Topic: 2 and 3 not firing right...

[mr_jason]

so i'm having some trouble with my bike.  when i start it up, the 2 and 3 pistons aren't firing (at least the headers are cold while the 1/4 headers are hot) the bike runs really sluggish and i have to stay on the throttle to keep it alive and it's like that for a few minutes, then all the sudden, they are firing great and the bike rides perfect.  i was thinking there wasn't fuel going to the carbs, but from what i can tell that's not the problem.  then i though, well maybe there is too much fuel going to the carbs and they are just super flooded and that's why they aren't firing and they "burn off" the excess fuel and then it runs fine, but i checked the floats and they seem to be working fine and i'm not sure what else to do.

i do see fuel overflowing from the 3 carb when i leave the fuel on and let it sit, but not right away, it takes some time (that's why i was thinking maybe it was the floats)

anyone have any ideas?


1976 cb550F with dyna ignition.  it has a 1974 fuel tank off a K (for the looks) with what was a new petcock.  K&N pod filters and a canister exhaust off a GXR.  all of that was on the bike way before i started having these issues.


thanks in advance

[MJL]

2 and 3 are on the same coil. Might have something to do with it. You could swap your 1/4  with your 2/3 without any more work that taking off the points cover, but I would also think there might be something with the choke on 2 and 3.

[Markcb750]

Float bowls overflowing will make the carbs run rich and foul the plugs. particularly at idle.

[1timduke]

To clarify, after the initial rough part, the bike runs and ride perfect after that?   Does it have a smooth idle after it gets over this period, or does it eventually return?

Have you adjusted timing and points, tried new plugs (read 'carb bewilderment' thread), vacuum synced (very important).   Plug connectors tight?   Reading the pugs when they don't fire and after they fire will tell a lot.

If the fuel runs from the carb, then it's most likely a float height problem (at least for that cylinder), another likely culprit is the idle jet.   It doesn't take much to clog them at all.   How does the petcock filter look?   Dirty fuel = unhappy carbs.  

My suggestion would be to attack the carbs last and take care of the ignition part first.   But it may be smart to pull the #3 bowl off and at least get the float height close so as not to leak fuel everywhere (think fire).

Also, let us know which of your bikes it is.

-Tim

[Spanner 1]

I think I would take a close look at the 3-way connector with the 3 black/white wires that feed the coils...it's right by the coils, you'll see it when you remove the tank...also try the straight plug caps ( borrowed from one of your other bikes ! ) I believe one bad cap could  cause both plugs to stop firing as they are paired from the same coil. Good luck.

[jonathantaylor86]

I have a similar problem but mine wont fire at all. I switched the coils thats not the problem. I just got new points and adjusted them with no luck at all. I'm gonna check the float bowls and jets, and vacuum sync this weekend. I'm crossing my fingers on this one.

[magnum56]

I have a similar problem but mine wont fire at all. I switched the coils thats not the problem. I just got new points and adjusted them with no luck at all. I'm gonna check the float bowls and jets, and vacuum sync this weekend. I'm crossing my fingers on this one.

If you're not getting spark (won't fire at all ?), no amount of toying with the carbs is gonna help.

Stay focused on the ignition system, if indeed your descriptioin indicated no spark.

[Scrubs]

I have a similar problem but mine wont fire at all. I switched the coils thats not the problem. I just got new points and adjusted them with no luck at all. I'm gonna check the float bowls and jets, and vacuum sync this weekend. I'm crossing my fingers on this one.

And also check the coils havent come loose at the grounding post - shorting them to the frame. Happened to me more than once.