Author Topic: Confirming a diagnosis (Read 2553 times)

Genesis322 · « **on:** June 01, 2011, 06:47:21 PM »

In trying to iron out all the bugs on my recently acquired 76 CB550F and while checking the plugs noticed 2 and 3 were clean as a whistle. When I yanked the the wire on 2 and 3 while the bike was running nothing changed. Turns out neither 2 or 3 are firing at all. I get a very weak spark on those two plugs. I'm thinking bad coil? Anyone want to confirm or deny before I hit the net and make an order?

Bankerdanny · « **Reply #1 on:** June 01, 2011, 06:49:24 PM »

A reasonable hypothesis. Have you tried cleaning all the connections at the points and coils first just to confirm that it isn't simply bad connections?

BobbyR · « **Reply #2 on:** June 01, 2011, 07:01:38 PM »

Also take off the caps and clip off the tip of each wire, get some fresher copper for the cap to bite into.

dave500 · « **Reply #3 on:** June 02, 2011, 02:20:57 AM »

if you have a multi meter check the caps resistance,these coils rarely go bad id be going over the points and condensors first and checking and cleaning any connections,was the bike running when you bought it?

Genesis322 · « **Reply #4 on:** June 02, 2011, 03:01:48 AM »

I sanded the points, the contacts were a little dirty but not bad.

The bike started when i bought it but had been sitting for 5 years. I cleaned the carbs and did some minor "wake up" work to it and have tooled around town for about 30 miles trying to work fuel treatment through the system. It still runs rough (apart from the 2 cylinder thing) which I'm taking to mean I need to balance or perhaps go ahead and rebuild the carbs.

I'll take the fresh copper advice and no I hadn't checked the connection at the coil. Thanks for the advice, it's my first bike and first post on the forum and already I can see it's going to be a lifesaver!

Toxic · « **Reply #5 on:** June 02, 2011, 03:57:41 AM »

Start with the cheap stuff first, do you have power at the 2-3 points, if yes then start following the points wire backwards and make sure you are getting power at the coil.
If you have power at the coil for 2-3, switch the wires and see if 1-4 are now dead and that will tell you if your coil is kaput.

Spanner 1 · « **Reply #6 on:** June 02, 2011, 05:23:32 AM »

Along with the plug-cap advise, I think it's time to clean your carbs, esp. your slow jets ( lots of carb cleaning advise here, just be sure to do it all! ). Cyl. 2+3 plugs should be soaking wet if not firing and the bike has been run on 2 cyls not 'clean as a whistle'.........

Bankerdanny · « **Reply #7 on:** June 02, 2011, 06:20:09 AM »

And when I say clean the points, that means all the various connections, not just the points themselves.

My misfiring issues were due to the nut on the points that holds down the blue wire from the condenser being loose

Genesis322 · « **Reply #8 on:** June 02, 2011, 07:32:18 AM »

Great stuff! I'll do the switch when I get home. When I said clean as a whistle I meant the contacts weren't black (rich) like the outer two. I'm gonna see if I can confirm all the electrical issues before I take the carbs off again, but it's in the schedule.

BobbyR · « **Reply #9 on:** June 02, 2011, 08:32:06 AM »

Quote from: Spanner 1 on June 02, 2011, 05:23:32 AM

Along with the plug-cap advise, I think it's time to clean your carbs, esp. your slow jets ( lots of carb cleaning advise here, just be sure to do it all! ). Cyl. 2+3 plugs should be soaking wet if not firing and the bike has been run on 2 cyls not 'clean as a whistle'.........

+1
That is a a major symptom, good ctach. It is possible on your test ride your carb cleaner loosened up some crap and plugged up one of the circuits. I have tried all the quick fixes and it took more time and effort for little result than tearing them.down.

Genesis322 · « **Reply #10 on:** June 02, 2011, 10:18:46 AM »

On a related note on test drives recently I've run down the battery. I think I drained it by leaving it powered on while tinkering (20 mins) but I threw a short charge on it (30 mins at 10amps) and then rode it home for 5 miles and then it died again. Do you need to run it longer to charge on the bike or could there be an issue with the charging system?

BobbyR · « **Reply #11 on:** June 02, 2011, 11:09:40 AM »

I am not sure what bike, but generally the charging systems do nothing at idle. While you were idling the battery is actually running everthing. You can verify what voltage output is being sent to the battery at any given RPM.

Genesis322 · « **Reply #12 on:** June 02, 2011, 05:00:01 PM »

Well that is the thing, I ran it with a meter on and idled around 12 and revving took it up 2-3 as you would expect so it seems like all is well. I guess I'm not accustomed to running down a battery that soon as it is my first bike.

Everything around the points looks pretty tidy and new. We did mess a bit with plate position just to see if timing was an issue before we noticed the two cylinders not running but that's all tightened down again.

For Toxic's suggestion I didn't see an obvious way to switch the wires on the coil so I'm gonna do some digging to figure that out.

I'm gonna put some carb rebuilds on order just for good measure, after reading suggestions I don't think I did a complete job of that the first time.

Thanks again, great forum with really helpful people.

BobbyR · « **Reply #13 on:** June 02, 2011, 05:26:50 PM »

Quote from: Genesis322 on June 02, 2011, 05:00:01 PM

Well that is the thing, I ran it with a meter on and idled around 12 and revving took it up 2-3 as you would expect so it seems like all is well. I guess I'm not accustomed to running down a battery that soon as it is my first bike.

Everything around the points looks pretty tidy and new. We did mess a bit with plate position just to see if timing was an issue before we noticed the two cylinders not running but that's all tightened down again.

For Toxic's suggestion I didn't see an obvious way to switch the wires on the coil so I'm gonna do some digging to figure that out.

I'm gonna put some carb rebuilds on order just for good measure, after reading suggestions I don't think I did a complete job of that the first time.

Thanks again, great forum with really helpful people.

No you don;t understand you swap the wires at the plugs, if 2-3 come to life and 1-4 die it is ignition. If not, it would be fuel related. These motors use waste spark so 1-4 and 2-3 fire at the same time. So put 1-4 on 2-3 and 2-3 on 1-4.

TwoTired · « **Reply #14 on:** June 02, 2011, 05:50:17 PM »

The 550 has a 12 amp hour battery.

You aren't supposed to charge it faster than a 1.2 amp rate. At that rate, it will take 10-12 hours to fully charge it from dead.
10 amps heats the battery up pretty good and 30 minute really only put about 1/3 of the storage capacity back in. You must put back 120% of what is removed, as the battery is not 100% efficient. (It's a chemical device that uses or makes electricity during the chemical reaction.)
Draining a battery that far (dead), damages it a little (or a lot) each time that occurs. So, your battery changes into a 10 AH battery then an 8AH battery, and so on until it can't last long enough to be useful anymore. Usually one of the six cells quits before the others leaving you with a 10V 4 AH battery.

The bike alternator charges at a 1-1.5 amp rate, IF you rev it beyond 3K. The electric starter draws about 25-30 AMPs. The rest of the (stock) bike draws about 10 amps with lights on. (Few of these bikes are still stock.)

You should replace the points you just sanded. The grit left behind in the soft contact metal, shortens point life to about 1/3. That's why they made point files.

Cheers,

Genesis322 · « **Reply #15 on:** June 03, 2011, 04:20:06 AM »

Thanks again. I switched the wires at the plug and nada, I didn't know you could do that and have them fire correctly so that is great to know. Looks like I'm taking out the carb again

I really appreciate the battery info, I just tried to throw enough charge to get home but thought it would charge faster on the bike. The numbers you cited really help me understand the issues I was causing myself.

Thanks for helping out a guy trying to get into this stuff for the first time.

BobbyR · « **Reply #16 on:** June 03, 2011, 05:47:54 AM »

We are all guys who just got into this stuff. That is what this place is for.

TwoTired · « **Reply #17 on:** June 03, 2011, 11:42:36 AM »

Quote from: Genesis322 on June 03, 2011, 04:20:06 AM

I switched the wires at the plug and nada, I didn't know you could do that and have them fire correctly so that is great to know.

Switching wires allows testing the components for function. The engine won't run that way. Some tests/experiments are used for fault isolation, and elimination of known good components as a suspect fault candidates.

Cheers,

Genesis322 · « **Reply #18 on:** June 03, 2011, 12:32:41 PM »

Thanks TwoTired, I get the concept now. I was wondering how that would work but it makes sense now. I'm going to clean out the carbs again anyway now that I see all the suggestions on how to do it posted on the forums.

BobbyR · « **Reply #19 on:** June 04, 2011, 07:44:22 AM »

The thing you have to keep in mind with these old bikes is that you cannot always transfer what you know about the modern automobiles to them. I think you have leaned a bit so far.

When you work on the carbs, take your time. I tried every shortcut I could think of and none of them worked. There is no miracle in a can. It takes dis assembly and manual cleaning of some passages. Once you have them right, Seafoam and Techtron are wonderful for maintaining things.

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Author Topic: Confirming a diagnosis (Read 2553 times)