Sudden change to terrible performance

I cleaned my kz400 carbs (which already looked clean) and replaced both torn diaphragms. Put them back on the bike on saturday and after a little struggle getting her started (I just don't think the bowls were filled...maybe the "prime" setting is broken because it eventually started on the normal setting), it ran great. It ran the best it has since I owned it...strong pull and could get good speed. Maybe still a pinch of a lean condition as coming off the throttle to a stop occasionally had some pops in the exhuast.

Started up sunday morning reasonably well, rode on the freeway a bit followed by a stop for an hour, some more freeway, and then some stop-and-go city traffic to my office. It seemed great for this time as well. I went into the office for an hour, came out, and the bike was acting horribly. Had a rougher idle, wanted some choke and has no power on the low end. You can feel it kick into gear at maybe 3.5/4k and it has power although it doesn't necessarily sound good. Getting her moving from a stop though requires me to pump the clutch and try to keep the revs up (but it doesn't really like it until full throttle. Lots of back firing and if I put my hand on the carbs, I can feel it backfiring back into them (which can't be good). It just bogs down really bad at low RPM and then you can feel it all of the sudden pick back up past a certain RPM On the road back home going about 50, I couldn't really get any acceleration in 5th or 6th gear.

I noticed it was a little low on gas and switched to reserve which didn't make it better...put in 2.9gal (how big is the tank? my last fill was more like 3.1) and switched back to normal and still no improvement.

It still idles ok without choke and I tried spraying wd40 at the carb holders and air intake boots and didn't see any change in idle.

What do I need to check next? it literally sat for an hour after working great and went bad.

do the clear tube test (fuel level)
made a BIG change in my bike starts right up no stumble
just an shot

Get the bike level and drain the float bowls into a clean clear container, looking for Junk. Did you clean your tank and petcock?

I'll get some clear tubing and try those things out.

Here's a video I recorded of the sound the bike is making on a short ride (it had already been running for a little bit, this wasn't a fresh cold start.

I start moving at about 0:10 and you can hear the engine finally open up at about 0:20. There are several more starts and stops before I shut it off at around 3:50.



Can you tell anything from the sound it makes?

Sounds like a plugged up low speed Jet/ Pilot jet.

Any crud/rust in the fuel tank? It does not take much to plug up the metering holes in the carbs.

You may also want to check your Points, how old are they and what is the Gap/ Dwell?
www.z1enterprises.com/Ignition-Kit--Kawasaki-KZ400-4477.aspx

ottothecow wrote:
Started up sunday morning reasonably well, rode on the freeway a bit followed by a stop for an hour, some more freeway, and then some stop-and-go city traffic to my office. It seemed great for this time as well. I went into the office for an hour, came out, and the bike was acting horribly. Had a rougher idle, wanted some choke and has no power on the low end.

Mine used to do that when there was crap in the tank that would work it's way down and plug a jet:

Fuel system clean?

Good inline fuel filters in place?

"I went into the office for an hour, came out, and the bike was acting horribly.".
Almost sounds as though someone jacked with your KZ...
Might want to check/verfiy there isn't something stuck down the exhaust pipe blocking flow.

First thought outside of gunked carbs came to mind is the points with emphasis on the condenser (ignition).

Check plug wires/plug caps.

Ok, I will look into this. Thanks

I don't think the points are very old (from the spare/old parts I got with the bike, it looks like they were replaced) but I have no idea what the gap and dwell look like.

Tank looks visibly clean but I haven't taken out the petcock and I don't have an inline fuel filter (any suggestion on one to buy if I should have one?).

I am thinking this is probably something stuck in one of the carbs...but it wouldn't be a bad idea to become familiar with these other things while I try to fix it.