1976 KZ750B Twin Restoration (No Spark)

Hello everyone, my name is Peyton and I just bought a 1976 KZ750B for $350.00 as a winter project. I have grown up around motorcycles and have a 2023 KLR 650 and have had a 2007 KLR 650, and various other cruisers, sport bikes, and the like. I have never had a vintage bike and I feel like I have taken on quite a bit. Here is the picture that I received from the seller, a picture with the motorcycle on the trailer, and now disassembled in my garage:

 

 

 

It has no spark, and the gas tank is in unfortunate condition (very rusty though I think with a good cleaning it will be okay, the petcock is shot). I believe the carb is going to be very gunked up (it has been sitting for years). It has a front light but it is off and most likely broken. The speedometer and tachometer are also off the bike. I also know it will need a new front and rear master cylinder but the rotors are good and the calipers can be restored. I was wondering if these parts should get the bike up and running: (I also have an auxiliary gas tank I will be using until I have this running well)







* Also admins, if this is in the wrong forum section, please let me know! 

I am excited to begin tackling this but I don't really know where to start. The service manual I have a PDF of is confusing and I haven't dived very deep into it yet. 
 

I will try and move all but your intro into the projects section (welcome from the UK by the way) I would suggest you take your time and establish which if any of these components require replacement before you begin throwing money at the problem. The guys here will be able to guide you through checking the various systems

Welcome to what we consider fun.  Take your project one step at a time, it'll be easier to understand each component.  My 2 cents, order your replacements as you need them, or you may end up with extra parts you didn't need and still have to order the ones you didn't think of yet.  (A rule I learned the expensive way on one of my early hot rod projects a few decades ago - still applies).  There are many knowledgeable members here that can help you when needed.

By "no spark" do you mean it won't crank or it isn't getting spark at the plugs?

did it come with an exhaust? can you look into the exhaust ports and see what condition the back of the valves are in? When these engines sit for a long time with the ports open often there will be with an exhaust valve open which can let moisture into the cylinder and can require a top end rebuild to rectify. You can also pull the spark plugs and advance the bike with the kickstarter to look in the sparkplug holes. If you see rust or white oxidization in there thats bad news.

Hey Wookie! Thank you, I think that will be a much better idea to buy parts slowly! I'm excited to learn from you all! 

sf4t7 wrote:

Welcome to what we consider fun.  Take your project one step at a time, it'll be easier to understand each component.  My 2 cents, order your replacements as you need them, or you may end up with extra parts you didn't need and still have to order the ones you didn't think of yet.  (A rule I learned the expensive way on one of my early hot rod projects a few decades ago - still applies).  There are many knowledgeable members here that can help you when needed.

I am still learning how to use these forums. I agree with you. This is going to be a lot of fun. My buddy and I sat down and began slowly removing some rust from areas (like the seat hinge and lock) and began looking over things. 
 

DoctoRot wrote:

By "no spark" do you mean it won't crank or it isn't getting spark at the plugs?

did it come with an exhaust? can you look into the exhaust ports and see what condition the back of the valves are in? When these engines sit for a long time with the ports open often there will be with an exhaust valve open which can let moisture into the cylinder and can require a top end rebuild to rectify. You can also pull the spark plugs and advance the bike with the kickstarter to look in the sparkplug holes. If you see rust or white oxidization in there thats bad news.

I just got finished messing with it tonight. I took your advice (I haven't been able to look at the cylinder yet but I will in the next couple of days.) and found that the coil was completely ruined. The spark plug wires had dry rotted and literally fell apart when I jiggled it. I ordered a new coil today. I also watched a video on the points system and looked at mine. It looks okay, but I am not sure that means it is okay. The motorcycle "cranks" with kickstart but I wasn't seeing any spark when tested at the plug (which would make sense with the condition of the coil). I was looking at the wiring and I am worried with what I saw heading to the right handlebar. I've inserted a picture. The yellow and red wire goes to the coil. Is the brown wire a ground? Why would the previous owner by-pass this? 

 

DoctoRot wrote:

By "no spark" do you mean it won't crank or it isn't getting spark at the plugs?

did it come with an exhaust? can you look into the exhaust ports and see what condition the back of the valves are in? When these engines sit for a long time with the ports open often there will be with an exhaust valve open which can let moisture into the cylinder and can require a top end rebuild to rectify. You can also pull the spark plugs and advance the bike with the kickstarter to look in the sparkplug holes. If you see rust or white oxidization in there thats bad news.

i did look into the ports and it was black (picture below). I didn’t see any oxidization in the spark plug holes. 



 

Is the left exhaust port oily? hard to tell in the picture. what the spark plug look like from that cylinder? you can see how these twins like to stop with an exhaust valve open.

These engines have single phase alternator, so kick-starting with a dead battery can be at best difficult or sometimes impossible, i would not say its an ideal way to check for spark. They will not run/run well without a good battery.

Power for the coil is routed through the handle bar switch as you have found. Its not uncommon for corrosion to degrade the switches thereby lowering the voltage that reaches the coil when its cranking. A common fix is to use a relay to bypass the switches. You can search for "wired george coil mod" on here to find more info. if you can connect a new battery or a battery from your other bike it will be possible to trouble shoot the electrical system.

Do you know what Ohm coil you bought? The listing you showed is for a generic coil.  id have to look it up to confirm but I think stock for points is a 4 Ohm coil, points wear faster with lower resistance coils

BTW I would generally stay away from the lower quality parts as they can cause more problems than the solve - particularly with the carb kits/parts. Its false economy. unless water entered the carbs you probably can reuse everything except for gaskets and o-rings.