Vacuum petcock / poor performance

Took my 740/4 out for first time in a few days today. Ran fine last week. Within 1/2 mile from home, thing starts bucking and sputtering like she's running out of gas or something (had 1/2tank+). It subsided, I ran my errands, cruised about 7 more miles and until it got really bad, then limped home.

Noticed a nut fell off a bolt to hold a coil on, so I removed the tank and it starts pissing gas all over the place. Reattached the coil, and tightened the others, and drained gas into an can. Pretty much goes without asking that I need to rebuild or clean the petcock, but was this the cause of the bucking/sputtering from flooding the carbs or something?

First start up was normal, and it idled fine. Just crazy lurching through the power band.

I was also thinking a coil may be going bad. I've dealt with that already and that's more of a severe power loss and no idle compared to the iron horse trying to throw me off.

First, remove the screws for the gas cap. I think a vent hole may be plugged, causing the lurching. Do you have the Kawasaki supplied electronic ignition? If so, a pick up coil may be heat sensitive.Read this:

Ohm Checking Pickup(Pulsing) Coils

The pickup(Pulsing) 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,(BEHIND A RIGHT SIDE, CD SIZED ENGINE 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. The 550’s,650’s & 750’s may be backwards to the Z1’s,Kz900’s,Kz1000’s & Kz1100’s.

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.

8. The mechanical ignition advancer needs periodic service too, it's in the area of the pickup coils, mounted on the end of the crankshaft. Some light lubrication on the weight pivots and the moving shaft are about all it needs. A dab of Moly grease or 3-in-one oil will work for this.


Are your ignition coils as old as the bike? They need replacing too, as the coils can break down when hot.

Ignition Coils And Sparkplug Wire Choices

What came with the bike, were ignition coils that even when new were marginal, add years of cooking under the tank in the stop and go traffic, and the coils will probably fail when hot.

Replacement coils can be bought at www.z1enterprises.com I believe “Emgo” is the brand. They also carry the popular Dyna 2.2 and 3 ohm coils, along with replacement sparkplug wires.

Now, you have a choice on sparkplug wires:

1.Copper plug wires with no supression caps (the best choice, but will produce audio noise on Radio’s and TV’s). Not only do the copper core wires deliver better spark, they will also deliver a much longer lifespan - carbon core wires are prone to erratic spark delivery and early breakdown, & short lifespan.

2.Copper plug wires with supression caps(a built in 5000 ohm resistor, that can sometimes fail, like what came with the bike).

3.Copper plug wires with no supression caps, but using resistor plugs(the “R” in the plug number, like B8RES).

4.Supression plug wires with no supression caps.

NEVER use resistor plugs combined with supression caps along with supression plug wires, as now there will be two (2) sources of resistance in the secondary windings of the ignition coils, greatly reducing the spark energy.

Another choice is the Accel 3 ohm coils, with a similar, primary(small wire)electrical connection, using ring terminals as the Dyna ignition coils do. Whatever brand of coil you go with, make sure the primary wires will clear the mounting hardware, as the spacers come awfully close, possibly blowing a fuse. Some riders have replaced the metal spacers with non conductive Nylon spacers, reducing the chance of an electrical problem.

7mm sparkplug wires will fit the stock ignition coils(if they have replaceable wires, indicated by screw off caps on the coils with ridges). The sparkplug wires fit into a port with a brass ”Stinger” that goes into the sparkplug wire or lead(the Brit’s. Canadians, and other countries call the sparkplug wires (“High Tension Leads”).

My ignition system is pretty much frankensteined together. Dyna S ignition that was pieced together from two half working systems. One 3-ohm Dyna coil and one 3-ohm Yamaha coil(the other Dyna was toast). It's been that way since 1 year ago when I was having all sorts of electrical gremlins, but it's run great since then.

I'll check into the gas cap screws and find my Dyna S printout from last year to check ignition pickups tomorrow.

My Vacuum valve was not closing well either. I took apart the diaphragm and stretched the spring out. It would open fine but was slow to return when it was removed and I sucked on it to test it. After I stretched the spring out it closed as fast as it opened.

If your floats are not working correctly or the float valve is worn it won't fully block off the fuel and it can overflow. you should check the overflows on the carbs to see if fuel is coming out of them. When the bike begins to misbehave just pull over and turn it off and yank the overflow tubes off the carbs and see if fuel comes out. My Overflows go to my air box and it sucks the fuel into the engine so it runs rich. My bike tends to idle high when it goes rich though, which I found odd because on my ATC's running rich causes them to bog down.

Also, I found that depending on which coil goes belly up it produces a different reaction, one set will not affect it much while the other will cause a huge loss in power. try swapping the coils and see what happens.

If your coil was flopping around because a mounting bolt fell off it may have been intermittently shorting out against the frame or fuel tank. That could cause the erratic running you described. Ed

Turns out I had a loose bullet connection. Thanks for the input, guys. Guess those two issues were unrelated.

And thanks ironslave, stretching the spring inside the fuel tap seemed to do the trick.

With a bike that's running very erratic, it can be almost many things(sometimes at the same times).

All that bucking from 15 days ago really shredded my rear sprocket. Nearly threw the chain this past Thursday. Lucky I was only 2 miles from home.

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