Topic: #3 cylinder will not fire

[Clutch Cargo]

I took my 76 CB750K6 out for its maiden voyage on Saturday and I can’t get cylinder 3# to fire.

I rebuilt all four carbs over the winter and also had the head re-done.

The timing and dwell are right on.

I am getting spark from #3 when the plug is out and shorted to the block.

When I switch #2 and #3 wires, the problem stays at #3.

There is 25K ohm resistance from the tip of #2 to the tip of #3.

I changed the spark plug in # 3 – no change.

I took out the bowl drain plug for #3 carb and there was plenty of gas in the bowl.

I popped the bowl and the float and valve/seat seem to be working properly.

There is 130 lbs of compression @ #3.

I even took off the tappet covers for #3 to make sure the valves were OK – no problem here.

I can hold my hand on #3 exhaust pipe and it never heats up.

The only thing that I haven’t done is balance the carbs – I’m waiting until all four cylinders fire.

I’m not sure what else to try. 

[736cc]

is the #3 plug getting wet, sooty or dry?

[TwoTired]

On speculation that #3 isn't getting fuel, try this:
Kill switch in off (no ignition)
Fuel petcock on
Choke full on
Throttle at idle
Get 10-20 revolutions of the crankshaft.

Each spark plug you remove should be wet with gas.  If #3 is dry, you have a carb problem, Idle circuit.

You can repeat the test with throttle wide open to test main jet flow.

Cheers,

[Steve F]

Is the plug wet or dry when you pull it out?  Is it even getting fuel?  Floats and such being set, I'm guessing clogged main jet if the plug is dry.  Gas fouling if the plug is wet.
Just my $.025 worth  

[Steve F]

First 3 answers posted within 2 minutes of each other, we were all answering at the same time 

[Clutch Cargo]

Pretty sure that #3 plug was wet when I pulled it the first time.

I will try the above suggestions and report back when I get back in town on Thursday.

Thanks for all of the responses.

[Clutch Cargo]

I finally got the opportunity to tear into this mis-fire issue on the 15th.

The main jet was OK - removable with carbs on the bike, however I had to take off the carb assembly to get at the slow jet. 

There it was - an obstruction in my brand new slow jet. The original slow jet is back on and I will re-assemble the carbs and air box later this week.

Mike