Topic: Help, Bike not running correctly

[greatpenguin]

Ive been working on my bike for awhile now, and cant seem to get it running right.  Any info would be helpfull.

Usually Below 3.4k it missfires pretty bad, when at WOT it stalls, inbetween it runs pretty much ok.  Sometimes it missfires bad entire RPM range and backfires, eventually clearing up.  Last time it did this, I left it at WOT for about 30seconds until it smoothed out.  Then it ran really well for about 20min, then it went back to how it normally is.

Pulled the plugs, they are black.  It smells rich so there wasn't a real need to check the plugs but I did anyways.

Another thing ive noticed is that I can screw in a A/F screw on the carb all the way, and it still runs.  Shouldn't it just die at that point? 

Ive replaced the mainjets, plugs, checked timing, cleaned the points, checked fuel filters.

Any advice, things to check.

[NickC]

What bike?
All stock?
What tune up procedures have been done?

[greatpenguin]

Guess that might be helpfull

Its a 74 CB550.  Its got a 4-1 header and pod filters, then as mentioned its currently got 110 jets in it.  It did have 100 and had the same issues, thought the seals may have been bad and sucking to much fuel.. With the new 110s its no different.

As for tune procedures.. I believe the floats are set right (but maybe not), points were cleaned and set to spec, spark plugs were cleaned and gaped to spec.  Not 100% sure how to check timing, but it didn't look off if it was.  All the jets were jets were soaked and blown out with a air chuck (could that have blown open the jets or something in the carbs to much?  Coil going out? Condensers going out?  Not sure how to really check either of those..

[OldSchool_IsCool]

I doubt its a coil, points, condenser or timing issue.  Usually with ignition trouble, you will see cylinders 1&4 acting differently then 2&3.  Are all 4 plugs sooty?

With powdery black plugs, you are running rich.  Have you had the carbs out?  If yes, did you bench sync them before you put them back in?

[greatpenguin]

Yeah, all 4 plugs are covered in black.  Its def running very rich, you can smell it out of the exhaust.  Ive had the carbs off and alligned everything including matching the slides idle gaps, but not "bench sync'd".  Not sure how you go about doing that.

I thought maybe the seals were bad on the main jets which is why i swapped them out.  Also thought maybe the slow jets had worn out some and are sucking to much fuel, but have not swapped them out yet.

[greatpenguin]

Just read up on "Bench Syncing" guess that is what I did when we matched the slides up.  So that has been done.  However, im not really sure how if that was off it would make every cylinder run rich throughout the RPMs on SOME occasions.

On very few occasions the bike runs like a champ, usually below 3k it misses really bad, and at WOT is stalls.  On other occasions it missfires and even backfires throughout the entire RPM range. Because it doesn't act up the same all the time is why I was thinking electrical?

[Bob Wessner]

Any number of issues could be causing this, carbs in need of cleaning/setting to specs, intermittent ignition problems, etc.

[greatpenguin]

Bump to try to get some more helpfull advice.

[Duke McDukiedook]

So, you measured your floats to the spec height- with what? A float gauge?

[greatpenguin]

Im about at the end of my wits on this one.

I checked the float heights with a small engineers ruler off the base.  Ive set the floats to 21, 22, and 23 (back at 22 now) this never made a difference so I dont believe it to be the floats.  Ive swapped out the points and condensers, and also the coil.. This didn't make a difference.  I checked the timing and its dead on.  Ive tried the 100 mains and 110 mains (I have pods and 4-1) and this didn't make a difference.

Still, its running REALLY rich, and when I open up the throttle it stalls then backfires really bad.  The only idea that I have left is that the needles are set to high?  I haven't tore the carbs apart that far since I got ahold of the bike so im not sure where they are set.  However if no one thinks this would be it im not going to rip them apart.

Anyone have any more usefull information before the rest of my hair gets pulled out? 

[Johnny5]

Is your advancer clean. Sometimes they get gummed up and stick. It's behind your points plate.

[greatpenguin]

Is your advancer clean. Sometimes they get gummed up and stick. It's behind your points plate.

Ah yes, it was in good condition.  I actually swapped one off of a running bike when i swapped the points and condensers to verify it was not the issue also.  I forgot to mention that.

[BVCB650]

Well, you're getting too much fuel, not enough air or your spark is weak. Air filter plugged? Probably not. Carb plugged? Less gas not more. Verify your ignition system is good....coils etc.

[greatpenguin]

Well, you're getting too much fuel, not enough air or your spark is weak. Air filter plugged? Probably not. Carb plugged? Less gas not more. Verify your ignition system is good....coils etc.

I believe this has all already been discussed and checked.  At this point, its either going to be something so simple Ive skipped over it or something fairly complex it seems.

[BVCB650]

Well, it's rich in all cylinders. Too poor a spark could not ignite the fuel like it should. The fact that you can screw in the idle/pilot jets and nothing happens is enlightening. They are probably plugged and fuel is getting there from a secondary circuit. I think you are going to have to pull the carbs for a major cleaning. I had a 550 Suzuki once that cut out at WOT. The stator wasn't charging and it barely had enough juice to fire the points.

[greatpenguin]

For those of you playing along at home, the issue has been resolved.

I took the carbs back apart for the 12th time.  Found out that one of the slow jets had a crack in it right above the threads (Broke it off in the carb and only a tiny bit was shiny so its been pulling gas/air forwhile), I replaced all 4 slow jets.  Also replaced the float needle and seat and the needle jet.  While replacing the needle, I moved it one notch higher to slow the fuel down.

One of the four things fixed the issue, its running like a champ now!