Honda Twins banner
1 - 14 of 14 Posts

·
Registered
Joined
·
9 Posts
Discussion Starter · #1 ·
OK, so I bought a 1969 cb350 about 2 weeks ago. The bike ran perfect when purchased but it now has a few issues. The bike is only running on one cylinder and I cant seem to figure out why. I have limited mechanical experience but with the right direction I am good at trouble shooting. The bike has no side covers and has pod filters installed.

Here is a detailed account of everything that has happened in the last few days. I hope it can help diagnose the problem.

As I said, when I bought the bike it ran great. First week had zero problems. The only issue was the turn signals wouldnt always work, sometimes they would, sometimes they would not. I assumed this was a wire grounding out somewhere and I planned on tracing them all when the weather got better (its been raining alot recently).

One night while out with my girlfriend barhopping, we got caught in a sudden rain storm. Pulled the bike over under some cover and waited it out. Rode to the next stop without any problems, parked the bike, and went inside for an hour. When we were leaving, the bike's electric starter wouldnt turn the bike over, like the battery was dead. Headlight still worked however. I kicked the bike over and it fired up first kick. Pulled out and the bike was bogging down really bad (like it was running on one cylinder). After about a 1/4 of a mile it backfired and started running fine.

It continued to do this for a day or two, untill finally it just started only running on one cylinder. I am assuming it is something in the ignition system, but since I've never gotten into one before I'm not sure where to start. I have to go buy a spark plug socket tomorrow to pull and check the plugs, but not sure what to do after that. I moved the gas tank and tapped around where the spark plug wires are and started the bike and it would backfire out of the right pipe again then stop and continue to only run on one cylinder. I was thinking maybe a lose wire or bad connection. I tightened down all the screws in that area but it did not seem to affect the problem. Also I am not sure how to check points on a bike.

After researching around the internet it seems that it could be the battery is bad, the petcock needs replaced, carbs filled with water, etc. These are all fixes that I've read so far. The petcock does seep a little gas and needs to be fixed/rebuilt I'm assuming but it has been like that since before the problem started. The battery could be bad, but it was a new battery installed by the PO so unless cruising around town under 3500 rpms killed it, which I understand that it can, I doubt it is. It still seems to work the lights just fine when the bike is off, they are not overly dim or anything. It does not have enough juice for the elec start however, so can the battery being really low cause it to run on one cylinder?

Any help anyone can provide would be awesome. If there is any info I can further give about the bike just let me know.

Thanks and sorry for the long post.

Eddie
 

·
Sensei
Joined
·
27,183 Posts
Eddie... the 350's won't run properly with a bad or low battery... Your signal grounding out could have discharged it to this point, and a new battery is not necessarily good....
 

·
Registered
Joined
·
45 Posts
The starter may be a poor/dirty conection or a failing relay(solinoid) or worst still a failing starter. Enough power gets to lights but not the starter. Try cleaning and tightning the battery cables-test. If still a problem try to jump start it or check battery voltage. You can also "hot wire" the relay to test if it's out. You can try a relay by-pass too, but first clean the relay connections and see if that's the bad spot. Also the connection at the starter may need cleaned and or is loose. You can check the starter by jumping directly to the starter. This may or may not relate to your other problem but will at least address the starter issue.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #4 ·
Ok i'll pull the battery and get it tested and charge it to full and see what that does. I'll also pull the plugs and see what they tell me. I guess this could be as simple as just putting a battery tender on it every other day. It would explain why it ran so well then slowly died off i suppose.

I'll pull out my clymer manual tomorrow and check the points and trace all the wires and make sure they have a good connection and are not grounding out. I'll also figure out where the turn signal wires are grounding out, maybe just outright disconnect them and rewire them one by one to ensure a good/clean connection.

The bike has had a little top end noise since i got it. A friend who is sharp with old CBs told me it was minor valve noise and definately not the cam chain. The PO said he adjusted them but again that doesnt mean they were done right so I might need to readjust them as well.

Unfortunately I live in an apartment and had sold all my tools awhile back. I need to buy a few needed tools as well as a tarp or bike cover to keep the bike out of the elements at night.

Thanks again for your help and any other ideas are very welcome.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #5 ·
So i took the battery to the auto parts store today and had it charged and tested. The battery came up fine. Took it home and threw it back in and the battery now turns the electric starter over just fine. So i will be purchasing a battery tender to keep a nice charge on it so small rides around town dont drain the battery.

On to the running one cylinder problem. I pulled the plug on the side that isnt firing and it was completely black. I assumed this was from pulling water up into the carbs that might have got sucked in through the pods after all the rain we've had recently, since the pods are exposed to the elements.

After setting the gap on a new plug and installing it into the bike, i took it for a short trip up the street, less then 1/4 of a mile. The bike ran great, not as good as it did before these problems, but pretty good. I parked the bike and pulled the plug and the brand new plug was black, not as bad as the old one, but still black. It doesnt seem like oil though, more like gas from what i understand.

I'm hoping this is something in the carbs or the petcock. I'm guessing the carbs are either filled with water and need to be pulled, drained, and cleaned and tuned, or the petcock needs rebuilt. The petcock does seep gas and im thinking this could be the culprit. I also noticed when checking if the pipe was heating up on the side that wasnt firing that when the new plug was in it started to get hot but not as quickly as the other side, not sure if that means anything.

Can the float hights being off cause something like this to happen? what about a carb diaphragm being torn?

If anyone can help me further diagnose this I would really appreciate it. Thanks.
 

·
Registered
Joined
·
175 Posts
If the black plug is oily, you're getting oil in the cylinder. If it's dry, fluffy black, your cylinder if firing but is flooding. If it's wet with fuel, the cylinder is flooding and not firing. The plug tip will probably burn briefly if you touch a match to it. Not likely to be water, but if the filter element is wet the cylinder may not be able to draw air through it, resulting in raw fuel from the carb being sucked - without adequate air. Could be float set wrong, could be a particle of dirt in the float valve. Sometimes running the bike with the fuel cock off 'til it stalls then opening the fuel cock will flush out the float valve, but don't count on it. you may have to take it out and clean it or replace it, and check the float height while you're at it. They'll run OK a little low but not at all well if the float level is too high.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #7 ·
I dont think its oily, but I'll have to check again tomorrow to be sure. Its just black, but I didnt really detect any fluffy deposits. It seems carbon fouled and a little wet, but not oily wet.

I'll post a pic of the plugs tomorrow.

It also seems i'll be pulling the carbs for a cleaning. I'm really hoping this is the problem. I think it is, due to the fact the bike was running so well and all of a sudden started developing this issue after riding it through the rain and it sitting out overnight in the rain. I also noticed today a good amount of rust in the inline fuel filter i fitted to the bike. Maybe a piece of rust got through and has caused the float to stick or the float valve.

If the plugs are oily, that means rings right? how expensive of a job is that? Can this just suddenly happen? I mean the bike ran fine for a week or so after i purchased it, no issues at all, then the problem developed. Now if i ride a block the plug fouls. So its not as if the PO threw new plugs in to unload the bike, otherwise it would have fouled the plugs on the 10 mile ride home, let alone the week of driving it every day.

Thanks again for the suggestions. Any further help is always appreciated.
 

·
Sensei
Joined
·
27,183 Posts
Here is what I BELIEVE could be wrong..... One of the point wires is grounding out its coil.... This could be from a fray or "nick" where it comes out of the housing.... When you rode in the rain, the water "helped" assure this little bared section of wire made good ground contact and effectively shut down one coil.... This accounts for the black, wet plug as well... wet (gas fouled) when the point wire is shorted, and blackened from the (rare) firing in flooded condition when it's not shorted... Water getting behind (into) the point cover can also cause this......
This isn't the only possibility, just one of them....
Rain water can saturate the air cleaner and cut off some/most of the air supply causing the mixture to richen excessively....
Wet HT leads from the coil can short to a convienient ground rather than spark the plug... Etc, etc...
Then, there's the rust you mentioned.....
You will have to eliminate each possibility one at a time until you find the exact problem...then fix it.....Just offering some of the possibilities...
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #9 ·
Thanks. These all help greatly. I'll check the points tomorrow as well as all wires leading to the coil, and make sure everything has a clean dry connection. If this doesnt eliminate the problem I will then pull the carbs and start cleaning.

If the rain would let up my motorcycling life would become much easier.

Thanks again.




Eddie
 

·
Registered
Joined
·
45 Posts
Your problem to me sounds like carbon fouling of the plug-over rich fuel mix. This will cause the cylinder to run cool untill it fouls compleatly out. Then you'll have a gas fouled plug. Disconect the air filter, look inside the carb opening and check to see if the choke is hanging. Put in a clean plug. Then start it and run with the filter unconected. Soon as it's warmed a bit give it some gas about 5,000 rpms worth for 60 seconds. While holding 5,000 rpm cut the motor off and check the plug-if it's black but not oily it's carb tune up time-if it's clean reconect the filter and run the same test again-if it's black now it's new filter time.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #11 ·
CB200 said:
Your problem to me sounds like carbon fouling of the plug-over rich fuel mix. This will cause the cylinder to run cool untill it fouls compleatly out. Then you'll have a gas fouled plug. Disconect the air filter, look inside the carb opening and check to see if the choke is hanging. Put in a clean plug. Then start it and run with the filter unconected. Soon as it's warmed a bit give it some gas about 5,000 rpms worth for 60 seconds. While holding 5,000 rpm cut the motor off and check the plug-if it's black but not oily it's carb tune up time-if it's clean reconect the filter and run the same test again-if it's black now it's new filter time.
awesome. Just got home from work so I will try this in a few minutes.

Thank you everyone for the input. I'm pretty sure I will get this diagnosed soon.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #12 ·
Ok so heres the update. I cleaned the points and made sure there were no wires grounding out. Immediately I noticed one of the retaining screws for the right side was missing. I see this as being a problem lol. I cleaned the points, set them as best I could, and presto the right side pipe was heating up and everything seemed fine.

After running it around the block there was still some carbon fouling on the plug, i figured it was time to tune the carbs. I attempted to tune them according to my Clymer manual and everything seemed fine until I tried to disconnect the left plug and run it on the right cylinder only. Bike wouldnt start. I'm guessing it still isnt getting the best contact.

Where I'm at now is finding a screw that fits the retaining screw hole for the points. Filing them down and getting them set right (or replacing them), then tuning the carbs, set timing, etc. This should fix me up. Also I noticed the carbs need to be sync'd. When I'm throttling down the bike isnt revving down as quick as it should, almost like its sticking, but it is not.

I did get the bike running pretty amazing though while tinkering today. It holds at any RPM very smooth, no backfiring or bogging down. Just the issue with it seeming to rev high when coming off the throttle.

I'm either going to try and find some new points and do everything myself, or take it to a shop to have it professionally done. I'd rather do it myself but my lack of experience might win out.


On a side note, does anyone know where I can get new points for the bike? Ebay? or is there a place to buy new? I also need a petcock rebuild kit.
 

·
Premium Member
Joined
·
10,203 Posts
Tuneup kits show up on e-bay pretty regularly. Haven't really paid much attention to how they're priced but at least they are available.
 

·
Sensei
Joined
·
27,183 Posts
First thing.... Replace the missing screw and recheck/reset timing..... Then we'll see what's happening.......
 
1 - 14 of 14 Posts
Top