blackened plugs on 1 and 3 cylinders

Hi everyone.

I inherited a really nice 1977 B1 Kawasaki KZ650 from a relative who bought the bike new in 1977, way before my time. My uncle took great care of the bike and 2 years ago had the top end redone and the carbs. since 2024 he only put 100 miles on it.

I got possession of the bike a month ago and ive tested it. Cylinders 1 and 3 keep blackening the plugs. Strange because he had the carbs redone twice for kicks  in early 2024. Should run fine!

He did tell me the bike fell over in the garage, landing on the engine guards, so maybe that did something?

All electrical has been gone through, timing and spark are fine so im guess carbs huh?

Alex

Welcome to the forum Alex.

Plugs 1 & 3 are on different coils so electrical issue is unlikely.
Things that can cause black plugs are:-

Plug gap too small causing a weak spark. 
Worn valve stem oil seals. 
Rich mixture. 
Worn cylinders/rings creating low compression resulting in poor combustion. 
Incorrect valve lap again causing low compression and poor combustion. 
Too cold plugs spec. 
Worn and choke seals. 
Fuel bowl level too high. 
That said start with the easy stuff. 
Which carbs do yo have? Vm22 or Vm24? Pumper or normal? 
Do you have fuel pilot screws or air pilot screws or both fuel and air pilot screws? 
​​​​​​When we know which carbs you have we can advise settings. 

 

Hi and thanks for responding. REALLY nice bikes you have!!

Im not sure of the carbs but my uncle has old pics of when he worked on the bike. I asked him and he said "they are the original carbs for the year 1977 B1 KZ650, Mikuni. I'll have a look when I get to the bike. But in the meantime, here are old pics my uncle had of the carbs.

He is short on patience because he is battling a health problem, but when I talked to him briefly this morning, he said:

The top end was rebuilt 2 years ago with seals like viton etc and the bike has only had 200 miles on it since then.
The Carbs were rebuilt at that time too, with keyster kit or whatever was the best kit at the time, not aftermarket junk
Spark plugs were new
All of the electrical and timing was gone over last week.

The bike runs, but you can tell its not getting good power and those two plugs are black.
Ive searched the forum and see many ppl advise against this, but Im putting on pods.
The airbox makes a devil of a time trying to get the carbs out. My Uncle was going to do exactly that before he put the bike away.
I once helped him change the carbs and my hands were bruised from all of that.
With pods, dealing with the carbs will be much easier in terms of access.

   

Commonly overlooked is    Are plug
wires on the correct cylinder ?

Those carbs are Vm24ss airscrew carbs.
The first and easiest thing to check is the pilot circuit airscrew adjusters (circled n red). 
The should be roughly 1.5 turns out from lightly seated. Screw them in to richen the mixture and out to lean the mixture. 
I would advise against changing to pods unless 1) you know what your doing as this would involve some jet changes and adding air corrector jets and 2) ensuring the pods you buy are top quality from the likes of k&n. 

If it were not for the top end rebuild ( if it was done correctly ) i would have suggested leaking valve stem seals etc as the possible cause of the sooty plugs but ruling that out it may likely be due to leaking choke plunger seals causing rich running which i can repair and running pods requires fitting these air corrector jets to ensure smooth off idle running.
Air corrector jet kit.Kawasaki Z1,Z650,Z900,Z1000,Z1R.MK2, MIKUNI.LEDAR.PODS.K&N | eBay

Hi.

Yup pretty sure the firing order is correct. I even searched the forum to see what has been said on the topic.

thanks for your help. all advice is appreciated

I found my uncle's maintenance logs for his cars and bikes. It seems like he has had a problem on cylinders 1 and 3 fouling, going back to 2019!!! His solution was to turn the screws all the way out and he left it at that because he was frustrated.
Weird because the carbs have been rebuilt and the top end, yet the problem keeps happening. Maybe the engine is crap?

Warren3200gt wrote:

Those carbs are Vm24ss airscrew carbs.
The first and easiest thing to check is the pilot circuit airscrew adjusters (circled n red). 
The should be roughly 1.5 turns out from lightly seated. Screw them in to richen the mixture and out to lean the mixture. 
I would advise against changing to pods unless 1) you know what your doing as this would involve some jet changes and adding air corrector jets and 2) ensuring the pods you buy are top quality from the likes of k&n. 

 

Thanks for your thoughts on this. Sounds like you know what youre doing and you have a lot of great bikes. Based on what you have said, I will keep the airbox and not change to pods.