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Discussion Starter · #1 ·
I have a 1971 CB350 that I am restoring, first it ran great when I got it and one day it stop running great and started running really poorly. Low power when accelerating, choppy and sputtery.

I have not done much since the day that it started doing all that stuff, i start it and tinker a little bit but it is way off.

I just pulled the plugs and the left plug is wet with gas and the right plug is dry and jet black ( carbon )

What is the cause of all this and how can I remedy it? The bike is in some pieces right now as I finish some of the part off, battery box repainted, etc...

I really want to get this thing back to running shape, when I was driving it and it ran really well it was awesome! In the matter of one morning it went from stud to dud! ha. So, yea, it happened quick.

Thanks a ton in advance!
 

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ctots said:
I have a 1971 CB350 that I am restoring, first it ran great when I got it and one day it stop running great and started running really poorly. Low power when accelerating, choppy and sputtery.

I have not done much since the day that it started doing all that stuff, i start it and tinker a little bit but it is way off.

I just pulled the plugs and the left plug is wet with gas and the right plug is dry and jet black ( carbon )

What is the cause of all this and how can I remedy it? The bike is in some pieces right now as I finish some of the part off, battery box repainted, etc...

I really want to get this thing back to running shape, when I was driving it and it ran really well it was awesome! In the matter of one morning it went from stud to dud! ha. So, yea, it happened quick.

Thanks a ton in advance!
The fact that it started running poorly so abruptly is a clue so I wouldn't start playing with the carburetors at this point. That leaves two other areas, compression and ignition.

If it was me I would check to see if you have any spark at the left plug. If the left plug is has spark, you need to check the compression with a compression guage.

Let us know what you come up with and let us know if you're unfamiliar with how to preform any of these tests.
 

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Check your battery first.

Then go to your User Control Panel and add your year/model, location, and real name (hopefully) to your signature....
 

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Welcome to the site ctots!

As MNellis says, first things first when it goes from all to nothing so quickly. Check for spark and then compression. If you don't have a compression tester, you can usually borrow one from your local big box auto parts store (with a healthy deposit just in case you forget to bring it back...haha).

Let us know the results of your tests.

tbpmusic had a couple of downloadable manuals somewhere on this site, but I'm not finding them very easy now. This would be good for you to have.
 

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pantera1 said:
Welcome to the site ctots!

As MNellis says, first things first when it goes from all to nothing so quickly. Check for spark and then compression. If you don't have a compression tester, you can usually borrow one from your local big box auto parts store (with a healthy deposit just in case you forget to bring it back...haha).

Let us know the results of your tests.

tbpmusic had a couple of downloadable manuals somewhere on this site, but I'm not finding them very easy now. This would be good for you to have.
TBPmusic has a great suggestion that I forgot, make sure the battery is fully charged and in good condition. These things don't run well at all with a low battery.
 

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Discussion Starter · #8 ·
I checked the spark this morning after I got the battery back in. No spark on the left side, spark on the right.

Prior to checking this, I started it and it started up, not sure if there was spark at that point, but there sure is no spark on the left now.

What should I do now? Check the coil? What should I be checking for?

Thanks a ton!

Chad
 

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You need a digital multimeter to measure a couple of things. First, set it to ohms to measure the resistance between each wire of each coil to ground (bare metal part of the bike, like the engine fins..) with the key off. I got 5 ohms at each on my bike yesterday. I'm not sure what spec is, but you don't want it to measure zero ohms or it means you have a burned up coil (bad coil.) Also you want there to be some resistance but not too much.

The next check is to turn the key on and test the voltage that is going to each coil. Hook the multi meter to the coil and to ground again and be sure you're getting 12 volts+ to each coil. Mine measured 12.26 volts to each coil with the key turned on.

I had the same problem where the bike wasn't running on the right cylinder even though my coil tested as good. eventually it started working though. The caps on your spark plugs unscrew from the wires. You might want to unscrew them and spray contact cleaner in there and screw them back into place. Be careful not to damage the spark plug wires because you can't replace them at the coil.

To 'check spark' I use a timing light. I hook it up to a car battery and clamp the pickup on my plug wires. This way I can visually inspect the strobe light to see if it stops making spark at higher RPM or whatever. Or I can see if there is intermittent missing of spark. I gave up looking at the spark at the plug (shocked too many times!)

Stolen from the internet:
http://en.allexperts.com/q/Motorcycle-R ... roblem.htm
Electrical Testing Early Honda's

Ignition source Coil
1. With the magneto wiring disconnected, block the breaker points open with a piece of paper such as a business card.
2. Measure the resistance between the ignition source coil wire and ground with a low range ohmmeter. If resistance is about 0.5 ohm, the coil is probably good.
3. If possible, disconnect the ground wire between the ignition coil and the magneto base. Measure insulation resistance between the iron core and the coil. Insulation resistance should be at least 5 Meg ohms.

Condenser
Unless you have a special condenser tester, do this quick test:
Connect the negative lead (-) to the negative terminal of a 6-volt battery, and the positive lead (+) to the positive terminal. Allow the condenser to charge for a few seconds, then quickly disconnect the battery and touch the leads together. If you observe a spark as the leads touch, the condenser is good. Arcing between the breaker points is a common symptom of a defective condenser.

Charging Coil
Measure the resistance from each coil output lead to ground. For most coils, resistance should be in the range of 0.3 to 0.6 ohms. If possible, disconnect the ground wire from each coil, then measure insulation resistance between the coil and ground. Any indication of less than 0.5 Meg ohms means that the coil is shorted. Some magnetos have built-in diodes (rectifiers) for battery charging current. If so, resistance should be very high measured in one direction, and very low in the other (switch leads).

Rectifier
Same as last sentence, high resistance one direction, low the other.

Ignition Coils
1. Measure resistance of between the positive and negative primary terminals (small wires). Resistance should indicate about 5 ohms for most coils of this type. Some have a primary resistance of less than 1 ohm.
2. Measure resistance between either primary terminal, and the secondary high voltage terminal (spark plug wire). Should be between 5K and 11k ohms.
3. Check condition of spark plug cap. Look for cracks, dirt, and defects.
 

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pantera1 said:
MNellis said:
These things donQt rum welll at all with an low battery.
Nice sentence! Rum is the key word. :lol:
That's what I get for replying from my cell phone. :)
 

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Discussion Starter · #12 ·
awesome stuff! thanks all. I have new observations if I may.

First, the spark is back on both sides and I did get it to start and it was running and idling pretty nice, not choppy and not sputtery. The idle was good and then, the green light on the tach started to dim and the bike slowly sputtered out and now it won't start and that green light is off, also the idle came down slow right before it shut off. It will crank over with the electrical ignition, which by the way turns over but I was only able to start it with the kick, previously the electric worked just fine.

The plugs look a bit better, the right one now had a little of gas on it, but then I checked it again and it didn't ( after it ran again) I did run it at like 4000 RPMS for 30 seconds and then cut the engine, the plugs looked ok... I think they should just be replaced because I can't tell if what is on them is from old or new, I did clean them but still

I did check the spark plug caps and made sure there was no cracks, etc... I have also looked over all electrical connections and did find a few loose connections, all this was caught before the bike ran today, and it did run pretty good for about 5 minutes before it went off.

I think it might be electrical, what are symptoms of bad coils? Maybe the battery is shot, It was bought new a few months ago...

I am going to try and test them, get one of the meters... etc. Thanks so much for all the help. Can't wait to sort it out and I feel as though I am getting close and learning.
 

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Discussion Starter · #13 ·
Re: Carb issue? - Update

So, I went over all things over the winter that I did to the bike, one thing that I did was reinstall the right rear turn signal. It was off the bike when I got it. When I un-wired this turn signal and removed it the bike is working fine now. A little rough because I have been messing and turning screws, but power is back, starts right up and both cyclinders are firing nicely.

Weird that this would mess the bike? Anyone have any clues as to why or seen anything like this?

Chad
 

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I don't know a whole lot about these bikes but I do know a fair bit about electricity and I remember hearing that the electrical/charging system on these bikes is iffy at best.

The turn signal could be grounding out or simply displaying a very large resistance. This would put a greater than normal load on the system and could cause weak spark.
 
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