Throttle hesitation

Hello all, after slowwwwwwly rebuilding my 81' kz550 over the summer I finally was at a point to try starting it today. Hooked up my little soda bottle full of gas to the fuel line and she fired right up!

To make a long story short I have been fighting mechanical and electrical problems for quite some time and until now the bike wouldn't even fire. I've replaced coils, plug wires, redid the timing, new manual cam-chain adjuster...the list goes on.

While the bike fired up nicely and idled, it had a serious hesitation when I gave it a small amount of throttle. It hesitated to the point where it would have shut off had I not let off the throttle. I was however able to rev the engine high, it just seemed that under 4k or so rpm it wanted to hesitate/bog down and die.

I did not replace the pickup coils yet, not sure if they are bad and possibly sending a weak spark? Also I need to pull the spark plugs tomorrow after I run it for a little while to see what they look like, maybe I just need new plugs? I'm not sure what the issue could be right now.

If anyone has any thoughts, I'd appreciate the input, Thanks

I would check:

Timing advancer

Fuel bowl levels (clear tube)

vacuum leaks

Clean fuel tank/petcock

If you think it's the ignition pick up coils, try this check(I wrote it for the bigger 4's, but it should work for yours):

Ohm Checking Pickup(Pulsing) Coils

The pickup coils on the Kawasaki’s with the factory supplied electronic ignition can sometimes fail or become intermittent due to heat and vibration.

1.Trace back from where the pick up coils are mounted,(under a right side CD sized cover) locate and disconnect a small 4 pin connector. Using a multi-meter set on OHMS and range of 2K, check between the BLUE and BLACK wires(#1 and #4 sparkplug wires) for between 360- 540 OHMS.

2.For #2 and #3 sparkplugs the wire colors will be YELLOW and RED, again 360-540 OHMS.

3.If the pickup coils are suspect of failing due to heat, they can be stressed using a hair dryer without the need of the engine running.

4.A replacement set of pickup coils might be obtained from a dealer who serviced the police Kawasaki’s.

5. If replacement pickup coils are not available, your next choice would be to order a Dyna “S” electronic ignition system from www.z1enterprises.com It replaces the IC igniter with a smaller module located where the mechanical ignition advancer was mounted.

6. Checking with Kawasaki.com website has determined that the Pick up(pulsing) coils are available . The pulsing coil # is 59026-1133 and replaces the older # 1002, 1012 which were used from the MKII motors until the 2005 P24.

7.Check the small 4 pin connector that the pickup coils connect to for corrosion/loose pins too.

exactly how do you check the float bowl levels? Is it just as simple as attaching clear hose to the bottom of the bowls, raising the hose above the carb body and loosening the screw? I'm not sure where to start looking for vacuum leaks, but I'll start going over everything tomorrow. Also the fuel tank and petcock aren't even back on the bike at the moment, I only started it with the fuel hose running into a bottle of fuel. The petcock was rebuilt and tank was cleaned so I don't think that will be an issue anyway. Thanks

Vacuum leaks can be checked for by either using a spray like WD-40,Brake cleaner,and carb cleaner sprayed on a warmed up engine around the carb holders or the rubber ducting(boots) from the air filter box.

Another method is to use an UNLIT propane torch(less messy this way). Either method if you have a vacuum leak will cause the rpm's to go up. Then the fun begins in ordering new parts.

.

jwe2
I think those TK carbs on the 550 have a similar type of float bowl to those on my CV34s where opening the drain screw allows the fuel to run out the overflow nipple.

In which case the procedure would be exactly as you described.

jwe2 wrote:

Hello all, after slowwwwwwly rebuilding my 81' kz550 over the summer I finally was at a point to try starting it today. Hooked up my little soda bottle full of gas to the fuel line and she fired right up!

To make a long story short I have been fighting mechanical and electrical problems for quite some time and until now the bike wouldn't even fire. I've replaced coils, plug wires, redid the timing, new manual cam-chain adjuster...the list goes on.

While the bike fired up nicely and idled, it had a serious hesitation when I gave it a small amount of throttle. It hesitated to the point where it would have shut off had I not let off the throttle. I was however able to rev the engine high, it just seemed that under 4k or so rpm it wanted to hesitate/bog down and die.

I did not replace the pickup coils yet, not sure if they are bad and possibly sending a weak spark? Also I need to pull the spark plugs tomorrow after I run it for a little while to see what they look like, maybe I just need new plugs? I'm not sure what the issue could be right now.

If anyone has any thoughts, I'd appreciate the input, Thanks

Do you have the stock airbox or aftermarket pod filters ?

I do have the stock airbox with a fresh new filter. Everything about the bike is stock, except for the manual cam-chain tensioner I installed.

I'm about to go start the bike and start looking for leaks, check the resistance of the pickups, etc...I'll let you know what I come up with. I'll try and take some pics of the bottom of my carbs if that helps. Thanks for all the help!

ok so today it didn't want to start as nicely as it did yesterday....figures. It would only start with full choke and lots of throttle, then it would fire up to high rpms and immediately die. I could keep it going by revving it really high, but that was it. did not want to idle or stay running at anything below 4k

Checked the resistance of the pickups. At first I got nothing, zero readings and then infinite. Then for some reason I got the normal reading of 450ish on both pickups, and with my last test I got infinite on both again. I'm going to try out another multimeter just in case, but I think I might order a dyna-s ignition and be done with it. The #2 and #3 exhaust pipes felt less hot than #1 and #4. They definitely were not cold and would have still possibly burnt me, but there was a noticeable difference. Could the pickups be intermittent and causing this problem? That would possibly explain my funny readings.

After reading this complete thread, I don't think you have an electrical issue at all. I think you either have dirty carbs, or weak compression. Did you ever do a compression test ? When you say "rebuild" to what extent is the rebuild ? Overbore ? just rings ? Need more specifics. Did you do a compression test prior and after the rebuild ? Are the carbs clean ?

This is assumption, but I'm assuming when you say pickups, you have a stock transistorized ignition is that correct? If so.

What you're describing doesn't sound electrical to me. It sounds like fuel starvation, and possible air intake leaks. Could just be my fortune, but I've never seen a pickup die in over 30+ years. I suppose they do sometimes.

Here's my short list:
(1) You checked resistance with pickups disconnected from transistor box, correct??
(2) Did you check pickup for voltages with them plugged in and key on? Your book should have what voltage it should have on either side.
(3) Do you have all the air mixture screws at the factory starting position? Tweaking from there is a much simpler job.
(4) Do you have all the inlet nipples plugged off? Air filter in and cap on box, intake boots are properly aligned?

You said you were using a soda bottle for fuel delivery, it's vented I assume. I'm also assuming since it's an 81 you probably have a vacuum assisted petcock on the actual tank, so that could possibly have you with at least 1 nipple not blocked off.