1980 kz750 popping problem

have 80 kz750 ltd new tires new tabs yada yada and so when i start it up cold it does ok for a bit then it starts smoking and popping out of the left(drivers side) exhaust pipe what i am wondering is is it the coil carb or what i pulled the plugs tested the compresstion for the second time with the throttle open all the way this time and it read 120 all the way across so i know its low but i :blush: ts consistant so i know its not the engine although its low and maybe the timing chain is out of adjustment who knows. another thing is the outside cylinder #1 i think on the left side has some of the spark plug threads missing from the head and the carb for that cylinder drips pretty consistantly so i think its running lean on that carb then overheated that cylinder then the head melted to the spark plug and someone tried to pull it out and pulled some threads with it. so what do you know that will help me fix this? also i was thinking since i live in the northwest and its cold right now i could devise an air scoop behind the engine maybe with a small 12v fan and run some hoses to put in my jacket pants and helmet. any help on this matter would be greatly appreciated this is my first bike and i was born in the 80's when fuel injection was mass produced so when it comes to carburetors i dont know nothing

you may want to check valve clearances to make sure they are all within spec

The cylinder that has the dripping carby will be running rich (all else being equell.check tappets,fit new plugs & see what happens.we already know that the carbs need to be pulled & the float levels adjusted.wayno

120 is about the service limit for compression on 750 twin. It's going to run like crap. I would check valve clearance first. Z1 sells an Emgo coil for these for $36 which is a good idea if you want to have fewer problems in general.

thanks for the help i dont know... i changed the oil on tuesday and it sounded better i guess i will wait until this morning to start it to see if it still smokes as much. also i pulled the #1 plug wire(4 cylinder not twin) so i pulled the plug wire and it zapped me pretty good through the boot and i wasnt even grounded on the bike so i guess i could break down and get a multimeter or i could just test the rest of the wires like i did on the first one i just dont want to affect the hairdo to where its not fixable

If all else fails, you might want to take a look at the smog system. I had a problem with my 82 750-4 with the popping. It started doing it during decel, then go progressively worse. I pulled the vacuum hoses off the carbs and plugged the holes (keep the one tied to your petcock)and ran a hose between the two ports on the valve cover. That took care of the problem. I think the diaphram in the smog assembly was stuck.

Anyways, if the other suggestions don't work, you might try that.

Good luck

Grab a manual and perform the entire maintenence chapter.
Replace your plug wires and caps.
Pull the carbs and clean them out/or have them cleaned and rebuilt professionally.
Re-assemble and ride.

Good luck.

well i replaced the plug wires(the old ones were like sticks) today and while i was at it i fixed the crankcase ventilation it was missing a hose all in all it cost me 8 dollars, so even though when its still cold the idle floats a little when i rev it but the throttle linkage and everything doesnt stick it is just a little slow to idle down after a good rev while warming up. it may not be a big four but its the biggest small four- and you can say what you want about what ltd stands for but at least i know it doesnt have Little Tiny Balls- and by balls i mean ballbearings

donthaveakawman wrote: well i replaced the plug wires(the old ones were like sticks) today and while i was at it i fixed the crankcase ventilation it was missing a hose all in all it cost me 8 dollars, so even though when its still cold the idle floats a little when i rev it but the throttle linkage and everything doesnt stick it is just a little slow to idle down after a good rev while warming up. it may not be a big four but its the biggest small four- and you can say what you want about what ltd stands for but at least i know it doesnt have Little Tiny Balls- and by balls i mean ballbearings

...Dont give it big revs while its warming up dude.

:laugh: :laugh: :laugh: L.T.D.

donthaveakawman wrote: well i replaced the plug wires(the old ones were like sticks) today and while i was at it i fixed the crankcase ventilation it was missing a hose all in all it cost me 8 dollars, so even though when its still cold the idle floats a little when i rev it but the throttle linkage and everything doesnt stick it is just a little slow to idle down after a good rev while warming up. it may not be a big four but its the biggest small four- and you can say what you want about what ltd stands for but at least i know it doesnt have Little Tiny Balls- and by balls i mean ballbearings

Floating (or hanging) idle is a symptom of a lean mixture. It is still doing this after replacing the missing hose?

In case you don't have a manual handy: KZ750 4 Manual

well it has been doin this "floating idle thing" ever since i replaced that crankcase vent tube i would rev it to about 3k and it would float there. i also think the timing chain is stretched it makes a noise going down the road like something making a noise, its not so much grinding or rubbing but ist more of a frictioning, at certain rpms. and the compression is the same on all cylinders but low so i think its just out of time a little and i know it would be a major overhaul to replace the cam chain so i might just go with one of those mechanical tensioners- that is if the guide isnt torn to shreds. i guess if its stretched it will be off reguardless but not as bad.

so i just found out about the clean air system-wow, that could play a major role in the reason this thing is bucking from a stop, i could be wrong but wow. also i installed glass-pack mufflers on the bike. for some reason they like to collect fuel in the fiberglass and then pop out of the exhaust more now than the intake, which was partially due to a crappy spark plug connector-oops zapped myself again. i like when it pops out of the exhaust because it sounds like a paintball bun fight.