadn't turned it on... lol

Post by **speedy231278** » Wed Oct 01, 2014 5:31 pm

Fitted a secondhand sidestand switch today. The pins on both side of the connector were bright blue when I unplugged the existing one, so I reckon it wasn't making very good contact. Gave the loom side of the thing a very good clean, as well as the 'new' one although it was pretty clean. Have done plenty of miles at high revs which were previously a no go area and so far so good. I suspect merely cleaning the contacts would have sufficed rather than replacement, but I didn't really want to be taking the thing apart again to get at the connectors a second time!

Running rough

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