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+--- Thread: Rough running in low rpm's (/showthread.php?tid=56108)
Rough running in low rpm's - Mads - 07-10-11
I got this ´98 model fzs600 that I bought a couple of months ago. It has been crashed and is not very pretty but basically runs fine. The idle is i bit rough though. It surges maybe 2-300 rpm up and down. Also when riding in slow traffic in 1st and 2nd gear the bike "jumps" a bit. It's really annoying as my daily commute is in heavy traffic.
I have done a bit of work to solve the problem, but no luck. I have tried the following:
Changed plugs to NGK iridium
Changed the plug caps to NGK
Changed the air filter element
Cleaned the carbs
Synced the carbs
Adjusted the throttle sensor
After changing the exhaust to a set of Motad downpipes and Viper end can I also tried to richen the idle mixture by turning the mixture screws out a few turns.
All of this has had no effect on the problem. Also the problem have been the same with original and aftermarket exhaust.
Whats the next move???
When cleaning the carbs I also checked the camchain adjuster. It's on its final notch and I have a rattling sound especially when the engine is cold, so I need a new camchain. Can I exchange it without taking of the top. And what about the camchain guides?
Thanks,
Mads
(Excuse my English language, I'm from Denmark)
Re: Rough running in low rpm's - His Dudeness - 08-10-11
what sort of condition are you carburettor intake rubbers in? an air leak in them could cause a rough idle like you described. what mileage has the bike got?
Re: Rough running in low rpm's - Mads - 08-10-11
The rubbers seem to be fine. I checked them over when i cleaned the carbs. The bike hos done 65.000 km (40.000 miles).
/Mads
Re: Rough running in low rpm's - His Dudeness - 08-10-11
it might be valve clearances issue. i think tight valve clearances can cause a lumpy idle. at 40,000 they might be out of spec. turning the mixture screw a few turns is probably not a great idea. i think they are fairly sensitive to adjustment. you should be trying 1/4 or 1/2 turn adjustments not a few turns. it might be worth going back to the factory setting and trying again. have you check your plugs since adjusting the carbs? they should be a brownish colour around the electrode
Re: Rough running in low rpm's - Gnasher - 09-10-11
Sounds like worn neddle valve jets/seats to me or oring/s on the seats.
Re: Rough running in low rpm's - Mads - 09-10-11
I guess I will try to adjust the mixture screws back and syncronize the carbs once more. The first time was before I cleaned them.
If this doesn't help I think I will change the camchain, adjust the valves and go through the carbs once more and check for wear. But this will have to wait till the snow comes.
Thanks for all your input.
/Mads
Re: Rough running in low rpm's - Gnasher - 10-10-11
(09-10-11, 10:08 PM)Mads link Wrote:If this doesn't help I think I will change the camchain, adjust the valves
Are you serious cam chains/valves will not cause hunting without further problems of very poor/noisy running unless there are other issues you've not mentioned? Just check the needle jets and/or the rest of the carbs for damage and wear
Re: Rough running in low rpm's - Mads - 10-10-11
Ok, it sounds as if you know what your talking about. I have made many bikes run a lot better by cleaning and adjusting alone. I have never had to analyse wear on carbs other than obvious defects so i really don't know what to look for.
In my eyes the carbs looked fine so how do I tell if the needle jets are worn? How about the o-rings on the seats? Maybe I should just change these to be safe?
Maybe you could give me a few pointers before I rip them apart once more.
I really appreciate you guys taking the time to help me.
/Mads
Re: Rough running in low rpm's - Mads - 11-10-11
Ok, so I did a bit of googling and found this: http://www.factorypro.com/tech/needle_jet_wear.html
That explains what to look for concerning wear in the needle jets pretty well. All the explanations of the symptoms match what I am seeing on my bike. So now I can't wait to tear into it again.
Do you know what I am looking at concerning the price of the needle jets? Should I also change the needles? Maybe it's worth considering a kit containing these parts - if that exists. Does it?
Any other parts I should consider changing when I'm in there? (besides the needle jet o-rings)
/Mads
Re: Rough running in low rpm's - Gnasher - 11-10-11
No idea what the cost is but if any part is worn you need to change BOTH, if one carb has worn jets just change all of them.
Re: Rough running in low rpm's - Mads - 11-10-11
What you are saying is, if the needle jet is worn, change the needle as well and if the needle is worn, change the needle jet? Basicly if ANY needle or needle jet is worn - change the lot?
/Mads
Re: Rough running in low rpm's - Gnasher - 11-10-11
Yep
Re: Rough running in low rpm's - His Dudeness - 11-10-11
i thought valve clearance being out of spec would be a contributer to a lumpy idle? if im wrong i stand corrected apologise for that bum steer.