Number 1 cylinder not firing

[Stan C]

I have a 1981 Honda 900F (I know it is not a 750 but this is a problem that will be common to both). For some reason when I am running my bike I get a miss (popping) through the exhaust which I can hear and also feel with my hand. It is starting to drive me a little nuts as I have tried multiple items to source it.

I have done the following: 1) New Plugs, 2) tested all the plug caps, 3) tested the plug wires, 4) tried replacement coils, 5) interchanged the two ignitors to see if the problem moves (nope), 6) Using premium fuel (Chevron 94), 7) Leak down test from 1 to 4...100/97, 100/95, 100/97, 100/99, 8) Sync carbs, 9) Stock aircleaner, 10) Checked the ground path.. clean and no resistance, 11) Valve clearances are all within specs, 12) Battery is good and fully charged. 13) Timing is perfect,

Did a compression test (bike was cold) From 1 to 4 readings are 120 psi across the board, added oil to each cylinder and it jumped to 145/150 across the the board. While I know this is low it is not low enough to give me a problem with the unit running. I managed to track down which cylinder is was through feeling the exhaust, and removing the plug caps. Number one is the bad guy. I actually had the bike running on 2-3-and4 cylinders while I had the plug out of number one. With the number one plug connected the spark was a deep blue and did not seem to miss a spark. I believe the low compression is due to glazing on the cylinder wall (only 50 kms on a complete rebuild), however this will not effect the missing on the one cylinder, since the other 3 were the same compression and were running fine.

The 50 clicks that are on the bike since the rebuild is a ride I took to start the breakin procedure. Interestingly enough I only got the miss when the bike was under load, taking off from a start and going through the gears about 4000 to 4500 rpm it would miss, but cruising down the freeway at 100 clicks at about 4000 rpm's it would run just fine. If I cracked the throttle the miss would come back. Almost sounded like a backfire, hard to describe what it actually sounds like. Don't know how to put a sound bite on here otherwise I would add the audio, it might help someone find a solution. (If you know how let me know)

Looking forward to your assistance with this pesky issue. Thanks Chris

I recently started my 1979 Honda CB750K after winter storage, and it ran quite well. I did not run it dry like usual before storing it, and thought that I may have an issue. One week later I start the bike and it's running like crap. Rev it up and it revs up but it will not idle smoothly. I splash a bit of water on each pipe and see that number 3 cylinder from the left side as you are sitting on the bike is not running. I suspect some blockage so I take off the float bowl, and have a look at the jets, particularly the idle jet. This can be done with a good flashlight (good lighting is a MUST) a 1/4 inch ratchet with a 1/4 socket and proper philips bit to remove the three screws that secure the float bowl. Anyway, I got a piece of small fuel line and after removing the idle screw and spring, I jambed the fuel line up inside this opening and put some carb leaning fluid into the fuel line and blow it up inside of the idle screw opening. I let it sit and soak for about 30 minutes. I next got an air spray nozzle and aimed it right up inside the opening and gave it a good blast of high pressure air. Do not put the nozzle right up inside, but keep the end of the small nozzle about one half inch away. I put the bowl back on and turned on the gas tap, let it sit for a few minutes and BAMM, starts right up and idles quite well. You can actually remove all 4 float bowls from the bike and clean out ALL of the jets including the emulsifying jet and idle circuit WITHOUT removing the entire 4 carb assembly. I have had the most success at doing this for the fourth time now as described. Be aware that the number 2 carb has an accelerator pump device and it is best to remove the bowl straight downwards as there is a small push pin to activate the pump that runs down into the bowl with small O ring. The carbs on the left side are more easily accessable by removing the starter cover. Hope this helps. I actually found some red lint inside one of the jets so it would seem that you must be carfeul when wiping around your open gas cap. It doesn't take much to mess up the fuel and Hondas do not like dirty fuel. You don't have to take apart what is not broken.