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Discussion Starter #1
Bikes had an idle problem since I bought it 3-4 years ago. I recently replaced the washers and orings since some of them were bad. I started off with the mixture screws at 1.5 turns. Bike started very easily, but the exhaust had a super throaty sound, like a bog, and the bike wouldn't get over 77mph, and wouldn't red line past 3rd. Was also backfiring from time to time, mainly when starting.

I then tried 2 turns, everything was pretty much the same, only I was able to make it to about 83mph. I then tried 2.5 turns and the bike was hard to start.

Today I adjusted the floats to between 14-15mm, and set the mixture screws back to 2 turns. Only thing that changed was I was able to get the bike up to 92mph wot in 6th gear. Actually hit that speed in 5th, and no gain after switching to 6th. Bike still sounds the same, and backfires when starting. Still won't red line past 3rd or 4th, and even in 1st-3rd, it takes longer than it should to get to red line.

Bike has the kleen air/float bowl mod. The way it was setup for the past few years, the air box had one hose connected to the carbs, one was blocked off, and two smaller hose were open and not connected to anything. Ran fine this way, other than the bad idle. Today, I blocked off all hoses except for the one going to the carbs. No change, still sounds bad, and doesn't pull at all.

I have checked, double checked, and triple checked that no fuel lines are pinched, and all 4 plugs are getting spark. Only other thing that was done before it started running like this is I took the ignition apart because there was an intermittent contact problem where if the key wasn't just right, the bike would have no spark. I cleaned the contacts, and the key works fine now.

Not sure where to go from here, as the bike ran strong before the new orings.
 

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Discussion Starter #2
Hoping someone can give me some insight here, because I am getting nowhere with this bike.

2 months later and still no change. So far I've:

Cleaned the carbs more than a dozen times in the ultrasonic, and then blew out with air.
Changed the plugs. Have spark at all cylinders.
Changed the ignition switch because it was loosing contact on the resistor pin causing a no spark situation if the key wasn't just right..
Changed all fuel lines, and the filter.
Smelled pretty rich so I set the floats at 13mm today.
Have set the mixture screws everywhere from 1.5 to 2.5 turns out.
Carbs sync'd after each change.
Good compression on all cylinders.

Only other thing I can think of is the fuel pump may be weak. I doubt this though since I did away with the stock pump, and replaced it with a solid state electric pump awhile back. I'll see if I can find an attachment to hook up my fuel pressure meter to it today.

Bike is backfiring every 15-30 seconds or so at idle, popping lightly while accelerating, power is lacking overall, top speed is horrible, and the exhaust still has a very throaty sound to it. Kinda sounds like a more powerful 4 stroke dirtbike.

The bike ran fine before getting parked for a couple months and replacing the mixture screw o'rings, other than the idle (which is still a problem), and it was getting hard to start, which happens every year or two, and changing the plugs always cured it.

I'm quickly running out of things to check for, and the bike is close to being dumped off the back of my truck, and becoming an insurance claim at this rate.
 

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Are all the holes under the intakes (where you hook vacuum gauges) all blocked off? Is the carb vent line connected to the airbox? Are the spark plug wires in good condition? No corrosion in the ends?
If this all checks out, I would look at float height. I would set it at 14-14.5mm to lean it out a bit. Make sure when setting them that the tang just touches the pin in the float valve. Sounds like it might be bogging due to excessive fuelling. Would also explain the backfiring. Are the float valves in good condition? Seats/o-rings not leaking? Pilot screws will be somewhere between 1 3/4 turns and 2.5. Are they assembled correctly with the washer/spring/o-rings?
 

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Discussion Starter #4
Thanks ninjanut. All vacuum lines under the carbs are blocked, and the carb vent is ran to the airbox. Plug wires look good, and no corrosion. Float height was at I believe 14.5 or 15mm before today, but not 100% sure as it's been a couple months since the last time I adjusted them other than today. Float valves were replaced last season, and no leaks. Mixture screws are at 2 turns right now. The mixture screw setup is spring>washer>o'ring.
 

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Does the bike start and idle properly now? Does the problem only occur under load or once rolling? If it won’t pull past a certain speed/ load, it could be in the needle circuit or vacuum diaphragms.
 

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Discussion Starter #8
It'll start and idle ok, but the rpms will hang near 4k for a few seconds when I blip the throttle. Same problem as before replacing the old worn and missing o'rings. If I turn the idle down enough to where the rpms no longer hang, it's too low to idle on it's own.

The bike seems to rev ok in neutral, although maybe a slight hesitation. The power loss is noticeable across the whole range, but much more so up top. One of the diaphragms did have a pinhole in it, has been that way for awhile now, but never seemed to have any ill effects. I went ahead and replaced it anyhow, but no change. I have washers to use to shim the needles, but there are none currently being used.

I don't have an attachment for my fuel pressure tester that'll let me test the pump, but I'm fairly certain that it's fine. I plan to reset the floats using the fuel level, rather than a set float height, but It won't be until tomorrow or Monday. Today's my anniversary, and tomorrow I have a gathering for my gf's brother who's recently retired from the Army, and has moved back home.
 

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If the idle hangs, you have a leak somewhere. Check around the intake rubbers and make sure all the diaphragms are intact and not pinched. Caps set on correct and tight. Also check to make sure the tiny bleed jets are in the diaphragms. They are located in the little “ear” at the top sealing edge.
Another thing to check is that the spring seat is not covering the hole in the slide. Check the spring to make sure it isn’t bound up as well. Try lifting the slides and see if they move up and down smoothly.
 

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Discussion Starter #10
Got a moment to look at it. I've gone through 3 or 4 cans of spray so far, but have been unable to find any leaks. Diaphragms are in good shape, and seated properly. Bleed jets are in place and clean. Springs are not binding. Holes in the slides are unobstructed, and all slides move freely. Caps could be an issue. One of them has a broken mounting tab. Been like that for a year or two. Never had an effect on the way it ran though, and the hanging revs were there before the tab got broke. Trying to source a replacement at the moment.

Have not gotten to the fuel levels yet. I tested the primary on both coils. Both are reading 3 ohms. I believe spec is 1.8-2.8. Tested the secondary on each coil, and got 14.5-14.7k.
 

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Discussion Starter #11 (Edited)
May have narrowed it down a bit. I noticed that if I pulled the plug wire for cylinder 1 or 3 while running, the bike would get very rough and die right away. If I pull the wire from cylinder 2, the bike would run the same for a couple seconds, then get rough and die. However, if I pulled the plug wire from cylinder 4, there was no change in the way it ran at all.

I then realized that after having it apart for a bit, I got the wires crossed when putting it back together. I had one coil on cylinders 1-3, and the other on cylinders 2-4. I changed it to 1-4, and 2-3, and now the bike sounds and revs MUCH better, but now it's cylinder 3 that has no effect when the wire is pulled. I even swapped the wires between 2-3, and the issue stayed on #3.

Definitely seems like an ignition related issue, but I'm stumped.
 

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Discussion Starter #13
Update: Took the bike for a ride, and it rides and sounds great. Pulled hard to redline 1st-5th, and was still pulling through 6th, but I had to let off due to traffic. Seems very strange that it can run like that, yet I can pull the #3 plug wire, and have zero change to the idle.
 

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Discussion Starter #15
They've been cleaned many times, but that's still a distinct possibility. It also dawned on me that all 4 carbs have stock 38 pilots. The bike has a D&D slip on, and has the mesh removed from the air filter. This may just be why it always seems lean at idle, and the rpm's hang. Not sure what size to try. Maybe a 40?
 
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