1978 KZ650 only running on two cylinders?

My Dad and I are trying to get a barn find running. It is running great but only on two cylinders. This is proven by when starting the bike cold it only heats up two of the exhaust pipes.

The bike was running pretty quickly into the rebuilt. Cleaned the carbs and that got the bike running. It ran terrible under about 5000 rpm, but above 5000 rpms the bike was powerful and awesome. It gave hope of a awesome older machine to ride. The carbs needed to be really cleaned, replace some jets, synch.... The timing was done and compression testing showed that each cylinder has about 105-110 pds in each. The bike purrs idling. I have no idea how as it only runs on two cylinders but anyway.

Things checked:

• Carbs - floats are good, synched and new needles and seals.

• Timing - It is running a little bit advanced but not too far out. The mechanical timing advance mechanism is working just fine at higher rpms.

• New plugs - 2 of the plugs have a blackish residue and the 2 on the non firing cylinders smell like gas and are wet after running. Grounding a spark plug shows there is spark on all 4 cylinders.

• Coils - tested them according to the book and both are within spec. What is interesting is the non firing cylinders are not on the same coil but one on each is not working. The cylinders not working (from left to right) are 1 and 3.

I just don’t understand why the two cylinders are not firing? They seem to be receiving the three (air, spark, fuel) needed items. I have a Dyna 2000 ignition that I was going to put on but would rather run it stock if at all possible.

Any help is much appreciated.

Brad Barlage
SLC, Utah

I'm no expert but since no one else has chimed in yet I'll tell you what I would check.

Check plug gap....plus....If those are old plugs I would replace them.

I would be sure those two cylinders are getting a spark while running. I use a timing light to check. Sometimes a plug will fire outside of the cylinder, but not when installed and under compression. I ran into this on my '75 Yamaha DT125 and a lawnmower.

You say the plugs are wet so maybe the float level is set too high on those carbs, flooding the cylinders? You need to check the fuel level in the bowls using the clear tube method....a search will turn up details and a drawing.

Is air filter ok?

If a coil was bad you would get a problem on either 1 and 4, or 2 and 3. Like you said, 1 and 3 are on different coils.

Check point gap and timing, I would get the timing spot on using the static method. Then you can confirm with a light.

If it still wont run right then its time to check valve clearances. You need to do that anyways really, you don't want to be riding it around with out of spec clearances. I believe yours is the shim under bucket, so you get to pull the cams to change the shims. But you don't need a special $50 tool like over bucket shims, so there's the bright side.

A factory service manual is a must, not a clymers or hayes. Don't waste your money, just get the real deal. There is a guy on ebay that sells reprints out of New Zealand.

Probably some other simple stuff I'm not thinking of right now. Maybe some others will add some suggestions.

It sounds like you may just have the spark plug wires on the wrong plugs. One coil (black wire from points) fires #1&4, the other coil (green wire from points) fires #2+3. In the link below is some general info you may find helpful. Ed

kzrider.com/forum/10-new-members/589649-...r-savannah-ga#594587

Do an OHM check of the sparkplug caps using a multimeter. They should read at 5000 ohms, and these will go bad from heat, age, and vibration. When installing new ones, cut about 3/16" to 1/4" off the end of the sparkplug wires for better connection.

Thanks for all the helpful advice. I found that the coils were on the wrong plugs and only sometimes getting spark. The spark would be seen with the eye but would not fire. I pulled the entire electrical system off and checked each component and put it back on. For 30 seconds it ran like a champ, awesome throttle response and purred. Then the right coil stopped working and back to running on two cylinders. Now I know what the problem is and will go forward.

Any advice on getting two new coils or just going with the Dyna 2000? $100 vs $450. I like the idea of keeping the bike stock.

Thanks again for the helpful tips. I'll post photos soon. So excited to get it running proper and back on the road.

If you want to stick w the points ignition, you could get the Emgo coils. Z1Enterprises.com? That would be the about the cheapest option & the Emgos are supposed to be good. I saw some 4.0 ohm coils at Z1 but I'm not sure if they are Emgo.

The Dyna-S is an option for the KZ650. $133 at Z1Ent + the green Dyna coils.

You could install the electronic ignition from a KZ650-CSR + the grey or green Dyna coils.
Most of the 750-4s have the same ignition system as the CSR, but you'd need the advancer from the 650.

Brad Barlage wrote: ....For 30 seconds it ran like a champ, awesome throttle response and purred. Then the right coil stopped working and back to running on two cylinders. Now I know what the problem is and will go forward.....

You may want to verify that it is a coil problem before buying new coils. One fairly easy thing you could do is swap the coils and see if the problem follows the coil and moves to the opposite 2 cylinders. If it does, the coil is shot. If the problem stays on the same 2 cylinders you may have a problem with the points or the wiring between the points and coil. Ed