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Discussion Starter · #1 ·
Bought the bike running but not well. It was hard to start and once it warmed up it ran poorly unless you maintained 3500 rpm. I rode it a few times thinking things would smooth out because the guy I bought it from said it had been sitting for a couple of years. I was riding it one day and it just shut down, thinking that I was out of gas I pulled into a station, filled the tank and got it running again. Once home I parked it and a few hours later I tried to start it up but it wouldn't idle and even in the higher revs it misfired. Now the two middle cylinders wont fire. I got the carbs cleaned, replaced a float spring and reinstalled them. No change in the problem, still wont fire on 2 and 3. The plan is to check the compression, readjust the valves, check the timing and the points.
I was thinking about installing the Dyna S electronic ignition module and dispense with the points altogether but money is tight and anyway I don't think the first answer is to throw money at problems hoping they will just go away.
Considering that the cylinders in question are on separate coils it seem unlikely that the coils could be the problem. If anyone has experienced this and has advice it would be appreciated.
 

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Considering that the cylinders in question are on separate coils it seem unlikely that the coils could be the problem. If anyone has experienced this and has advice it would be appreciated.
i would recheck, usually its 1-4/, 2-3 with 4 cyl 4 strokes, why not take it to a local shop? what is a 550pdx? should be a k or a f
 

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Discussion Starter · #3 ·
i would recheck, usually its 1-4/, 2-3 with 4 cyl 4 strokes, why not take it to a local shop? what is a 550pdx? should be a k or a f
sorry, I used 78cb550pdx as my username, my bike is a 1978 cb550k. And regarding the firing order I made a foolish assumption that it was 1-2 and 3-4. Thank you for the info. The reason that I don't want to take it to a shop is that as a rider I should be able to maintain it myself. I will check the coil and I'll get back to you with the results. I am also going to recheck the pilot jets.
 

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Discussion Starter · #4 ·
sorry, I used 78cb550pdx as my username, my bike is a 1978 cb550k. And regarding the firing order I made a foolish assumption that it was 1-2 and 3-4. Thank you for the info. The reason that I don't want to take it to a shop is that as a rider I should be able to maintain it myself. I will check the coil and I'll get back to you with the results. I am also going to recheck the pilot jets.
ps. pdx is for Portland Oregon.
 

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Bought the bike running but not well. It was hard to start and once it warmed up it ran poorly unless you maintained 3500 rpm. I rode it a few times thinking things would smooth out because the guy I bought it from said it had been sitting for a couple of years. I was riding it one day and it just shut down, thinking that I was out of gas I pulled into a station, filled the tank and got it running again. Once home I parked it and a few hours later I tried to start it up but it wouldn't idle and even in the higher revs it misfired. Now the two middle cylinders wont fire. I got the carbs cleaned, replaced a float spring and reinstalled them. No change in the problem, still wont fire on 2 and 3. The plan is to check the compression, readjust the valves, check the timing and the points.
I was thinking about installing the Dyna S electronic ignition module and dispense with the points altogether but money is tight and anyway I don't think the first answer is to throw money at problems hoping they will just go away.
Considering that the cylinders in question are on separate coils it seem unlikely that the coils could be the problem. If anyone has experienced this and has advice it would be appreciated.
Take a look again at Tinsnips post his idea is simple and will answer a lot of questions. Also remember just because you cleaned the carbs if there's crap in the tank you most likely would reinfect the carburetors if you just added gas. Just adding fuel often just stirs the grunge up lets the thing run for a bit,,,, then the crap settles back down around the petcock and the problems comes back. Also make sure all your vacuum lines are connected and are in good shape.
I would also make the thing run right before I spent money on an ignition up-grade. Electronic ignitions are the way to go but use that as a way to make your motorbike run better not a way to just make it run.

Rich
 

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Discussion Starter · #8 ·
Take a look again at Tinsnips post his idea is simple and will answer a lot of questions. Also remember just because you cleaned the carbs if there's crap in the tank you most likely would reinfect the carburetors if you just added gas. Just adding fuel often just stirs the grunge up lets the thing run for a bit,,,, then the crap settles back down around the petcock and the problems comes back. Also make sure all your vacuum lines are connected and are in good shape.
I would also make the thing run right before I spent money on an ignition up-grade. Electronic ignitions are the way to go but use that as a way to make your motorbike run better not a way to just make it run.

Rich
Thank you for the insight.
 

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If there was confusion on the firing order make sure you don't just have a couple of leads crossed.
Points or condenser would be my guess, there is an element of luck in setting points if you don't use a meter to check for zero resistance when the points close. Points go hand in hand with a condenser and the condenser has a high failure rate when they get old or rusty. Typical fix was to replace the condenser and service the points because the condenser is relatively cheap and the points considerably more expensive.
... I suspect when you bought the bike it was running on 3 cylinders. You should be looking for all of the headers to get real hot real fast, don't burn yourself checking.
 

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One coil fires 1&4 and the other fires 2&3. The problem could be points wide open or closed or fouled, or a broken connection. Or a coil may have died. More likely to be fouled plugs or dirty points but could also be a dead condensor. Dyna ignition is a cheap and useful upgrade but see where the problem lies first.

The coils are double ended and if one plug is fouled it is likely that they other plug on that coil will also not fire.

I would pull all plugs and clean or replace them. Then clean and set the points and then spin the motor over and see if all 4 plugs fire by putting clean/new plugs in each plug cap and set them against the head or barrels so they ground and press the starter button. All 4 should spark.

If/when the ignition checks out, then clean the carbs and fuel filters including the one in the fuel tap.
 

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Discussion Starter · #11 ·
One coil fires 1&4 and the other fires 2&3. The problem could be points wide open or closed or fouled, or a broken connection. Or a coil may have died. More likely to be fouled plugs or dirty points but could also be a dead condensor. Dyna ignition is a cheap and useful upgrade but see where the problem lies first.

The coils are double ended and if one plug is fouled it is likely that they other plug on that coil will also not fire.

I would pull all plugs and clean or replace them. Then clean and set the points and then spin the motor over and see if all 4 plugs fire by putting clean/new plugs in each plug cap and set them against the head or barrels so they ground and press the starter button. All 4 should spark.

If/when the ignition checks out, then clean the carbs and fuel filters including the one in the fuel tap.
I replaced the plugs, checked the points (they are new and not pitted at all) and they open and close as they should. I checked the spark on all the plugs and 2/3 seem to have far less spark than 1/4 so I will install the new coil today and see what happens. Thank you all for helping me think this through.
 

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Discussion Starter · #12 ·
I replaced the plugs, checked the points (they are new and not pitted at all) and they open and close as they should. I checked the spark on all the plugs and 2/3 seem to have far less spark than 1/4 so I will install the new coil today and see what happens. Thank you all for helping me think this through.
So this is what I found. A questionable solder job involving the black and white striped wires coming from the harness and my ignition? The coil I bought has a slightly different setup. The way it is wired up now is that the wires (black and white) are combined into one connection. Question, is that the configuration it is supposed to be in? Or Is that the problem?
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Well I screwed that up, sorry about the double image.
78,
First you need to know what wire is the ground in YOUR wire harness. " Simple way without extra tools" You will need 1. a test light ($5 @ Auotzone, one length of wire; , and a test battery (the one that was in your motorbike). Take one wire and run it from the ground side of the battery to the frame of your bike ... secure. Now take the alligator clip on the test light and hook it to the + side of the battery. By touching the ends of the two wires you are running to the coil the one that lights up is the one that goes to the - (ground) side of the coil and is the ground to the coil. Doing it this way will make sure you have a solid ground and will avoid any other thing within the harness. Solid black or brown is usually the ground but not always. The second wire will be one color for one of the coils and another color for the other coil. I would then make sure that the other side of the coils are getting power when the switch is on.
By the way it was suggested that you swap coil leads and see if that changes which cylinders are not firing. did you ? This will at least tell you if it is the coils and not a wiring problem. RULE always make sure your grounds are good, then that you have power and after that everything else. Half the time it's a bad ground...'cause old motorbikes are,,,,,,,,,,,,,,,, well old motorbikes.
Cheers
 

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I replaced the plugs, checked the points (they are new and not pitted at all) and they open and close as they should....
You can use an ohm meter to confirm the ignition points have zero resistance :geek:
and for the coil only a relatively low resistance, as per your service manual
 

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That's a start. BTW, power goes from battery to main switch to run-off switch to coils to ground through the points, so the power from the switch goes to the + side of a coil and the points connect to the -ve side.

Now to find out why it runs rough
 
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