[skeletor508]

Hey guys I've been messing around with my '73 CB350 for a while now and every time I more a little forward with getting the bike in running condition I seem to find a new problem. I will give the story of the this never ending battle.

Bought this CB350 about 2 years ago, didn't run when I bought it. Turned out that one of the points wires wasn't connected and were pretty messed up on the contacts. At that point I replace the point, condenser and ran a new wire for the points wire that wasn't connected.

I bought new carburetor floats, and all the stock jetting figured I would just replace them. When I removed the old jets they were all the same sizing that I was putting back in, also checked them against what stock jetting should be. So I am figuring I am good at the carbs.

About two weeks ago the bike seemed to be running ok, it didn't like to get throttle fast and would bog down but it would idle. So I got insurance on the bike and took it to a big parking lot by my house to test ride. Started right up, but one I put it in 1st and got the clutch about 75% out it would bog down and die. When I was loading it into my truck I found out the left exhaust was cold as ice but the right was hot. Brought it back to the house looked like my problem was the carburetor from sitting the needle got stuck and would not let fuel in. After I fixed this the bike didn't want to run and would backfire so I checked everything, I set static timing again, cleaned the carbs, checked spark.

This is when everything started to get worse.

I then thought I was having a fuel issue as from the petcock I was only getting fuel to the right carb. Looked it up and this seems common, and is what the petcock should be doing.

I want to say my problem is a timing issue as when I pull the spark plugs out they are wet with gas and I have spark. But static timing should to be set (how I did the timing was with a test light, coming up on the compression stroke for each cylinder lining it up with fire mark and getting the light to just come on), I was thinking I might have messed up the wiring to the coils so I am attaching a picture of what I have. (From what I found yellow wire is the left points and the gray wire is the right points, connected the yellow wire to the yellow on the condenser and the gray new wire to the blue wire on the condenser, I know the left coil is after market and the right is stock) I even tried to spray starting fluid in the combustion chamber and try to start it and doesn't even want to do that, just backfires after a while. Also did a leak-down test and while I'm not great on compression I still have it in the good marking.

Willing to try anything at this point, figuring if I can't get the bike running I might bring it to someone. Usually never bring my projects to other people but I don't know if I have a choice.

 

[76TWIN]

Have you tested your ignition coils yet? If you swap the coils, does the backfiring change side as well? If so then it's the coil

 

[skeletor508]

Have you tested your ignition coils yet? If you swap the coils, does the backfiring change side as well? If so then it's the coil

I did swap them, when the bike was only running on one cylinder that was my first thought

 

[outobie]

what is your compression? (a leak down test doesn't give compression it yields a percentage)
have you adjusted your valves?

are you getting spark to both spark plugs?

the wiring I can see on the grey wire which presumably is for your left (front point) has exposed wire showing where it connects to the triple terminal by the coil...if your wiring at the points end also has exposed wires it's likely shorting out against the points cover or engine.

is your static timing exactly on the marks?

have you tested dynamic timing to make sure your advancer is functioning properly?

Is your battery fully charged?

 

[skeletor508]

what is your compression? (a leak down test doesn't give compression it yields a percentage)
have you adjusted your valves?

are you getting spark to both spark plugs?

the wiring I can see on the grey wire which presumably is for your left (front point) has exposed wire showing where it connects to the triple terminal by the coil...if your wiring at the points end also has exposed wires it's likely shorting out against the points cover or engine.

is your static timing exactly on the marks?

have you tested dynamic timing to make sure your advancer is functioning properly?

Is your battery fully charged?

I can do a compression test when I get home, but I think I need it warm to get a total accurate reading. I'll cold test tho and see if both cylinders are close. I am getting spark at both plugs, I can redo that connection at that connection and see if it helps. I think the grey wire is for my right coil, I have yellow from the points to the left. Should it be switched? The static timing is right on the fire mark, I do have a timing light but I can't get the bike to even start. Wish I did the compression and dynamic timing when it sort of ran.

 

[skeletor508]

what is your compression? (a leak down test doesn't give compression it yields a percentage)
have you adjusted your valves?

are you getting spark to both spark plugs?

the wiring I can see on the grey wire which presumably is for your left (front point) has exposed wire showing where it connects to the triple terminal by the coil...if your wiring at the points end also has exposed wires it's likely shorting out against the points cover or engine.

is your static timing exactly on the marks?

have you tested dynamic timing to make sure your advancer is functioning properly?

Is your battery fully charged?

Battery is brand new, I even put it on the tender every night

 

[skeletor508]

Keep forgetting things, but lashing/valve clearance is right on spec

 

[outobie]

a cold compression test should only be a few lbs different from hot...cold it should still be greater than 150 PSI and even on both sides.

yes pay attention to your new points wire...a short there would prevent firing. try starting with the points cover off the bike.

if you are timed correctly and getting spark at the plug it's very likely a short.

when you installed your points wire you didn't happen to take the advancer apart did you? and install the points cam 180 degrees out?

get it idling again then do a dynamic timing test taching it up to 4000 RPM and back to check your advancer is functioning properly.

 

[skeletor508]

a cold compression test should only be a few lbs different from hot...cold it should still be greater than 150 PSI and even on both sides.

yes pay attention to your new points wire...a short there would prevent firing. try starting with the points cover off the bike.

if you are timed correctly and getting spark at the plug it's very likely a short.

when you installed your points wire you didn't happen to take the advancer apart did you? and install the points cam 180 degrees out?

get it idling again then do a dynamic timing test taching it up to 4000 RPM and back to check your advancer is functioning properly.

Will do, I never touched the advancer when I did the points so I should be good there. But just in case the guy before me did how would I know if it is installed 180 degrees out?

Just throwing this out there is it possible that the cam chain got thrown off a tooth or two? I did set the tension for it but I something tells me this is something with timing.

 

[skeletor508]

Ended up being the intake valves were not in spec, once I adjusted them bike runs perfect

 

[vietbac77]

Hey guys I've been messing around with my '73 CB350 for a while now and every time I more a little forward with getting the bike in running condition I seem to find a new problem. I will give the story of the this never ending battle.

Bought this CB350 about 2 years ago, didn't run when I bought it. Turned out that one of the points wires wasn't connected and were pretty messed up on the contacts. At that point I replace the point, condenser and ran a new wire for the points wire that wasn't connected.

I bought new carburetor floats, and all the stock jetting figured I would just replace them. When I removed the old jets they were all the same sizing that I was putting back in, also checked them against what stock jetting should be. So I am figuring I am good at the carbs.

About two weeks ago the bike seemed to be running ok, it didn't like to get throttle fast and would bog down but it would idle. So I got insurance on the bike and took it to a big parking lot by my house to test ride. Started right up, but one I put it in 1st and got the clutch about 75% out it would bog down and die. When I was loading it into my truck I found out the left exhaust was cold as ice but the right was hot. Brought it back to the house looked like my problem was the carburetor from sitting the needle got stuck and would not let fuel in. After I fixed this the bike didn't want to run and would backfire so I checked everything, I set static timing again, cleaned the carbs, checked spark.

This is when everything started to get worse.

I then thought I was having a fuel issue as from the petcock I was only getting fuel to the right carb. Looked it up and this seems common, and is what the petcock should be doing.

I want to say my problem is a timing issue as when I pull the spark plugs out they are wet with gas and I have spark. But static timing should to be set (how I did the timing was with a test light, coming up on the compression stroke for each cylinder lining it up with fire mark and getting the light to just come on), I was thinking I might have messed up the wiring to the coils so I am attaching a picture of what I have. (From what I found yellow wire is the left points and the gray wire is the right points, connected the yellow wire to the yellow on the condenser and the gray new wire to the blue wire on the condenser, I know the left coil is after market and the right is stock) I even tried to spray starting fluid in the combustion chamber and try to start it and doesn't even want to do that, just backfires after a while. Also did a leak-down test and while I'm not great on compression I still have it in the good marking.

View attachment 167577

Willing to try anything at this point, figuring if I can't get the bike running I might bring it to someone. Usually never bring my projects to other people but I don't know if I have a choice.

I have the same issue. What I found out was the ignition timing is too retard and the condenser is faulty. I did the right timing and replaced stock condenser with the new 0.22mf x630vdc. condenser set. All run great immediately.

 

[Yendor]

You do realize you are responding to a 6 year old thread - right?