Lumpy at low revs (<4000 rpm), fine above

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jimsym
Posts: 93
Joined: Sun Feb 03, 2013 11:39 pm
My Bike: ZXR 400 L9
Location: Hertfordshire

Lumpy at low revs (<4000 rpm), fine above

Post by jimsym »

Hi guys,

Ive recently purchased a 13k mileage 1999 ZXR, which has been looked after reasonably well, but hasnt got a full breakdown of what it has and hasnt had serviced on it over the years.

It sounds and runs very well above 4000 rpm, but any revs below that (including idle) cause it to run very lumpy if that makes sense?
It does however start on the button every time if that makes a difference.

For someone who is very limited on space, and quite hesitant to 'tinker', is there anything I can try that might fix it before I pass it over to a professional?
zimm
zxr400 oc member
zxr400 oc member
Posts: 2320
Joined: Tue Oct 10, 2006 12:32 am
My Bike: ZXR400-M4, ZX4, ZX6R.
Location: Herefordshire

Re: Lumpy at low revs (<4000 rpm), fine above

Post by zimm »

check the pilot jets are clear and mixture screws are set correctly then get the carbs balanced.

dont know where you are located but happy to help if you're anywhere near me.
GibboN
Posts: 57
Joined: Tue Nov 20, 2012 11:57 am
My Bike: ZXR400 M4 ('94)
Location: Hong Kong

Re: Lumpy at low revs (<4000 rpm), fine above

Post by GibboN »

I got out on my bike for the first proper run last night and had a very similar experience.

Bike starts on the button (except for hot starting but understand this is a common issue) but if I pull away with anything less than 4,000 revs the bike will judder a little or even stop dead. By the end of the journey I was pulling away with 5-6,000 revs each time.
Occasionally switching from first to second gear resulted in no acceleration (double checked I wasn't in neutral each time this happened) and then the bike would cough and splutter to a stop. I'm putting this down to my gear changing rather than the bike at the moment though.


It just feels like the bike wants to be ragged. If I try and run it quietly/low revs it doesn't want to know if you get my drift. Is this something to be concerned about?
I just picked it up from the dealership last night so it's had some good quality love and attention. Worth going back and checking again do you think? :smt009
ross46
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Posts: 825
Joined: Fri Aug 26, 2011 9:31 pm
My Bike: zxr 400 l6

Re: Lumpy at low revs (<4000 rpm), fine above

Post by ross46 »

know this is a little out of date now but the little 400s dont have that much torque anyway and our ones have all the power at the top. you can get it to run smoothly under 4k but it still wont like pulling away at that low revs
jimsym
Posts: 93
Joined: Sun Feb 03, 2013 11:39 pm
My Bike: ZXR 400 L9
Location: Hertfordshire

Re: Lumpy at low revs (<4000 rpm), fine above

Post by jimsym »

Woah blast from the past.

Since that post, I've thoroughly cleaned the carbs, reset the idle and pilot, balanced the carbs, and it now runs very well across the whole rev band- even at low revs it has a very linear power delivery so no problems there.
Erika
Posts: 5
Joined: Mon Sep 30, 2013 7:39 pm
My Bike: zxr 400
Location: north wales

Re: Lumpy at low revs (<4000 rpm), fine above

Post by Erika »

sounds like my bike... if you don't know what your doing would it be costly to have this done by a professional?
ross46
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Posts: 825
Joined: Fri Aug 26, 2011 9:31 pm
My Bike: zxr 400 l6

Re: Lumpy at low revs (<4000 rpm), fine above

Post by ross46 »

There are 2 posts in the "fuel system" section, one on how to strip and clean your carbs and one on how to set them up, they're just screws at the end of the day, take the carbs off, undo the bolts spray with carb cleaner and thats basically it, nothing too difficult, my suggestion is have a go and get an understanding, then next time you have a problem you can save yourself some money. Everyone on here started in your position
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