stumble and fall

Hey all. I wasn't sure where to post this as I am a bit lost. Here goes....I ride a 1984 ZN700ltd A1. Love this thing and very fast(i think) for what it is. Up till now very reliable. From the day I bought it has always seemed to stumble on hard acceleration, and a little at cruising rpms. Over the last winter I pulledit apart and went through it all, plugs, wires, carbs, New Clean gast tank, in line filter.. This season it still seemed to hesitste a little but not as bad. Still in acceleration, and at high rpms.. The bike never has idled right either always reves real high at stop lights and then tries to die on its wayback down. About 2 weeksago me andthe old lady were cruising and out of no where it seemed to almost drop a cylinder. I could still go but barely,at full pin I hardly kept up in traffic and backfire too, and then snap it was fine. Didn't do that for a couple days until last night, we were headed out and it did it several times. We barely made it home. SOme times for a second some times for a couple miles. Tonight I pulled the plugs and found number one to be black, the rest were light grey,coffee brown. Put in new plug and now I'm lucky if I can hit 6,000rpm itgets there and just sputters. Help.wha do you think...????

For an engine to produce power. you need compression, how's yours? 120 PSI is about the minimum for these engines.

You also need fuel, got a good clean fuel flow to all cylinders? Tried some Berryman's B-12 or Seafoam gas additives? Wal-Mart sells both in the automobile oil/additive section.

The Spark should be a hot,and fat anything less is weak making for incomplete combustion.Check the ignition coils input(primary wires) for good energy. A fully charged battery is the place to begin as this ignition needs a good souce of power.

To check the ignition coils, remove the tank, and with a multimeter set on VDC(Volts Direct Current) range of 20,turn the key on. Put the RED probe on the terminal where the RED wire goes.

The BLACK probe goes either on a good frame ground, or the Negative(-) battery terminal. You should read battery voltage. If lower, start checking the switches on the right handlebar(run/stop and start) for corrosion, also inside the headlight housing as this is where many electrical connectors are located.

Are these stock ignition coils? They breakdown from heat and age along with the sparkplug caps and sparkplug wires.

Checked the valve clearances? Your bike probably has the shim under bucket set up requiring the cams to come out to adjust the valves. Get a workshop manual and read up on this procedure.

i'm going to guess the stock ignition is failing or you have a wire chaffing somewhere.
kinda leaning twords wires rubbing somewhere since it's so intermitten.

When it gets cranky after getting good and hot, I would suspect coil, igniter or magnetic pickups.

beaverclever02 wrote:

pulled the plugs and found number one to be black, the rest were light grey,coffee brown. Put in new plug and now I'm lucky if I can hit 6,000rpm itgets there and just sputters. Help.wha do you think...????

One of the many possible causes might be too high fuel level in #1 carb float bowl.

Could perform clear tube test to check fuel level.

Good Fortune!

Had same problem problem on my 79 took tank off and one of the coil wires ( the wiring harness wires) had vibrated loose but was still plugged in to the weather proof connector I plugged it back in and it was good to go. I would also check your timing advance mechanism and clean and lube( I assume it has elect ignition) Hope it helps Grant.

a blackened DRY fouling on the plug is too much fuel, stumbleing on exceleration can be caused by the same- flooding out, a backfire also can be cuased by too much fuel, like patton said check those fuel lvls in the carbs

Sounds electrical to me...

GL.