77 KZ650. 2 Cold Pipes, Good Spark, Dreading Carb removal.

The backstory is, i left the bike sit too long.
It now seems like its only running on two cylinders. Only pipes 1 & 2 get hot.
I checked the plugs - they are good.
I changed the fuel filter.
I checked the coil Check am getting good spark on cylinders 3 & 4 but the exhaust pipes only get warm. Held  3 & 4 wires with the spark plugs in the boot, against the engine and saw good spark.

Am I correct in thinking its a fuel delivery issue in the carbs? and why would only 3 & 4 passageways from the carbs get blocked?

I may have to take out the carbs. The bike still has the airbox. Ive heard it can be a challenge to remove the carbs. Any ideas? After this I may swtich to airpods!

FWIW. I had an intermittent firing problem on #1 & # 2 and had what I thought was good spark, so I ruled out spark.  But redoing the spark plug wire connections solved the problem. My motorcycle is a 1981 KZ650-CSR w stock electronic ignition & the plug wires can be unscrewed from the ignition coils.  

Carburetor removal. Hard airbox ducts can make it difficult to remove the carburetors.  If yours are hard, get new ones, then cut out the old as it's possible to break the airbox if the ducts are rock hard.  New ducts should be soft & flexible.

wrote:

FWIW. I had an intermittent firing problem on #1 & # 2 and had what I thought was good spark, so I ruled out spark.  But redoing the spark plug wire connections solved the problem. My motorcycle is a 1981 KZ650-CSR w stock electronic ignition & the plug wires can be unscrewed from the ignition coils.  

Carburetor removal. Hard airbox ducts can make it difficult to remove the carburetors.  If yours are hard, get new ones, then cut out the old as it's possible to break the airbox if the ducts are rock hard.  New ducts should be soft & flexible.
 

Im super confident its the carbs because the only think i did that caused this problem is let the bike sit. Def getting good spark. And I was thinking just as you suggested, to get new boots and cut the old ones out to make things easier.

thanks for responding.

You would do well to go through the carbs completely, and replace all the O-rings.  No sense in shortcutting now.

Before solving the problem, I thought it was the carburetors & went ahead and did the complete disassembly & cleaning. It wasn't that hard:  the same thing is done 4 times on a lot of stuff & most parts only go back one way, so it's hard to mess up.  Previously I had removed the float bowls & some of the parts under there a couple of times, so that was some handy practice.  Doing the overhaul is an opportunity to see exactly what you have. I've heard of mismatched jet needles & main jets, that sort of thing. or even missing parts.

Story of my life. I have too many bikes (or so the wife tells me) and if I let one sit for too long it will be hard to start and won't run without choke. I pull the carbs and sure enough, the pilots are plugged. When will I learn? One thing you can try is some seafoam in the tank and just let it run for a while a few times. It might clear out on its own. Otherwise, pull them out (new air boots make this job much easier) and verify jets as martin_csr suggested and clean the carbs really well. 

I tried the seafoam thing, no dice. So i will be pulling the carbs. I did order new carbs boots, but the ones on the bike are pretty OK. I will heat them up with a heat gun, and if they arent damaged in the process of carb removal and reinstall, then I will send the new ones I ordered, back to the seller.

With today's gasoline you need to start the motor once a week to avoid plugging jets (KZ650 with 750 motor/CVK34 carbs) a fuel filter from the tank to the carbs is a big help.

I had no time to ride this Summer as my Son bought a house, so I would start my bike about once a week. I think I only put about 220km on it, rode it to my annual meet and back then parked it, so it sat there for 3 months.

I take the carbs off with no issues as the rubber are new, slip them thru the air box holes. I can also make jet changes by dropping the float bowls but I have smaller hands.

Recently drained the carbs and blew them out to store the bike, if you don't use compressed air they can get plugged pretty easily.

wrote:

With today's gasoline you need to start the motor once a week to avoid plugging jets (KZ650 with 750 motor/CVK34 carbs) a fuel filter from the tank to the carbs is a big help.

I had no time to ride this Summer as my Son bought a house, so I would start my bike about once a week. I think I only put about 220km on it, rode it to my annual meet and back then parked it, so it sat there for 3 months.

I take the carbs off with no issues as the rubber are new, slip them thru the air box holes. I can also make jet changes by dropping the float bowls but I have smaller hands.

Recently drained the carbs and blew them out to store the bike, if you don't use compressed air they can get plugged pretty easily.

Use a fuel stabilizer and your problem will be solved.  My 750 doesn't get ridden much these days, but with Marine Stabil, it always starts right up when I want to take a ride.

wrote:

wrote:

With today's gasoline you need to start the motor once a week to avoid plugging jets (KZ650 with 750 motor/CVK34 carbs) a fuel filter from the tank to the carbs is a big help.

I had no time to ride this Summer as my Son bought a house, so I would start my bike about once a week. I think I only put about 220km on it, rode it to my annual meet and back then parked it, so it sat there for 3 months.

I take the carbs off with no issues as the rubber are new, slip them thru the air box holes. I can also make jet changes by dropping the float bowls but I have smaller hands.

Recently drained the carbs and blew them out to store the bike, if you don't use compressed air they can get plugged pretty easily.

Use a fuel stabilizer and your problem will be solved.  My 750 doesn't get ridden much these days, but with Marine Stabil, it always starts right up when I want to take a ride.

 

Had that mixed in the tank of no ethanol fuel.
My main issue was the choke plungers need done, carbs are removed for replacement seals
and other work. Looking forward to Spring time.

wrote:

With today's gasoline you need to start the motor once a week to avoid plugging jets (KZ650 with 750 motor/CVK34 carbs) a fuel filter from the tank to the carbs is a big help.

I had no time to ride this Summer as my Son bought a house, so I would start my bike about once a week. I think I only put about 220km on it, rode it to my annual meet and back then parked it, so it sat there for 3 months.

I take the carbs off with no issues as the rubber are new, slip them thru the air box holes. I can also make jet changes by dropping the float bowls but I have smaller hands.

Recently drained the carbs and blew them out to store the bike, if you don't use compressed air they can get plugged pretty easily.
 

mine has a fuel filter between the single line from the tank to where it connects to carbs 3&4. thats the only fuel line from the tank. There arent two.

wrote:

wrote:

With today's gasoline you need to start the motor once a week to avoid plugging jets (KZ650 with 750 motor/CVK34 carbs) a fuel filter from the tank to the carbs is a big help.

I had no time to ride this Summer as my Son bought a house, so I would start my bike about once a week. I think I only put about 220km on it, rode it to my annual meet and back then parked it, so it sat there for 3 months.

I take the carbs off with no issues as the rubber are new, slip them thru the air box holes. I can also make jet changes by dropping the float bowls but I have smaller hands.

Recently drained the carbs and blew them out to store the bike, if you don't use compressed air they can get plugged pretty easily.

 

mine has a fuel filter between the single line from the tank to where it connects to carbs 3&4. thats the only fuel line from the tank. There arent two.

Not possible. This bike would have never run. Your only feeding fuel to two of four carbs. Needs to be another fuel line feeding the tee between 1&2 carbs. Post a picture of fuel line routing.