Running badly at low rpm.

[blade023]

Hi all, wondering if anyone can shed some light on an issue i'm having. Last night on the way home from work the bike (gen1 fzs1000 ) started ok, but part way into the journey it started losing power at low revs and stuttering really badly like it was struggling. I've always been used to having plenty of power even as low as 2k but now anything below about 3-4k and it's stuttering quite badly. I'm going to check what I know how to, i.e; spark plugs, exup and airbox but if anyone has any input on what else to check I'd appreciate it. Will post an update with more info when I get a chance, but it looks like the 1 day off I have will be spent fettling.

Cheers.

[b1k3rdude]

If its just instantly started happening on that day on the way home then its unlikely(but not unheard of) to be the plugs/coils.

• Does the bike sit for while in-between journeys..? You might havea tiny bit of water in the bottom of the float bowls. There is a screw at the bottom of each bowl, just drain each bowl for a 1-2 second and then nip the screw backup etc.
• Check the fuel filter isnt clogged.
• Check the breather pipe isn't kinked (have you been working on the bike recently?) - if the pipe is kinked it can cause a momentary air lock in the tank stopping fuel from flowing.
• Check the fuel pump is working correctly, (check the electrical connector and fuel hoses)- if the bike is make a clicking nose when you first try to start it after its been sat for a while then the pump is fine.
• You say stuttering, is it that or just a lack of power? Lack of power might be down to the exup valve seizing.

[Falcon 269]

Check plugs and plug leads/caps first.  Unscrew the plug caps, trim 1/2" off the plug lead and screw it back into the cap.

Poor slow running is often symptomatic of partially blocked pilot jets but if you are using the bike regularly, this shouldn't be a factor.

[b1k3rdude]

Check plugs and plug leads/caps first.  Unscrew the plug caps, trim 1/2" off the plug lead and screw it back into the cap.

How would plugs and caps start failing all of a sudden if they had been previously fine..?

[PieEater]

I think the ends of the HT leads can get brittle with heat and age and then engine vibes can then loosen them off so they don't make as good contact with the plug cap connector. I keep meaning to do mine.

[blade023]

Thanks bikerdude, that gives me a starting point for tonight. I'll do some late night fettling in the hopes of saving my day off.

[unfazed]

I think the ends of the HT leads can get brittle with heat and age and then engine vibes can then loosen them off so they don't make as good contact with the plug cap connector. I keep meaning to do mine.

Close to the mark Pie eater, but what happens is that the end of the leads soften due to heat and lose shape, the wire in the lead can corrode due to water ingress and the connection goes high resistance killing the spark and yes the engine vise cause them to loosen off. Reason I know is that I spent part of the day sorting the original plug caps of a 600.
Stripped and cleaned the connection inside them including the small washer which can break in half and spring ends. Broke open a few old NGK ones I had hanging around and used the resistors from them as they are better than the originals and do not require the small washers (NGK are 5K Ohm and seem to vary by 5% whereas the OEM are 10K Ohm, but vary by 20%. I trimmed 10mm of the end of the lead and cut open the trimmed bit, the wire was corroded but the lead was out of shape and softer than the rest of the lead.
I was messing with the old screws from the NGK caps I broke and they were quite loose in the pieces I had cut off
Bike running sweetly now at all revs

Unlikely to be water as it would effect starting more than running, but will do no harm to drain the carbs anyway just to be on the safe side, might be dirt in there
 

[b1k3rdude]

I think the ends of the HT leads can get brittle with heat and age and then engine vibes can then loosen them off so they don't make as good contact with the plug cap connector.

They would have to be pretty loose to cause such sever poor running and at a specific rpm. And surley this is limted to high mileage/age bikes though?

[unfazed]

 

I think the ends of the HT leads can get brittle with heat and age and then engine vibes can then loosen them off so they don't make as good contact with the plug cap connector.

They would have to be pretty loose to cause such sever poor running and at a specific rpm. And surley this is limted to high mileage/age bikes though?

Not necessarily as the bike I was fixing was a 2003 with only10000 miles on it.

[old son]

My bike runs fine when its dry but sometime in the rain it holds back as though the spark is not getting through. Maybe I need to trim back some of the HT lead?

[unfazed]

Had a similar problem with the 600 and what I did was trim the leads, roll back the rubber boot screw in the lead, coat the boot area and where the lead enters the cap with vaseline. roll the boot back on and never had an issues since.
On the 1000 I did a similar thing after trimming the lead, coat the lead near the end with vaseline and screw it back end. A messy job but worth it. Make sure the drain holes are clear.
 

[silverfz]

Could it also be inlet rubbers perished a
bit?

[b1k3rdude]

Could it also be inlet rubbers perished a bit?

I cant see them cracking over night though..

[Falcon 269]

Although I've seen hundreds of the intake stubs with surface cracking, I know of only a handful worldwide that have actually developed leaks. 

[unfazed]

Although I've seen hundreds of the intake stubs with surface cracking, I know of only a handful worldwide that have actually developed leaks. 

+1 same here

[blackcabbie]

i had similar probs .... did all the sparkplug stuff..... made no difference..... my scottoiler vacume connector to the inlet stub was cracked letting in air...... check all your vacume guage  connector stub caps are sound.

[b1k3rdude]

• i had similar probs .... did all the sparkplug stuff..... made no difference.....
• my scottoiler vacume connector to the inlet stub was cracked letting in air...... check all your vacume guage  connector stub caps are sound.

• It never is most of the time.
• Doh, never thought to ask the OP to check his vacuum stubs!

[positron]

I know we haven't heard back from OP (blade023), but I experienced something similar yesterday morning on way to work. Massive stuttering up to 3.5-4k and plenty of power after that. This lasted most of my way to work (70 kilometers). It was less obvious on the way back and no sign of any issue this morning. In my case I suspect it's my own doing - the night before, I replaced the coolant and sticking a garden hose down the radiator cap meant water went everywhere. Or perhaps running the engine with tank tilted (so that I can access the radiator cap) might have dislodged some crap from the bottom of the engine into the fuel line. In either case it seems to have sorted itself out this morning. 

[unfazed]

Water in the plug caps is the most likely issue from what you were doing. Once it dried out it was fine.

[blade023]

Sorry for the delayed reply guys, and thanks for all the input. I checked the chain, tightened and lubed it as it needed doing, and since then the issue has all but gone. I suspect there's still something I need to check out there, but my next task is to go over the exup and make sure that's good. While i'm at it i'll check a few other bits mentioned here. Just don't have much time spare between doing 70+ hours/week.

By the way, I hadn't done anything to the bike before this happened, and there hadn't been any rain either. It's in a locked shed at night, left for 10-12 hours between each 30min commute, hence the confusion about the cause.

[hotmetal]

I doubt it's the exup cos if that sticks then you'll get the 7k-0-RPM indication on the tacho.

One thing that has been known to cause similar problems is if something is restricting the air intake. This can be something as silly as an Autocom lead or bit of rag too close to the intake under the seat/tank area. Probably a long shot but as it takes 1 minute to check then worth a look! Hope that helps.

[blade023]

Ah yes, very true hotmetal, I 'd forgotten about that. In that case I'll check the air intake when I next get the chance. Strangely it's running absolutely fine now, though I know there are a couple of things I need to go over still.

Cheers guys.