1973 CB350G Problems! Please Help!

R

RobTheCafeNewb

New Member
Ok, so I am having a very strange series of problems with my 1973 CB350. Its a long story so I will try to make it as simple as possible. First some background on the bike:
I bought the bike not running a few months ago. Changed the oil, gas and charged the battery. It started after the 3rd kick. It would idle just fine at around 1500-2000 and would rev to redline, so I rode it around the yard and it would bog down at around 5k rpm. So I decided to start working on it. Heres what I have done:
-Cleaned the carbs
-New fuel lines
-Petcock rebuilt
-New plugs
-Other stuff that has nothing to do with it starting/running.
After I did all this, the bike would start up and run but only on one cylinder (the right side). So I installed new points and condenser. The bike still wouldn't run on both cylinders and the left side point would not spark, so we did some troubleshooting and decided that it was the coil. It had some of its insides seeping out around the end seam and had a burnt smell to it. So it was pretty much fried. Someone brought me a coil from a suzuki of some kind and we installed that on the bike since it looks almost identical and fits perfectly. Now both points are firing like they should be, but the bike wont start or run worth a damn.
It will act like its going to start and sometimes it will, but it will only run at around 1000 rpm and thats with the throttle wide open.

Does anyone have any thoughts or suggestions as to what might be the problem?
Its driving me nuts, so any help would be great!
 
You only need three things to get an engine to run:

1.) The correct fuel/air mixture. After kicking the bike over many times (10+) without a start, are the plugs both wet with fuel? They should be. If they're completely soaked, you'll not be likely to get a spark from them until they dry off.

2.) Compression. You can get a bike to run with as little at 80 PSI, but you're going to want twice that for it to run well. Get a compression checker. Cold readings should be at least 120 and better to see closer to 150. A 350 engine that's warmed up and recently run should be 165 PSI or better.

3.) Strong spark at the correct time. You say you have spark, but is it good? It should be fat and white or (even better) blue in color. Pull each plug and hold it against some bare metal on the bike. Have a friend kick it over a few times while you inspect it. If spark is strong, double-check the timing. The best spark in the world won't ignite the mixture if it's too late to too early.
 
Sonrier-
1. I have gone through this exact scenario many times. I would kick it repeatedly and then pull the plugs. They would almost always be wet, so I would bead blast them and then blow them off.

2. I have done a cold compression test a few times and get readings of about 156 give or take a few for each cylinder.

3. The spark coming from the points is bright blue in color, I have tested the plugs in the way you describe and have gotten a strong spark from them as well.

So that leaves the timing, I will check it tomorrow and make sure that is where it needs to be.

Thanks for the info!
 
What did you mean when you said big blue spark at the points? There shouldn't be much of a spark at the points when it's running. That's what condensers are there to restrain.
 
I removed the carbs today and gave them a looking over again and I couldnt find anything wrong. I took an air blower and blew into the passage to test the diaphragms, they seem to be working fine. I took off the rubbe intake boots and they seem fine as well, one has some slight surface cracking but that shouldnt be enough to keep it from starting or running. I'm almost certain that its a carb problem.
The current state is that it will start every now and then and run for a few seconds at very low rpm with the throttle wide open, I'm at a complete loss of ideas with this.
 
It sounds like the float level is wrong, the jets may be wrong and you may have screwed the diaphragms?
You have taken the vacuum chamber tops off and checked there are no holes and tears? (you need to stretch them VERY slightly)
Blue spark isn't oo uncommon at points, it shows you getting power there.
When you say you cleaned the carbs, how exactly did you clean hem (remove all jets, bits of brass, tops , slides, needle etc?)
 
I've looked at the diaphragms and there are no obvious holes or tears, but I havent tried to stretch them for fear of ripping them myself! I cleaned them by removing everything (jets, floats, needle, slide and anything else I could remove) soaking them in carb cleaner and scrubbing the inside with a wire brush. I used wire to clean the jets. I dont know what size the jets are, but I havent changed them and when i first got the bike it would start fine with them. I haven't checked the float level but I know there is fuel in the bowl because I can open the drain screw and fuel runs out.
 
Diaphragms don't need much to check, you can just run your finger tip under them to see tears, hold up to light to see pinholes
Plugs wont be fouling if fuel levels are correct.
They may get 'wet' but only after you've kicked it multiple times.
If your using the electric foot, check battery voltage while trying to start it
The pilot jets are only about fifteen thou diameter, steel wire can enlarge them pretty easy
 
It doesn't seem to make a difference if I kick it or use the electric start, and the plugs are usually wet after I crank or kick it a bunch, so I clean them up and put them back in. I never had to force the wire in to clean the jets, I was using pretty small gauge wire. Would an air leak or bad timing be enough to cause it not to start? I checked the intake boots and one has some cracking on the outside that doesnt appear to go all the way through. I haven't checked the timing either, I have to borrow a light from someone.
 
You can do a static check on ignition timing, just turn ignition on and turn crank with a 14mm socket (use a breaker bar and remove plugs put them back in caps and ground to engine)
You should be able to see and hear spark at points check timing mark lines up on each cylinder.
slight cracking in carb boots won't matter if it isnt leaking, although wet plugs still sound like fuel level is too high
 
Ok so update time: It's still fucked up.
I checked the timing today and it was WAY off. I set the timing and gaped the points and plugs to spec and made sure I was getting fire, which I am.
I also adjusted the valves. The bike is still starting every now and then and barely running on full throttle. I tore into the carbs and did an extremely thorough cleaning. No clogged jets or stopped up passages that I could find. I blew compressed air into the vacuum passage and the diaphragm slide is working fine on both carbs. I put the carbs back on and there was no change. The funny thing is that the plugs will get wet after I crank on it multiple times and I am getting fire, so why wont the damn thing run right?

Do any of you guys have thoughts on this? Its giving me a headache!
 
How old is the gas?
Are you sure you got everything out of the carbs for cleaning? (I've seen it happen where pilot jets were not removed, just the plugs over them)
Are you certain timing is correct?
 
The gas is brand new, I removed everything from the carbs that could be removed without pressing or punching it out. The parts I could not remove were cleaned with wire and checked for blockage. Besides, the plugs are getting wet when I crank it multiple times, so I am getting fuel.
As for the timing, I like to think it is correct, I had someone there with me who has set the timing on many old bikes in the past and I think he would have said something if I did it wrong (hopefully) lol
 
Really, the only thing left is float height/fuel level?
Have you tried filling carbs then turning fuel OFF?
It sometimes works if they are flooding
 
I dont think flooding is the problem, because sometimes it does start. The problem is that when it finally does start, it only runs with full throttle at very low rpm. My friend who's helping me thinks it is a vacuum leak, probably around the intake boots. I would try squirting carb cleaner and seeing if it raised the idle, but it wont run long enough for that! So the plan is the seal up the cracks in the intake boot with silicone and see if that makes a difference.
 
If you had air leaks, the extra rich condition would be compensated.
If its flooding and float level is correct, you have either enlarged the jets (a lot) or they are mixed up and you have air jets in fuel jet holes or something similar.
Hunting at full throttle sound real rich, you are operating choke correctly?
 
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