Topic: Running rich and missing a cylinder

[khardrunner14]

71 CB750 K1 with stock set up except for 4-2 pipes that seem like they would flow better than stock...

1) needle clip in the middle position
2) fuel bowls set at 26mm measured from gasket to top of float (carb upside down)
3) air screw 1.5 turns out
4) good spark everywhere and timing/points set nicely
5) main jets all 120's original parts

Every plug is reading rich and the bike runs like it. Cyl #1 fires rarely. When I pull that plug there is gas on the plug tip. The bike seems to run best at WOT, then I get all 4 cylinders.

I have the carbs off the bikes so what should I do? I do have keyster replacement parts available.

[flybox1]

2) fuel bowls set at 26mm measured from gasket to top of float (carb upside down)

best to redo this with the carbs on their sides.
if the carbs are upside down, the weight of the float will compress the float valve spring, allowing the float to rise higher than intended (when right side up) before the float pressure closes the float valve. this increases fuel height and can cause rich running.
recheck with the float tang barely touching the valve spring needle and adjust accordingly.

if still running rich, turn your airscrew out more

hold off on the keyster parts.  they have been known to cause a whole separate set of problems.

set your valve lash lately?
do a bench synch of carb slides?
do a vacuum sync?

[khardrunner14]

I did set them while on their sides for the reason you mentioned. Also just did valves and a sync, though that was difficult to do. With the dampener in place the readings were so low that I could not use them and without the dampener it was really bouncy.

As for the air screw, doesn't that really only effect the idle circut? Also, I have that out 1/2 a turn more than it should be with no change. I think that would indicate the problem lies elsewhere.

I'll try the sync again since the bike is running better than before, but it will still be hard without #1 firing.

Good thoughts! Anything else?

[flybox1]

does #1 fire at all, or intermittently?
what are your compression readings ?

[khardrunner14]

#1 goes at times, but usually only at WOT. Previously I was struggling with getting #2 and #3 firing and 1 and 4 were perfectly fine (about a week ago). After cleaning the plugs and re-setting the floats #1 won't fire well.

Compression #s were solid, all within 10%. I think they were in the 140 range cold if I remember right. I'd have to try to find the paper with them on there.

[flybox1]

sounds more electrical than a fuel/air issue. 
maybe #1 plug is not getting discharge from you coil.
when you pull the #1 plug and rest it against the head during idle, do you get a good spark?
better spark w higher rpm?

get a points file and go to work. re-gap your points.
recheck your timing at idle, and advance.
check coil and spark plug wire/cap. 
maybe even trim #1 plug wire and reinstall cap

[khardrunner14]

I get good spark and just did points etc. The other thing is, #1 was a solid cylinder before I did the fuel float readjust. Also, that wouldn't have any effect on the richness of other cylinders would it?

[flybox1]

other thing is, #1 was a solid cylinder

?
need explaination....

[khardrunner14]

About a week ago I had #1 and #4 solid with no 2 or 3. I fixed that (electrical and fouled plugs) and had all 4, but it was running really rich. Tried the float bowl adjustment and lost #1, the others are still rich. I adjusted #1 to have more gas in the bowl with no better results.

[flybox1]

spark-air-fuel
spark
battery voltage, coils, timing, points, plugs.  you say they are good. 

fuel supply
did you ever do a bench synch of the slides when the carbs were off?
Think ya need to get your carb settings back to stock. recheck all float heights, passageways, and your slide settings. 
raising float height will richen
if you do the clear tube out the drain screw test, the fuel level should be 4mm under the bowl gasket seam.

air
when you had all 4 running, but also had a rich condition, did you at that point try turning out the AF screw, or removing the airbox to lean it out?  new or old air filter?

[khardrunner14]

New air filter.

I'm going to check carb specs again. I don't know how to do the clear tube float test. Do I have to search for it?

I never removed the box or filter to lean it out. I did try to take the air screw out (hence why it's at 1.5 turns) but no luck there.

[flybox1]

measure the ID of the float drain screw hole.
go buy 3' worth of clear plastic tubing with an OD just larger than what you measured.  i think 1/4" is what i got. cut into 2 equal length pieces.
with a heat gun, or open flame, heat the center of each, while you stretch the tubing.
the stretched area will shrink in size, and if cut in this smaller spot, will give you 2 pieces with smaller OD ends that can be screw'd into the bowl drain holes.
repeat with other 1.5' section.
now you 've got 4 pieces, small ends screwd into each drain screw hole.
position the tubing so it loops up next to the bowl gasket seam.
secure with a rubber band, tape, whatever works.
turn on your fuel, and see the level in the tube.  if its high or low (compared to 4mm below the gasket seam level) you need to adjust the float tang up or down on that carb.

hope this helps you diagnose fuel level discrepancies.