ZXR bad fueling low RPM

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Solis560
Posts: 14
Joined: Thu Aug 21, 2014 7:24 pm

ZXR bad fueling low RPM

Post by Solis560 »

Hey everyone,

I've recently had some problems with the ZXR400, it felt very boggy on WOT and didn't like to go above 6k RPM, but it would run decently in the lower RPM range.
Now I've had my carbs ultrasonically cleaned and now it feels wrong in the lower RPM range, needs loads of throttle to get off the line (I gave it throttle and slightly released the clutch to its biting point, this led to a drop in RPM but no feeling of torque), the bike struggles and it makes a sort of BRRRR sound when on the throttle hard. (I have a feeling it might be running on 3 cylinders in the low RPM range).
Above 6K RPM it goes great, screaming to 10K RPM which is what I believe the limiter because of my restriction.
When stood still the engine hangs at ~2000rpm a bit before dropping down to its idle speed.

We've had the carbs cleaned, we've have changed the sparkplugs, all of which were a nice coffee brown colour and we've changed the fuelfilter so far.

Any idea what this could be?

Also I must mention, the previous owner told me he and his mate restricted the bike by changing out the jets.

Thanks!
Last edited by Solis560 on Sun Apr 09, 2017 7:20 pm, edited 1 time in total.
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Miles
zxr400 oc member
zxr400 oc member
Posts: 498
Joined: Wed Apr 30, 2008 11:00 pm
My Bike: ZXR 400 L3
Location: Bangor, Northern Ireland

Re: ZXR

Post by Miles »

Have a look and see what jets are in the bike, see where mixture screws are at and have a look at the needles see if they've been raised etc

If the jets were fiddled with before than chances are they are too small
Solis560
Posts: 14
Joined: Thu Aug 21, 2014 7:24 pm

Re: ZXR bad fueling low RPM

Post by Solis560 »

That might not be a bad idea.
If I were to change out the jets because they are the wrong size, how would I go about deciding which size I need? My bike has an aftermarket exhaust (BOS) and a K&N airfilter I believe.

I'm not sure what the needles do, how do I check if they are raised?

Thanks!
User avatar
Miles
zxr400 oc member
zxr400 oc member
Posts: 498
Joined: Wed Apr 30, 2008 11:00 pm
My Bike: ZXR 400 L3
Location: Bangor, Northern Ireland

Re: ZXR bad fueling low RPM

Post by Miles »

I would reset to standard as per the zxr manual and go from there.

As for the needles, see if their stock. N77S from what remember. If their raised then you will find washers under them.
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