Cold Cylinder #2, '81 KZ750 LTD

So as some of you know I have a '81 KZ750 LTD as a little project bike. Recently completed checking the valve clearances and re-shimming. FINALLY got the timing set correctly after checking it 100 times. Decided to fire it up last Thursday. Started right up and sounded fantastic. Took out around the neighborhood for a ride. Road great. Pulled strong when accelrating. Turned into my neighborhood to head home and the bike started to sputter and then died. No power when I tired to restart. Ended up being a super easy fix, the RR sensing wire (red/white) came loose from the starter solenoid so the battery wasn't even charging. Reattached the wire/bullet connector and measured the voltage at the battery with the engine running and it was around 12.8v. It was reading 12.0v before the fix. 

So, after getting that fixed I tried to restart the engine. Turned over great and was running/idling, but sounded off. Checked the manifold pipes and cylinder #2 was just warm and not hot like the other 3 cylinders. So long story short I am trying to figure out what to check. It hadn't even been 24 hours since the ride and wire fix. So not sure what is going on at this point all of a sudden. So I am back here in the community or an assist. Love it here.

Could be something simple like a loose or faulty spark plug wire, a faulty spark plug, or some dirt got shaken loose in the fuel tank and is clogging the carb.

If the battery is run down to the point of running poorly, it needs to be charged up.  Best to use a remote battery charger, not the on-board generator.

With a properly charged battery, put your volt meter on DC, put the probes across the battery, and rev the engine to 4 or 5000 rpm.  A properly functioning charging system should put out between 14-14.5 volts.  If lower, you have a problem.

spark plug wires and ignition coils: original or new? at the minimum. I would redo the plug wire connections. the spark plug wires unscrew from the coils and caps.

I pulled the #2 spark plug, grounded it on the valve cover and hit the start button. Saw a nice thick white/blue spark. So spark is good. I then, just because, pulled the spark plugs and checked the compression (engine not at temp). I got 100 psi in each cylinder (would expect higher if I was at temp). 100 psi seems where it should be when starting. I am going to pull the carbs......again......and clean #2 to see if that helps.

The pilot jet and bleed pipe have tiny orifices in them, and they easily clog.

I pull one strand from a stiff wire brush, and use that to push through any crud that may be blocking the hole.  Hold them up to a light, and make sure you can see through them, end to end.



 

Nessism wrote:

The pilot jet and bleed pipe have tiny orifices in them, and they easily clog.

I pull one strand from a stiff wire brush, and use that to push through any crud that may be blocking the hole.  Hold them up to a light, and make sure you can see through them, end to end.

 

Hey Ness. I did that based on a previous reply from you. This cold cylinder happened after doing that cleaning then taking the bike out for a test ride. Could it have clogged again? I used a set carb cleaning wires that I had bought previously when I rebuilt the carbs.

When you pulled off the float bowls, did you see any rust specs in the bottom of the bowl?  If so, tank rust is likely the problem.  And if you installed a secondary filter, be sure it's not the paper type that causes flow restriction.  

From what port are you running the vacuum for the petcock from. Not saying this is your issue but have seen a small tear in the petcock diaphragm sends fuel down the line to the carb running the petcock and flooding that carb with more fuel than intended, which can make it run cool.