Topic: breaking up and back firing all of a sudden.

[Brandotheamazing]

So I fixed the ignition switch yesterday (76 cb 550 ss) and took the bike for a ride, rode good, like it had before the switch problem. Today, take the bike out for a bit, rides good, get gas, rides good, go to the beach take a nap in the sun, get on bike...... three four kicks, ugh, use the starter, starts up, doesn't ride so well.... breaking up around four grand and backfiring under load like crazy, no power, header pipes are not too hot, but all equal, got spark on all four, figuring carbs or bad gas.... where do I go. and what screw does exactly what on these carbs, there's one pointed up on the outer side of each carb, an 11 or 12 hex on top, and the small flathead with a lock washer on it on top as well.... Was going to pull the plugs to look, but alas, i don't have a socket here, and i just brought all of my tools to Marin earlier today for my new job, was going to ride to work thursday for my first day, guess not now... also, running points, and Dyna 3 ohm coils, have had no trouble with them for almost two years now.

[Brandotheamazing]

wondering if I just got a cra**y tank of gas...

[TrueSpin]

Sounds like a lean condition to me... I'd say check your float heights... Could be a small clog in the fuel line, also. Any sort of small debri anywhere in the fuel system.

[jessezm]

To me, the fact you had to kick it over coupled with the fact you're running Dyna 3 ohm coils points to charging system issues.  The smaller 4's (350-550) do not have an impressive charging system, and those 3 ohm coils draw a lot of power.  My guess is that you ran your battery down on a low rpm around-town ride and your bike is now stumbling under load.  Charge the battery up and see if you temporarily get your bike to run better.   In my opinion, you ought to think about swapping those 3 ohm coils out for the dyna 5 ohm coils.

Also, if you don't understand what the various adjustment points on the carbs do and the theory behind them, I wouldn't go messing around with them!  There's really not much you can do to them without taking them off that's going to make a huge difference, and if it was running right before, my guess is they are not the problem (unless of course, you have a clogged main jet or something, in which case they do need to be broken down for a proper cleaning).

[Brandotheamazing]

I kick it because I like to, the batt is strong enough to start it too. Might be a clog, one of the small rubber hoses between two of the carbs disintigrated, wonder if that'd do it.... ill pull the rack next days I have off.

[jessezm]

whoops, I think I read that backwards...  thought you were loosing battery power.

[chrima]

Check that some funny A$$ didn't switch your spark plug wires on a couple plugs.

Sounds like exactly what happened to me. Ran great when parked. Went to start up and it missed n backfired and ran poorly. Was very hard to get started.

I spent hours going through tune up procedure, cleaning points, timing etc, only seemed to make it worse. Finally I pulled a plug to check that the spark was sparking at the same time that the mark on the ignition plate said it should. Then I found the #4 was firing when the #2-3 plugs should be firing. Hmmm very suspicious. Lets look at my plug wires. #3 and #4 were swapped.

Switched em, boy what a difference. I was overjoyed that I fixed it, upset I spent hours on it.

Oh well, don't have to go through the tune up procedures for a while now

[camelman]

It could be heavily retarded timing.  Might want to check your ignition plate to see if the screws backed out and let the timing plate turn (could happen for points or electronic ignition).

Camelman

[ZanVooden]

Yeah I would check the points plate and the the points themselves. Make sure the gap is correct and maybe even drag a point file across them once or twice.

I run 750's but I did have one occasion where the bike ran great when parked and a couple hours later ran like crap on the way home. It was a really humid day I remember but I spent hours going through the tune up and nothing worked till I drug a point file across the points and it ran like a million bucks. After that I recut a gasket to seal the point cover better.

[camelman]

One other thing, check your condensers.  They can fail instantly like that sometimes, although they usually get better at higher rpm and run roughest as low rpm... when failing/failed.

Camelman

[trueblue]

One other thing, check your condensers.  They can fail instantly like that sometimes, although they usually get better at higher rpm and run roughest as low rpm... when failing/failed.

Camelman

+1 except a bad condensor will cause it to run worse the higher the rpm

[Brandotheamazing]

One set of points had "ungapped" themselves, screws weren't quite tight. oh well, fixed it, I'll ride it tomorrow, had a couple motivation beers before checkin out the bike, but it runs well now and doesn't break up on the center stand.

[camelman]

One other thing, check your condensers.  They can fail instantly like that sometimes, although they usually get better at higher rpm and run roughest as low rpm... when failing/failed.

Camelman

+1 except a bad condensor will cause it to run worse the higher the rpm

That hasn't been my experience, but I definitely haven't seen it all. 

[trueblue]

One other thing, check your condensers.  They can fail instantly like that sometimes, although they usually get better at higher rpm and run roughest as low rpm... when failing/failed.

Camelman

+1 except a bad condensor will cause it to run worse the higher the rpm

That hasn't been my experience, but I definitely haven't seen it all. 

I'm talking from a car point of view here but the principal transfers to bikes, what a condenser does is absorbs the fluctuations in voltage in the primary windings of the coil and the higher the revs the closer together the fluctations become and thus the engine starts to break down at higher revs