1973 Honda CB350 G back fire issue

[IsaiahPannier]

I am helping my friend with his 73 Honda CB 350 G and he is having issues starting it, when we can get it running (10 minutes of kicking) it has issues of backfiring really badly when the headlights are on but less backfiring when the head light is off. Someone previous to him put led lights on it so idk if that has anything to do with it. Maybe the points could be touching? Any help or ideas?

 

[jmcaya]

I was having some backfire problem recently with my 72 cb350. It has that problem occasionally and it clears up after cleaning points, replacing plugs, and charging battery. These bikes run like crap without a full charge.

 

[DrJ]

Did you set the ignition timing?

 

[IsaiahPannier]

I can't even get the cap off where the points are. I have to get the stripped screws out first, then go from there. I figure this will probably be the only issue because we had just changed the spark plugs and battery. I will post once I figure out if that was the issue or not once I get into that cover.

 

[freeskier332]

I also have a 1973 CB350 that has had some backfire problems. Other then fixing all of the electrical which is a good place to start i have found that it is often the sign of a bad Diaphragm. My right cylinder was backfiring, and running odd even with the timing correct, the valves gaped correctly and the battery fully charged. I pulled the Diaphragm out and sure enough there was a tiny hole... I got a new one and the cylinder was running perfectly.

On another note check your fuel system as well.

 

[IsaiahPannier]

Perfect, I will put that on my list to look at. It is the same issue you are describing that happened to you.

 

[freeskier332]

Yea its very similar to what happened to me. I would say so long as you do the stuff on this list you will be good to go.

1.) Gap your Intake and Exhaust to spec
2.) verify that you have fuel flow to both carbs (stupid but bad fuel pressure from a bad petcock = fail)
3.) make sure the floats are set correctly and that your jets are clean
4.) Inspect your Diaphagrams
5.) check your timing and set point gaps to spec
6.) Make sure your plugs are sparking and that they are not crapped up, if they are all sooty they wont work right
7.) check all of your electrical connections so something isnt grounding and fully charge your battery
8.) adjust your cam chain tensioner

If all of that is done you should have a perfectly running bike... that is so long as you have good compression and no air leaks